October 2025 - Linux-stable-mirror

How to Speak to a Live Person Asiana Airlines: Tips and Tricks

by jacquelinegonza.lez3316.1＠gmail.com

Need to talk to a real person Asiana Airlines? Calling Asiana Airlines directly at 📞 1-866-284-3022. Whether you are trying to make a flight change, cancel your booking, ask about baggage, or resolve a booking issue, reaching a live agent can save you time, stress, and confusion. While automated systems are useful for simple tasks, some situations just need a human touch. In this guide, we will walk you through exactly how to reach a live person, what to prepare before calling, and alternate methods if the phone lines are busy. ☎️ First Things First: Call 1-866-284-3022 The most direct and reliable way to speak with a real Asiana Airlines representative is by calling 📞 1-866-284-3022. This is Frontier’s official customer service number and should be your go-to for: ✈️ Flight changes or cancellations 🧾 Refund or credit questions 🛄 Baggage issues 🔁 Name corrections 🛑 Check-in or boarding problems 💺 Seat selection and upgrades Pro Tip: When calling, try to do so during non-peak hours — early mornings or late evenings — to reduce your hold time. 🎧 How to Navigate the Automated Menu When you call 1-866-284-3022, you will first hear an automated system. To get through to a live person faster, follow these steps: Dial 1-866-284-3022 Wait for the automated greeting to begin Press “1” for English (or “2” for Spanish) Press “2” for existing reservations Press “0” to speak with an agent (you may need to press "0" more than once) 👉 If “0” does not work immediately, stay on the line. Sometimes the system transfers you to an agent after a brief wait without needing more input. If the lines are busy and you are placed on hold, do not hang up — wait times vary, but you will eventually reach someone. 🧾 What to Have Ready Before You Call To help the agent assist you faster, make sure you have the following details on hand: 📌 Your confirmation code or booking number 📌 The full name on the reservation 📌 Your flight date and destination 📌 Any relevant documents (ID, credit card, etc.) 📌 A notepad for writing down instructions or confirmation numbers If you are calling to fix a mistake or request a refund, be prepared to briefly explain the issue and possibly provide documentation via email upon request. ⏰ Best Times to Call 1-866-284-3022 Customer service lines can be busy, especially during: ⚠️ Holidays ⚠️ Severe weather or flight delays ⚠️ Early morning flight hours 🎯 For the best chance at a short wait, try calling during these times: 🕔 5:00 AM – 7:00 AM (EST) 🕘 9:00 PM – 11:00 PM (EST) 📅 Midweek (Tuesdays and Wednesdays) Avoid Mondays if possible — it is the busiest day for airlines. 🧑‍💻 Alternative Ways to Reach Asiana Airlines (If Phone Fails) If calling 📞 1-866-284-3022 does not work or you are stuck in a long queue, here are a few alternate ways to get help: 💬 1. Online Chat (Limited Availability) Visit www.flyfrontier.com Scroll down and look for the “Let’s Chat” option. This can connect you to a live agent or AI assistant, depending on availability. 📧 2. Email Support You can also submit a help request through their Customer Support Form online. Use this for non-urgent matters like refund requests or documentation review. 📱 3. Social Media Tweet or DM Asiana Airlines on platforms like Twitter/X (@FlyFrontier) or send a message via Facebook. Sometimes social media agents respond faster than the phone team during high-volume periods. 📲 4. Mobile App Download the Asiana Airlines App, log in, and navigate to “My Trips” or “Support” for quick options. While this will not guarantee a live agent, you might find answers to basic questions faster. ❗ Common Issues That Require a Live Agent While many tasks can be done online, certain problems are best resolved with a real person at 1-866-284-3022: 🛑 Double charges or billing issues 🔄 Complex flight changes involving multiple passengers 🛄 Lost or delayed baggage ✍️ Legal name changes (marriage, divorce, etc.) 🧑‍⚕️ Medical or accessibility needs during travel In these cases, avoid wasting time — call directly and ask for a live agent. 🚨 Beware of Fake Numbers and Scams Only use the official number: 📞 1-866-284-3022. Scammers often post fake “Frontier support” numbers online, asking for credit card info or login credentials. 🛡️ Never share your full credit card number or personal information with an unverified source. ✅ Final Thoughts Talking to a live person at an airline should not be this hard — but when it comes to Asiana Airlines, knowing the right steps and phone number makes all the difference. 🧠 Remember: Dial 📞 1-866-284-3022 Press 0 to reach a live agent Call during off-peak hours Have your booking info ready Use alternative methods if the line is too busy 💡 The sooner you reach out, the more options you'll have to resolve your issue. ✈️ Whether you are rebooking, fixing an error, or checking a flight, calling 1-866-284-3022 connects you with someone who can truly help.

3 weeks, 6 days

1
0
0 0

Need Customer Service? Here’s How to Talk to a Live Agent Air Mauritius

by jacquelinegonza.lez3316.1＠gmail.com

Need to talk to a real person Air Mauritius? Calling Air Mauritius directly at 📞 1-866-284-3022. Whether you are trying to make a flight change, cancel your booking, ask about baggage, or resolve a booking issue, reaching a live agent can save you time, stress, and confusion. While automated systems are useful for simple tasks, some situations just need a human touch. In this guide, we will walk you through exactly how to reach a live person, what to prepare before calling, and alternate methods if the phone lines are busy. ☎️ First Things First: Call 1-866-284-3022 The most direct and reliable way to speak with a real Air Mauritius representative is by calling 📞 1-866-284-3022. This is Frontier’s official customer service number and should be your go-to for: ✈️ Flight changes or cancellations 🧾 Refund or credit questions 🛄 Baggage issues 🔁 Name corrections 🛑 Check-in or boarding problems 💺 Seat selection and upgrades Pro Tip: When calling, try to do so during non-peak hours — early mornings or late evenings — to reduce your hold time. 🎧 How to Navigate the Automated Menu When you call 1-866-284-3022, you will first hear an automated system. To get through to a live person faster, follow these steps: Dial 1-866-284-3022 Wait for the automated greeting to begin Press “1” for English (or “2” for Spanish) Press “2” for existing reservations Press “0” to speak with an agent (you may need to press "0" more than once) 👉 If “0” does not work immediately, stay on the line. Sometimes the system transfers you to an agent after a brief wait without needing more input. If the lines are busy and you are placed on hold, do not hang up — wait times vary, but you will eventually reach someone. 🧾 What to Have Ready Before You Call To help the agent assist you faster, make sure you have the following details on hand: 📌 Your confirmation code or booking number 📌 The full name on the reservation 📌 Your flight date and destination 📌 Any relevant documents (ID, credit card, etc.) 📌 A notepad for writing down instructions or confirmation numbers If you are calling to fix a mistake or request a refund, be prepared to briefly explain the issue and possibly provide documentation via email upon request. ⏰ Best Times to Call 1-866-284-3022 Customer service lines can be busy, especially during: ⚠️ Holidays ⚠️ Severe weather or flight delays ⚠️ Early morning flight hours 🎯 For the best chance at a short wait, try calling during these times: 🕔 5:00 AM – 7:00 AM (EST) 🕘 9:00 PM – 11:00 PM (EST) 📅 Midweek (Tuesdays and Wednesdays) Avoid Mondays if possible — it is the busiest day for airlines. 🧑‍💻 Alternative Ways to Reach Air Mauritius (If Phone Fails) If calling 📞 1-866-284-3022 does not work or you are stuck in a long queue, here are a few alternate ways to get help: 💬 1. Online Chat (Limited Availability) Visit www.flyfrontier.com Scroll down and look for the “Let’s Chat” option. This can connect you to a live agent or AI assistant, depending on availability. 📧 2. Email Support You can also submit a help request through their Customer Support Form online. Use this for non-urgent matters like refund requests or documentation review. 📱 3. Social Media Tweet or DM Air Mauritius on platforms like Twitter/X (@FlyFrontier) or send a message via Facebook. Sometimes social media agents respond faster than the phone team during high-volume periods. 📲 4. Mobile App Download the Air Mauritius App, log in, and navigate to “My Trips” or “Support” for quick options. While this will not guarantee a live agent, you might find answers to basic questions faster. ❗ Common Issues That Require a Live Agent While many tasks can be done online, certain problems are best resolved with a real person at 1-866-284-3022: 🛑 Double charges or billing issues 🔄 Complex flight changes involving multiple passengers 🛄 Lost or delayed baggage ✍️ Legal name changes (marriage, divorce, etc.) 🧑‍⚕️ Medical or accessibility needs during travel In these cases, avoid wasting time — call directly and ask for a live agent. 🚨 Beware of Fake Numbers and Scams Only use the official number: 📞 1-866-284-3022. Scammers often post fake “Frontier support” numbers online, asking for credit card info or login credentials. 🛡️ Never share your full credit card number or personal information with an unverified source. ✅ Final Thoughts Talking to a live person at an airline should not be this hard — but when it comes to Air Mauritius, knowing the right steps and phone number makes all the difference. 🧠 Remember: Dial 📞 1-866-284-3022 Press 0 to reach a live agent Call during off-peak hours Have your booking info ready Use alternative methods if the line is too busy 💡 The sooner you reach out, the more options you'll have to resolve your issue. ✈️ Whether you are rebooking, fixing an error, or checking a flight, calling 1-866-284-3022 connects you with someone who can truly help.

3 weeks, 6 days

1
0
0 0

How to Contact a Live Agent Air Wisconsin for Assistance

by jacquelinegonza.lez3316.1＠gmail.com

Need to talk to a real person Air Wisconsin? Calling Air Wisconsin directly at 📞 1-866-284-3022. Whether you are trying to make a flight change, cancel your booking, ask about baggage, or resolve a booking issue, reaching a live agent can save you time, stress, and confusion. While automated systems are useful for simple tasks, some situations just need a human touch. In this guide, we will walk you through exactly how to reach a live person, what to prepare before calling, and alternate methods if the phone lines are busy. ☎️ First Things First: Call 1-866-284-3022 The most direct and reliable way to speak with a real Air Wisconsin representative is by calling 📞 1-866-284-3022. This is Frontier’s official customer service number and should be your go-to for: ✈️ Flight changes or cancellations 🧾 Refund or credit questions 🛄 Baggage issues 🔁 Name corrections 🛑 Check-in or boarding problems 💺 Seat selection and upgrades Pro Tip: When calling, try to do so during non-peak hours — early mornings or late evenings — to reduce your hold time. 🎧 How to Navigate the Automated Menu When you call 1-866-284-3022, you will first hear an automated system. To get through to a live person faster, follow these steps: Dial 1-866-284-3022 Wait for the automated greeting to begin Press “1” for English (or “2” for Spanish) Press “2” for existing reservations Press “0” to speak with an agent (you may need to press "0" more than once) 👉 If “0” does not work immediately, stay on the line. Sometimes the system transfers you to an agent after a brief wait without needing more input. If the lines are busy and you are placed on hold, do not hang up — wait times vary, but you will eventually reach someone. 🧾 What to Have Ready Before You Call To help the agent assist you faster, make sure you have the following details on hand: 📌 Your confirmation code or booking number 📌 The full name on the reservation 📌 Your flight date and destination 📌 Any relevant documents (ID, credit card, etc.) 📌 A notepad for writing down instructions or confirmation numbers If you are calling to fix a mistake or request a refund, be prepared to briefly explain the issue and possibly provide documentation via email upon request. ⏰ Best Times to Call 1-866-284-3022 Customer service lines can be busy, especially during: ⚠️ Holidays ⚠️ Severe weather or flight delays ⚠️ Early morning flight hours 🎯 For the best chance at a short wait, try calling during these times: 🕔 5:00 AM – 7:00 AM (EST) 🕘 9:00 PM – 11:00 PM (EST) 📅 Midweek (Tuesdays and Wednesdays) Avoid Mondays if possible — it is the busiest day for airlines. 🧑‍💻 Alternative Ways to Reach Air Wisconsin (If Phone Fails) If calling 📞 1-866-284-3022 does not work or you are stuck in a long queue, here are a few alternate ways to get help: 💬 1. Online Chat (Limited Availability) Visit www.flyfrontier.com Scroll down and look for the “Let’s Chat” option. This can connect you to a live agent or AI assistant, depending on availability. 📧 2. Email Support You can also submit a help request through their Customer Support Form online. Use this for non-urgent matters like refund requests or documentation review. 📱 3. Social Media Tweet or DM Air Wisconsin on platforms like Twitter/X (@FlyFrontier) or send a message via Facebook. Sometimes social media agents respond faster than the phone team during high-volume periods. 📲 4. Mobile App Download the Air Wisconsin App, log in, and navigate to “My Trips” or “Support” for quick options. While this will not guarantee a live agent, you might find answers to basic questions faster. ❗ Common Issues That Require a Live Agent While many tasks can be done online, certain problems are best resolved with a real person at 1-866-284-3022: 🛑 Double charges or billing issues 🔄 Complex flight changes involving multiple passengers 🛄 Lost or delayed baggage ✍️ Legal name changes (marriage, divorce, etc.) 🧑‍⚕️ Medical or accessibility needs during travel In these cases, avoid wasting time — call directly and ask for a live agent. 🚨 Beware of Fake Numbers and Scams Only use the official number: 📞 1-866-284-3022. Scammers often post fake “Frontier support” numbers online, asking for credit card info or login credentials. 🛡️ Never share your full credit card number or personal information with an unverified source. ✅ Final Thoughts Talking to a live person at an airline should not be this hard — but when it comes to Air Wisconsin, knowing the right steps and phone number makes all the difference. 🧠 Remember: Dial 📞 1-866-284-3022 Press 0 to reach a live agent Call during off-peak hours Have your booking info ready Use alternative methods if the line is too busy 💡 The sooner you reach out, the more options you'll have to resolve your issue. ✈️ Whether you are rebooking, fixing an error, or checking a flight, calling 1-866-284-3022 connects you with someone who can truly help.

3 weeks, 6 days

1
0
0 0

How to Easily Contact a Live Agent Air Seychelles for Help

by jacquelinegonza.lez3316.1＠gmail.com

Need to talk to a real person Air Seychelles? Calling Air Seychelles directly at 📞 1-866-284-3022. Whether you are trying to make a flight change, cancel your booking, ask about baggage, or resolve a booking issue, reaching a live agent can save you time, stress, and confusion. While automated systems are useful for simple tasks, some situations just need a human touch. In this guide, we will walk you through exactly how to reach a live person, what to prepare before calling, and alternate methods if the phone lines are busy. ☎️ First Things First: Call 1-866-284-3022 The most direct and reliable way to speak with a real Air Seychelles representative is by calling 📞 1-866-284-3022. This is Frontier’s official customer service number and should be your go-to for: ✈️ Flight changes or cancellations 🧾 Refund or credit questions 🛄 Baggage issues 🔁 Name corrections 🛑 Check-in or boarding problems 💺 Seat selection and upgrades Pro Tip: When calling, try to do so during non-peak hours — early mornings or late evenings — to reduce your hold time. 🎧 How to Navigate the Automated Menu When you call 1-866-284-3022, you will first hear an automated system. To get through to a live person faster, follow these steps: Dial 1-866-284-3022 Wait for the automated greeting to begin Press “1” for English (or “2” for Spanish) Press “2” for existing reservations Press “0” to speak with an agent (you may need to press "0" more than once) 👉 If “0” does not work immediately, stay on the line. Sometimes the system transfers you to an agent after a brief wait without needing more input. If the lines are busy and you are placed on hold, do not hang up — wait times vary, but you will eventually reach someone. 🧾 What to Have Ready Before You Call To help the agent assist you faster, make sure you have the following details on hand: 📌 Your confirmation code or booking number 📌 The full name on the reservation 📌 Your flight date and destination 📌 Any relevant documents (ID, credit card, etc.) 📌 A notepad for writing down instructions or confirmation numbers If you are calling to fix a mistake or request a refund, be prepared to briefly explain the issue and possibly provide documentation via email upon request. ⏰ Best Times to Call 1-866-284-3022 Customer service lines can be busy, especially during: ⚠️ Holidays ⚠️ Severe weather or flight delays ⚠️ Early morning flight hours 🎯 For the best chance at a short wait, try calling during these times: 🕔 5:00 AM – 7:00 AM (EST) 🕘 9:00 PM – 11:00 PM (EST) 📅 Midweek (Tuesdays and Wednesdays) Avoid Mondays if possible — it is the busiest day for airlines. 🧑‍💻 Alternative Ways to Reach Air Seychelles (If Phone Fails) If calling 📞 1-866-284-3022 does not work or you are stuck in a long queue, here are a few alternate ways to get help: 💬 1. Online Chat (Limited Availability) Visit www.flyfrontier.com Scroll down and look for the “Let’s Chat” option. This can connect you to a live agent or AI assistant, depending on availability. 📧 2. Email Support You can also submit a help request through their Customer Support Form online. Use this for non-urgent matters like refund requests or documentation review. 📱 3. Social Media Tweet or DM Air Seychelles on platforms like Twitter/X (@FlyFrontier) or send a message via Facebook. Sometimes social media agents respond faster than the phone team during high-volume periods. 📲 4. Mobile App Download the Air Seychelles App, log in, and navigate to “My Trips” or “Support” for quick options. While this will not guarantee a live agent, you might find answers to basic questions faster. ❗ Common Issues That Require a Live Agent While many tasks can be done online, certain problems are best resolved with a real person at 1-866-284-3022: 🛑 Double charges or billing issues 🔄 Complex flight changes involving multiple passengers 🛄 Lost or delayed baggage ✍️ Legal name changes (marriage, divorce, etc.) 🧑‍⚕️ Medical or accessibility needs during travel In these cases, avoid wasting time — call directly and ask for a live agent. 🚨 Beware of Fake Numbers and Scams Only use the official number: 📞 1-866-284-3022. Scammers often post fake “Frontier support” numbers online, asking for credit card info or login credentials. 🛡️ Never share your full credit card number or personal information with an unverified source. ✅ Final Thoughts Talking to a live person at an airline should not be this hard — but when it comes to Air Seychelles, knowing the right steps and phone number makes all the difference. 🧠 Remember: Dial 📞 1-866-284-3022 Press 0 to reach a live agent Call during off-peak hours Have your booking info ready Use alternative methods if the line is too busy 💡 The sooner you reach out, the more options you'll have to resolve your issue. ✈️ Whether you are rebooking, fixing an error, or checking a flight, calling 1-866-284-3022 connects you with someone who can truly help.

3 weeks, 6 days

1
0
0 0

[PATCH] virtio: vdpa: Fix reference count leak in octep_sriov_enable()

by Miaoqian Lin

pci_get_device() will increase the reference count for the returned pci_dev, and also decrease the reference count for the input parameter from if it is not NULL. If we break the loop in with 'vf_pdev' not NULL. We need to call pci_dev_put() to decrease the reference count. Found via static anlaysis and this is similar to commit c508eb042d97 ("perf/x86/intel/uncore: Fix reference count leak in sad_cfg_iio_topology()") Fixes: 8b6c724cdab8 ("virtio: vdpa: vDPA driver for Marvell OCTEON DPU devices") Cc: stable(a)vger.kernel.org Signed-off-by: Miaoqian Lin <linmq006(a)gmail.com> --- drivers/vdpa/octeon_ep/octep_vdpa_main.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/vdpa/octeon_ep/octep_vdpa_main.c b/drivers/vdpa/octeon_ep/octep_vdpa_main.c index 9e8d07078606..31a02e7fd7f2 100644 --- a/drivers/vdpa/octeon_ep/octep_vdpa_main.c +++ b/drivers/vdpa/octeon_ep/octep_vdpa_main.c @@ -736,6 +736,7 @@ static int octep_sriov_enable(struct pci_dev *pdev, int num_vfs) octep_vdpa_assign_barspace(vf_pdev, pdev, index); if (++index == num_vfs) { done = true; + pci_dev_put(vf_pdev); break; } } -- 2.39.5 (Apple Git-154)

3 weeks, 6 days

1
0
0 0

[PATCH] usb: cdns3: Fix double resource release in cdns3_pci_probe

by Miaoqian Lin

The driver uses pcim_enable_device() to enable the PCI device, the device will be automatically disabled on driver detach through the managed device framework. The manual pci_disable_device() calls in the error paths are therefore redundant and should be removed. Found via static anlaysis and this is similar to commit 99ca0b57e49f ("thermal: intel: int340x: processor: Fix warning during module unload"). Fixes: 7733f6c32e36 ("usb: cdns3: Add Cadence USB3 DRD Driver") Cc: stable(a)vger.kernel.org Signed-off-by: Miaoqian Lin <linmq006(a)gmail.com> --- drivers/usb/cdns3/cdns3-pci-wrap.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-) diff --git a/drivers/usb/cdns3/cdns3-pci-wrap.c b/drivers/usb/cdns3/cdns3-pci-wrap.c index 3b3b3dc75f35..57f57c24c663 100644 --- a/drivers/usb/cdns3/cdns3-pci-wrap.c +++ b/drivers/usb/cdns3/cdns3-pci-wrap.c @@ -98,10 +98,8 @@ static int cdns3_pci_probe(struct pci_dev *pdev, wrap = pci_get_drvdata(func); } else { wrap = kzalloc(sizeof(*wrap), GFP_KERNEL); - if (!wrap) { - pci_disable_device(pdev); + if (!wrap) return -ENOMEM; - } } res = wrap->dev_res; @@ -160,7 +158,6 @@ static int cdns3_pci_probe(struct pci_dev *pdev, /* register platform device */ wrap->plat_dev = platform_device_register_full(&plat_info); if (IS_ERR(wrap->plat_dev)) { - pci_disable_device(pdev); err = PTR_ERR(wrap->plat_dev); kfree(wrap); return err; -- 2.39.5 (Apple Git-154)

3 weeks, 6 days

2
1
0 0

[PATCH] perf: arm_cspmu: fix device leak in arm_cspmu_impl_unregister

by Ma Ke

arm_cspmu_impl_unregister() utilizes driver_find_device() to locate matching devices. driver_find_device() increments the ref count of the found device by calling get_device(), but arm_cspmu_impl_unregister() fails to call put_device() to decrement the reference count after processing each device. This results in a reference count leak of the device objects, which prevents devices from being properly released and causes a memory leak. Fix the leak by adding put_device() after device_release_driver() in the while loop. Found by code review. Cc: stable(a)vger.kernel.org Fixes: bfc653aa89cb ("perf: arm_cspmu: Separate Arm and vendor module") Signed-off-by: Ma Ke <make24(a)iscas.ac.cn> --- drivers/perf/arm_cspmu/arm_cspmu.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/drivers/perf/arm_cspmu/arm_cspmu.c b/drivers/perf/arm_cspmu/arm_cspmu.c index efa9b229e701..e0d4293f06f9 100644 --- a/drivers/perf/arm_cspmu/arm_cspmu.c +++ b/drivers/perf/arm_cspmu/arm_cspmu.c @@ -1365,8 +1365,10 @@ void arm_cspmu_impl_unregister(const struct arm_cspmu_impl_match *impl_match) /* Unbind the driver from all matching backend devices. */ while ((dev = driver_find_device(&arm_cspmu_driver.driver, NULL, - match, arm_cspmu_match_device))) + match, arm_cspmu_match_device))) { device_release_driver(dev); + put_device(dev); + } mutex_lock(&arm_cspmu_lock); -- 2.17.1

3 weeks, 6 days

1
0
0 0

[PATCH] ARM: tegra: fix device leak on tegra ahb lookup

by Ma Ke

tegra_ahb_enable_smmu() utilizes driver_find_device_by_of_node() which internally calls driver_find_device() to locate the matching device. driver_find_device() increments the ref count of the found device by calling get_device(), but tegra_ahb_enable_smmu() fails to call put_device() to decrement the reference count before returning. This results in a reference count leak of the device, which may prevent the device from being properly released and cause a memory leak. Found by code review. Cc: stable(a)vger.kernel.org Fixes: 89c788bab1f0 ("ARM: tegra: Add SMMU enabler in AHB") Signed-off-by: Ma Ke <make24(a)iscas.ac.cn> --- drivers/amba/tegra-ahb.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/amba/tegra-ahb.c b/drivers/amba/tegra-ahb.c index c0e8b765522d..6c306d017b67 100644 --- a/drivers/amba/tegra-ahb.c +++ b/drivers/amba/tegra-ahb.c @@ -147,6 +147,7 @@ int tegra_ahb_enable_smmu(struct device_node *dn) val = gizmo_readl(ahb, AHB_ARBITRATION_XBAR_CTRL); val |= AHB_ARBITRATION_XBAR_CTRL_SMMU_INIT_DONE; gizmo_writel(ahb, val, AHB_ARBITRATION_XBAR_CTRL); + put_device(dev); return 0; } EXPORT_SYMBOL(tegra_ahb_enable_smmu); -- 2.17.1

3 weeks, 6 days

1
0
0 0

FAILED: patch "[PATCH] devcoredump: Fix circular locking dependency with" failed to apply to 5.15-stable tree

by gregkh＠linuxfoundation.org

The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <stable(a)vger.kernel.org>. To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y git checkout FETCH_HEAD git cherry-pick -x a91c8096590bd7801a26454789f2992094fe36da # <resolve conflicts, build, test, etc.> git commit -s git send-email --to '<stable(a)vger.kernel.org>' --in-reply-to '2025102623-science-evergreen-c201@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^.. Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ From a91c8096590bd7801a26454789f2992094fe36da Mon Sep 17 00:00:00 2001 From: Maarten Lankhorst <dev(a)lankhorst.se> Date: Wed, 23 Jul 2025 16:24:16 +0200 Subject: [PATCH] devcoredump: Fix circular locking dependency with devcd->mutex. The original code causes a circular locking dependency found by lockdep. ====================================================== WARNING: possible circular locking dependency detected 6.16.0-rc6-lgci-xe-xe-pw-151626v3+ #1 Tainted: G S U ------------------------------------------------------ xe_fault_inject/5091 is trying to acquire lock: ffff888156815688 ((work_completion)(&(&devcd->del_wk)->work)){+.+.}-{0:0}, at: __flush_work+0x25d/0x660 but task is already holding lock: ffff888156815620 (&devcd->mutex){+.+.}-{3:3}, at: dev_coredump_put+0x3f/0xa0 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (&devcd->mutex){+.+.}-{3:3}: mutex_lock_nested+0x4e/0xc0 devcd_data_write+0x27/0x90 sysfs_kf_bin_write+0x80/0xf0 kernfs_fop_write_iter+0x169/0x220 vfs_write+0x293/0x560 ksys_write+0x72/0xf0 __x64_sys_write+0x19/0x30 x64_sys_call+0x2bf/0x2660 do_syscall_64+0x93/0xb60 entry_SYSCALL_64_after_hwframe+0x76/0x7e -> #1 (kn->active#236){++++}-{0:0}: kernfs_drain+0x1e2/0x200 __kernfs_remove+0xae/0x400 kernfs_remove_by_name_ns+0x5d/0xc0 remove_files+0x54/0x70 sysfs_remove_group+0x3d/0xa0 sysfs_remove_groups+0x2e/0x60 device_remove_attrs+0xc7/0x100 device_del+0x15d/0x3b0 devcd_del+0x19/0x30 process_one_work+0x22b/0x6f0 worker_thread+0x1e8/0x3d0 kthread+0x11c/0x250 ret_from_fork+0x26c/0x2e0 ret_from_fork_asm+0x1a/0x30 -> #0 ((work_completion)(&(&devcd->del_wk)->work)){+.+.}-{0:0}: __lock_acquire+0x1661/0x2860 lock_acquire+0xc4/0x2f0 __flush_work+0x27a/0x660 flush_delayed_work+0x5d/0xa0 dev_coredump_put+0x63/0xa0 xe_driver_devcoredump_fini+0x12/0x20 [xe] devm_action_release+0x12/0x30 release_nodes+0x3a/0x120 devres_release_all+0x8a/0xd0 device_unbind_cleanup+0x12/0x80 device_release_driver_internal+0x23a/0x280 device_driver_detach+0x14/0x20 unbind_store+0xaf/0xc0 drv_attr_store+0x21/0x50 sysfs_kf_write+0x4a/0x80 kernfs_fop_write_iter+0x169/0x220 vfs_write+0x293/0x560 ksys_write+0x72/0xf0 __x64_sys_write+0x19/0x30 x64_sys_call+0x2bf/0x2660 do_syscall_64+0x93/0xb60 entry_SYSCALL_64_after_hwframe+0x76/0x7e other info that might help us debug this: Chain exists of: (work_completion)(&(&devcd->del_wk)->work) --> kn->active#236 --> &devcd->mutex Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&devcd->mutex); lock(kn->active#236); lock(&devcd->mutex); lock((work_completion)(&(&devcd->del_wk)->work)); *** DEADLOCK *** 5 locks held by xe_fault_inject/5091: #0: ffff8881129f9488 (sb_writers#5){.+.+}-{0:0}, at: ksys_write+0x72/0xf0 #1: ffff88810c755078 (&of->mutex#2){+.+.}-{3:3}, at: kernfs_fop_write_iter+0x123/0x220 #2: ffff8881054811a0 (&dev->mutex){....}-{3:3}, at: device_release_driver_internal+0x55/0x280 #3: ffff888156815620 (&devcd->mutex){+.+.}-{3:3}, at: dev_coredump_put+0x3f/0xa0 #4: ffffffff8359e020 (rcu_read_lock){....}-{1:2}, at: __flush_work+0x72/0x660 stack backtrace: CPU: 14 UID: 0 PID: 5091 Comm: xe_fault_inject Tainted: G S U 6.16.0-rc6-lgci-xe-xe-pw-151626v3+ #1 PREEMPT_{RT,(lazy)} Tainted: [S]=CPU_OUT_OF_SPEC, [U]=USER Hardware name: Micro-Star International Co., Ltd. MS-7D25/PRO Z690-A DDR4(MS-7D25), BIOS 1.10 12/13/2021 Call Trace: <TASK> dump_stack_lvl+0x91/0xf0 dump_stack+0x10/0x20 print_circular_bug+0x285/0x360 check_noncircular+0x135/0x150 ? register_lock_class+0x48/0x4a0 __lock_acquire+0x1661/0x2860 lock_acquire+0xc4/0x2f0 ? __flush_work+0x25d/0x660 ? mark_held_locks+0x46/0x90 ? __flush_work+0x25d/0x660 __flush_work+0x27a/0x660 ? __flush_work+0x25d/0x660 ? trace_hardirqs_on+0x1e/0xd0 ? __pfx_wq_barrier_func+0x10/0x10 flush_delayed_work+0x5d/0xa0 dev_coredump_put+0x63/0xa0 xe_driver_devcoredump_fini+0x12/0x20 [xe] devm_action_release+0x12/0x30 release_nodes+0x3a/0x120 devres_release_all+0x8a/0xd0 device_unbind_cleanup+0x12/0x80 device_release_driver_internal+0x23a/0x280 ? bus_find_device+0xa8/0xe0 device_driver_detach+0x14/0x20 unbind_store+0xaf/0xc0 drv_attr_store+0x21/0x50 sysfs_kf_write+0x4a/0x80 kernfs_fop_write_iter+0x169/0x220 vfs_write+0x293/0x560 ksys_write+0x72/0xf0 __x64_sys_write+0x19/0x30 x64_sys_call+0x2bf/0x2660 do_syscall_64+0x93/0xb60 ? __f_unlock_pos+0x15/0x20 ? __x64_sys_getdents64+0x9b/0x130 ? __pfx_filldir64+0x10/0x10 ? do_syscall_64+0x1a2/0xb60 ? clear_bhb_loop+0x30/0x80 ? clear_bhb_loop+0x30/0x80 entry_SYSCALL_64_after_hwframe+0x76/0x7e RIP: 0033:0x76e292edd574 Code: c7 00 16 00 00 00 b8 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 f3 0f 1e fa 80 3d d5 ea 0e 00 00 74 13 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 54 c3 0f 1f 00 55 48 89 e5 48 83 ec 20 48 89 RSP: 002b:00007fffe247a828 EFLAGS: 00000202 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 000076e292edd574 RDX: 000000000000000c RSI: 00006267f6306063 RDI: 000000000000000b RBP: 000000000000000c R08: 000076e292fc4b20 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000202 R12: 00006267f6306063 R13: 000000000000000b R14: 00006267e6859c00 R15: 000076e29322a000 </TASK> xe 0000:03:00.0: [drm] Xe device coredump has been deleted. Fixes: 01daccf74832 ("devcoredump : Serialize devcd_del work") Cc: Mukesh Ojha <quic_mojha(a)quicinc.com> Cc: Greg Kroah-Hartman <gregkh(a)linuxfoundation.org> Cc: Johannes Berg <johannes(a)sipsolutions.net> Cc: Rafael J. Wysocki <rafael(a)kernel.org> Cc: Danilo Krummrich <dakr(a)kernel.org> Cc: linux-kernel(a)vger.kernel.org Cc: stable(a)vger.kernel.org # v6.1+ Signed-off-by: Maarten Lankhorst <dev(a)lankhorst.se> Cc: Matthew Brost <matthew.brost(a)intel.com> Acked-by: Mukesh Ojha <mukesh.ojha(a)oss.qualcomm.com> Link: https://lore.kernel.org/r/20250723142416.1020423-1-dev@lankhorst.se Signed-off-by: Greg Kroah-Hartman <gregkh(a)linuxfoundation.org> diff --git a/drivers/base/devcoredump.c b/drivers/base/devcoredump.c index 37faf6156d7c..55bdc7f5e59d 100644 --- a/drivers/base/devcoredump.c +++ b/drivers/base/devcoredump.c @@ -23,50 +23,46 @@ struct devcd_entry { void *data; size_t datalen; /* - * Here, mutex is required to serialize the calls to del_wk work between - * user/kernel space which happens when devcd is added with device_add() - * and that sends uevent to user space. User space reads the uevents, - * and calls to devcd_data_write() which try to modify the work which is - * not even initialized/queued from devcoredump. + * There are 2 races for which mutex is required. * + * The first race is between device creation and userspace writing to + * schedule immediately destruction. * + * This race is handled by arming the timer before device creation, but + * when device creation fails the timer still exists. * - * cpu0(X) cpu1(Y) + * To solve this, hold the mutex during device_add(), and set + * init_completed on success before releasing the mutex. * - * dev_coredump() uevent sent to user space - * device_add() ======================> user space process Y reads the - * uevents writes to devcd fd - * which results into writes to + * That way the timer will never fire until device_add() is called, + * it will do nothing if init_completed is not set. The timer is also + * cancelled in that case. * - * devcd_data_write() - * mod_delayed_work() - * try_to_grab_pending() - * timer_delete() - * debug_assert_init() - * INIT_DELAYED_WORK() - * schedule_delayed_work() - * - * - * Also, mutex alone would not be enough to avoid scheduling of - * del_wk work after it get flush from a call to devcd_free() - * mentioned as below. - * - * disabled_store() - * devcd_free() - * mutex_lock() devcd_data_write() - * flush_delayed_work() - * mutex_unlock() - * mutex_lock() - * mod_delayed_work() - * mutex_unlock() - * So, delete_work flag is required. + * The second race involves multiple parallel invocations of devcd_free(), + * add a deleted flag so only 1 can call the destructor. */ struct mutex mutex; - bool delete_work; + bool init_completed, deleted; struct module *owner; ssize_t (*read)(char *buffer, loff_t offset, size_t count, void *data, size_t datalen); void (*free)(void *data); + /* + * If nothing interferes and device_add() was returns success, + * del_wk will destroy the device after the timer fires. + * + * Multiple userspace processes can interfere in the working of the timer: + * - Writing to the coredump will reschedule the timer to run immediately, + * if still armed. + * + * This is handled by using "if (cancel_delayed_work()) { + * schedule_delayed_work() }", to prevent re-arming after having + * been previously fired. + * - Writing to /sys/class/devcoredump/disabled will destroy the + * coredump synchronously. + * This is handled by using disable_delayed_work_sync(), and then + * checking if deleted flag is set with &devcd->mutex held. + */ struct delayed_work del_wk; struct device *failing_dev; }; @@ -95,14 +91,27 @@ static void devcd_dev_release(struct device *dev) kfree(devcd); } +static void __devcd_del(struct devcd_entry *devcd) +{ + devcd->deleted = true; + device_del(&devcd->devcd_dev); + put_device(&devcd->devcd_dev); +} + static void devcd_del(struct work_struct *wk) { struct devcd_entry *devcd; + bool init_completed; devcd = container_of(wk, struct devcd_entry, del_wk.work); - device_del(&devcd->devcd_dev); - put_device(&devcd->devcd_dev); + /* devcd->mutex serializes against dev_coredumpm_timeout */ + mutex_lock(&devcd->mutex); + init_completed = devcd->init_completed; + mutex_unlock(&devcd->mutex); + + if (init_completed) + __devcd_del(devcd); } static ssize_t devcd_data_read(struct file *filp, struct kobject *kobj, @@ -122,12 +131,12 @@ static ssize_t devcd_data_write(struct file *filp, struct kobject *kobj, struct device *dev = kobj_to_dev(kobj); struct devcd_entry *devcd = dev_to_devcd(dev); - mutex_lock(&devcd->mutex); - if (!devcd->delete_work) { - devcd->delete_work = true; - mod_delayed_work(system_wq, &devcd->del_wk, 0); - } - mutex_unlock(&devcd->mutex); + /* + * Although it's tempting to use mod_delayed work here, + * that will cause a reschedule if the timer already fired. + */ + if (cancel_delayed_work(&devcd->del_wk)) + schedule_delayed_work(&devcd->del_wk, 0); return count; } @@ -151,11 +160,21 @@ static int devcd_free(struct device *dev, void *data) { struct devcd_entry *devcd = dev_to_devcd(dev); + /* + * To prevent a race with devcd_data_write(), disable work and + * complete manually instead. + * + * We cannot rely on the return value of + * disable_delayed_work_sync() here, because it might be in the + * middle of a cancel_delayed_work + schedule_delayed_work pair. + * + * devcd->mutex here guards against multiple parallel invocations + * of devcd_free(). + */ + disable_delayed_work_sync(&devcd->del_wk); mutex_lock(&devcd->mutex); - if (!devcd->delete_work) - devcd->delete_work = true; - - flush_delayed_work(&devcd->del_wk); + if (!devcd->deleted) + __devcd_del(devcd); mutex_unlock(&devcd->mutex); return 0; } @@ -179,12 +198,10 @@ static ssize_t disabled_show(const struct class *class, const struct class_attri * put_device() <- last reference * error = fn(dev, data) devcd_dev_release() * devcd_free(dev, data) kfree(devcd) - * mutex_lock(&devcd->mutex); * * * In the above diagram, it looks like disabled_store() would be racing with parallelly - * running devcd_del() and result in memory abort while acquiring devcd->mutex which - * is called after kfree of devcd memory after dropping its last reference with + * running devcd_del() and result in memory abort after dropping its last reference with * put_device(). However, this will not happens as fn(dev, data) runs * with its own reference to device via klist_node so it is not its last reference. * so, above situation would not occur. @@ -374,7 +391,7 @@ void dev_coredumpm_timeout(struct device *dev, struct module *owner, devcd->read = read; devcd->free = free; devcd->failing_dev = get_device(dev); - devcd->delete_work = false; + devcd->deleted = false; mutex_init(&devcd->mutex); device_initialize(&devcd->devcd_dev); @@ -383,8 +400,14 @@ void dev_coredumpm_timeout(struct device *dev, struct module *owner, atomic_inc_return(&devcd_count)); devcd->devcd_dev.class = &devcd_class; - mutex_lock(&devcd->mutex); dev_set_uevent_suppress(&devcd->devcd_dev, true); + + /* devcd->mutex prevents devcd_del() completing until init finishes */ + mutex_lock(&devcd->mutex); + devcd->init_completed = false; + INIT_DELAYED_WORK(&devcd->del_wk, devcd_del); + schedule_delayed_work(&devcd->del_wk, timeout); + if (device_add(&devcd->devcd_dev)) goto put_device; @@ -401,13 +424,20 @@ void dev_coredumpm_timeout(struct device *dev, struct module *owner, dev_set_uevent_suppress(&devcd->devcd_dev, false); kobject_uevent(&devcd->devcd_dev.kobj, KOBJ_ADD); - INIT_DELAYED_WORK(&devcd->del_wk, devcd_del); - schedule_delayed_work(&devcd->del_wk, timeout); + + /* + * Safe to run devcd_del() now that we are done with devcd_dev. + * Alternatively we could have taken a ref on devcd_dev before + * dropping the lock. + */ + devcd->init_completed = true; mutex_unlock(&devcd->mutex); return; put_device: - put_device(&devcd->devcd_dev); mutex_unlock(&devcd->mutex); + cancel_delayed_work_sync(&devcd->del_wk); + put_device(&devcd->devcd_dev); + put_module: module_put(owner); free:

3 weeks, 6 days

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FAILED: patch "[PATCH] devcoredump: Fix circular locking dependency with" failed to apply to 6.1-stable tree

by gregkh＠linuxfoundation.org

The patch below does not apply to the 6.1-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <stable(a)vger.kernel.org>. To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y git checkout FETCH_HEAD git cherry-pick -x a91c8096590bd7801a26454789f2992094fe36da # <resolve conflicts, build, test, etc.> git commit -s git send-email --to '<stable(a)vger.kernel.org>' --in-reply-to '2025102622-alibi-unloved-94ad@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^.. Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ From a91c8096590bd7801a26454789f2992094fe36da Mon Sep 17 00:00:00 2001 From: Maarten Lankhorst <dev(a)lankhorst.se> Date: Wed, 23 Jul 2025 16:24:16 +0200 Subject: [PATCH] devcoredump: Fix circular locking dependency with devcd->mutex. The original code causes a circular locking dependency found by lockdep. ====================================================== WARNING: possible circular locking dependency detected 6.16.0-rc6-lgci-xe-xe-pw-151626v3+ #1 Tainted: G S U ------------------------------------------------------ xe_fault_inject/5091 is trying to acquire lock: ffff888156815688 ((work_completion)(&(&devcd->del_wk)->work)){+.+.}-{0:0}, at: __flush_work+0x25d/0x660 but task is already holding lock: ffff888156815620 (&devcd->mutex){+.+.}-{3:3}, at: dev_coredump_put+0x3f/0xa0 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (&devcd->mutex){+.+.}-{3:3}: mutex_lock_nested+0x4e/0xc0 devcd_data_write+0x27/0x90 sysfs_kf_bin_write+0x80/0xf0 kernfs_fop_write_iter+0x169/0x220 vfs_write+0x293/0x560 ksys_write+0x72/0xf0 __x64_sys_write+0x19/0x30 x64_sys_call+0x2bf/0x2660 do_syscall_64+0x93/0xb60 entry_SYSCALL_64_after_hwframe+0x76/0x7e -> #1 (kn->active#236){++++}-{0:0}: kernfs_drain+0x1e2/0x200 __kernfs_remove+0xae/0x400 kernfs_remove_by_name_ns+0x5d/0xc0 remove_files+0x54/0x70 sysfs_remove_group+0x3d/0xa0 sysfs_remove_groups+0x2e/0x60 device_remove_attrs+0xc7/0x100 device_del+0x15d/0x3b0 devcd_del+0x19/0x30 process_one_work+0x22b/0x6f0 worker_thread+0x1e8/0x3d0 kthread+0x11c/0x250 ret_from_fork+0x26c/0x2e0 ret_from_fork_asm+0x1a/0x30 -> #0 ((work_completion)(&(&devcd->del_wk)->work)){+.+.}-{0:0}: __lock_acquire+0x1661/0x2860 lock_acquire+0xc4/0x2f0 __flush_work+0x27a/0x660 flush_delayed_work+0x5d/0xa0 dev_coredump_put+0x63/0xa0 xe_driver_devcoredump_fini+0x12/0x20 [xe] devm_action_release+0x12/0x30 release_nodes+0x3a/0x120 devres_release_all+0x8a/0xd0 device_unbind_cleanup+0x12/0x80 device_release_driver_internal+0x23a/0x280 device_driver_detach+0x14/0x20 unbind_store+0xaf/0xc0 drv_attr_store+0x21/0x50 sysfs_kf_write+0x4a/0x80 kernfs_fop_write_iter+0x169/0x220 vfs_write+0x293/0x560 ksys_write+0x72/0xf0 __x64_sys_write+0x19/0x30 x64_sys_call+0x2bf/0x2660 do_syscall_64+0x93/0xb60 entry_SYSCALL_64_after_hwframe+0x76/0x7e other info that might help us debug this: Chain exists of: (work_completion)(&(&devcd->del_wk)->work) --> kn->active#236 --> &devcd->mutex Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&devcd->mutex); lock(kn->active#236); lock(&devcd->mutex); lock((work_completion)(&(&devcd->del_wk)->work)); *** DEADLOCK *** 5 locks held by xe_fault_inject/5091: #0: ffff8881129f9488 (sb_writers#5){.+.+}-{0:0}, at: ksys_write+0x72/0xf0 #1: ffff88810c755078 (&of->mutex#2){+.+.}-{3:3}, at: kernfs_fop_write_iter+0x123/0x220 #2: ffff8881054811a0 (&dev->mutex){....}-{3:3}, at: device_release_driver_internal+0x55/0x280 #3: ffff888156815620 (&devcd->mutex){+.+.}-{3:3}, at: dev_coredump_put+0x3f/0xa0 #4: ffffffff8359e020 (rcu_read_lock){....}-{1:2}, at: __flush_work+0x72/0x660 stack backtrace: CPU: 14 UID: 0 PID: 5091 Comm: xe_fault_inject Tainted: G S U 6.16.0-rc6-lgci-xe-xe-pw-151626v3+ #1 PREEMPT_{RT,(lazy)} Tainted: [S]=CPU_OUT_OF_SPEC, [U]=USER Hardware name: Micro-Star International Co., Ltd. MS-7D25/PRO Z690-A DDR4(MS-7D25), BIOS 1.10 12/13/2021 Call Trace: <TASK> dump_stack_lvl+0x91/0xf0 dump_stack+0x10/0x20 print_circular_bug+0x285/0x360 check_noncircular+0x135/0x150 ? register_lock_class+0x48/0x4a0 __lock_acquire+0x1661/0x2860 lock_acquire+0xc4/0x2f0 ? __flush_work+0x25d/0x660 ? mark_held_locks+0x46/0x90 ? __flush_work+0x25d/0x660 __flush_work+0x27a/0x660 ? __flush_work+0x25d/0x660 ? trace_hardirqs_on+0x1e/0xd0 ? __pfx_wq_barrier_func+0x10/0x10 flush_delayed_work+0x5d/0xa0 dev_coredump_put+0x63/0xa0 xe_driver_devcoredump_fini+0x12/0x20 [xe] devm_action_release+0x12/0x30 release_nodes+0x3a/0x120 devres_release_all+0x8a/0xd0 device_unbind_cleanup+0x12/0x80 device_release_driver_internal+0x23a/0x280 ? bus_find_device+0xa8/0xe0 device_driver_detach+0x14/0x20 unbind_store+0xaf/0xc0 drv_attr_store+0x21/0x50 sysfs_kf_write+0x4a/0x80 kernfs_fop_write_iter+0x169/0x220 vfs_write+0x293/0x560 ksys_write+0x72/0xf0 __x64_sys_write+0x19/0x30 x64_sys_call+0x2bf/0x2660 do_syscall_64+0x93/0xb60 ? __f_unlock_pos+0x15/0x20 ? __x64_sys_getdents64+0x9b/0x130 ? __pfx_filldir64+0x10/0x10 ? do_syscall_64+0x1a2/0xb60 ? clear_bhb_loop+0x30/0x80 ? clear_bhb_loop+0x30/0x80 entry_SYSCALL_64_after_hwframe+0x76/0x7e RIP: 0033:0x76e292edd574 Code: c7 00 16 00 00 00 b8 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 f3 0f 1e fa 80 3d d5 ea 0e 00 00 74 13 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 54 c3 0f 1f 00 55 48 89 e5 48 83 ec 20 48 89 RSP: 002b:00007fffe247a828 EFLAGS: 00000202 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 000076e292edd574 RDX: 000000000000000c RSI: 00006267f6306063 RDI: 000000000000000b RBP: 000000000000000c R08: 000076e292fc4b20 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000202 R12: 00006267f6306063 R13: 000000000000000b R14: 00006267e6859c00 R15: 000076e29322a000 </TASK> xe 0000:03:00.0: [drm] Xe device coredump has been deleted. Fixes: 01daccf74832 ("devcoredump : Serialize devcd_del work") Cc: Mukesh Ojha <quic_mojha(a)quicinc.com> Cc: Greg Kroah-Hartman <gregkh(a)linuxfoundation.org> Cc: Johannes Berg <johannes(a)sipsolutions.net> Cc: Rafael J. Wysocki <rafael(a)kernel.org> Cc: Danilo Krummrich <dakr(a)kernel.org> Cc: linux-kernel(a)vger.kernel.org Cc: stable(a)vger.kernel.org # v6.1+ Signed-off-by: Maarten Lankhorst <dev(a)lankhorst.se> Cc: Matthew Brost <matthew.brost(a)intel.com> Acked-by: Mukesh Ojha <mukesh.ojha(a)oss.qualcomm.com> Link: https://lore.kernel.org/r/20250723142416.1020423-1-dev@lankhorst.se Signed-off-by: Greg Kroah-Hartman <gregkh(a)linuxfoundation.org> diff --git a/drivers/base/devcoredump.c b/drivers/base/devcoredump.c index 37faf6156d7c..55bdc7f5e59d 100644 --- a/drivers/base/devcoredump.c +++ b/drivers/base/devcoredump.c @@ -23,50 +23,46 @@ struct devcd_entry { void *data; size_t datalen; /* - * Here, mutex is required to serialize the calls to del_wk work between - * user/kernel space which happens when devcd is added with device_add() - * and that sends uevent to user space. User space reads the uevents, - * and calls to devcd_data_write() which try to modify the work which is - * not even initialized/queued from devcoredump. + * There are 2 races for which mutex is required. * + * The first race is between device creation and userspace writing to + * schedule immediately destruction. * + * This race is handled by arming the timer before device creation, but + * when device creation fails the timer still exists. * - * cpu0(X) cpu1(Y) + * To solve this, hold the mutex during device_add(), and set + * init_completed on success before releasing the mutex. * - * dev_coredump() uevent sent to user space - * device_add() ======================> user space process Y reads the - * uevents writes to devcd fd - * which results into writes to + * That way the timer will never fire until device_add() is called, + * it will do nothing if init_completed is not set. The timer is also + * cancelled in that case. * - * devcd_data_write() - * mod_delayed_work() - * try_to_grab_pending() - * timer_delete() - * debug_assert_init() - * INIT_DELAYED_WORK() - * schedule_delayed_work() - * - * - * Also, mutex alone would not be enough to avoid scheduling of - * del_wk work after it get flush from a call to devcd_free() - * mentioned as below. - * - * disabled_store() - * devcd_free() - * mutex_lock() devcd_data_write() - * flush_delayed_work() - * mutex_unlock() - * mutex_lock() - * mod_delayed_work() - * mutex_unlock() - * So, delete_work flag is required. + * The second race involves multiple parallel invocations of devcd_free(), + * add a deleted flag so only 1 can call the destructor. */ struct mutex mutex; - bool delete_work; + bool init_completed, deleted; struct module *owner; ssize_t (*read)(char *buffer, loff_t offset, size_t count, void *data, size_t datalen); void (*free)(void *data); + /* + * If nothing interferes and device_add() was returns success, + * del_wk will destroy the device after the timer fires. + * + * Multiple userspace processes can interfere in the working of the timer: + * - Writing to the coredump will reschedule the timer to run immediately, + * if still armed. + * + * This is handled by using "if (cancel_delayed_work()) { + * schedule_delayed_work() }", to prevent re-arming after having + * been previously fired. + * - Writing to /sys/class/devcoredump/disabled will destroy the + * coredump synchronously. + * This is handled by using disable_delayed_work_sync(), and then + * checking if deleted flag is set with &devcd->mutex held. + */ struct delayed_work del_wk; struct device *failing_dev; }; @@ -95,14 +91,27 @@ static void devcd_dev_release(struct device *dev) kfree(devcd); } +static void __devcd_del(struct devcd_entry *devcd) +{ + devcd->deleted = true; + device_del(&devcd->devcd_dev); + put_device(&devcd->devcd_dev); +} + static void devcd_del(struct work_struct *wk) { struct devcd_entry *devcd; + bool init_completed; devcd = container_of(wk, struct devcd_entry, del_wk.work); - device_del(&devcd->devcd_dev); - put_device(&devcd->devcd_dev); + /* devcd->mutex serializes against dev_coredumpm_timeout */ + mutex_lock(&devcd->mutex); + init_completed = devcd->init_completed; + mutex_unlock(&devcd->mutex); + + if (init_completed) + __devcd_del(devcd); } static ssize_t devcd_data_read(struct file *filp, struct kobject *kobj, @@ -122,12 +131,12 @@ static ssize_t devcd_data_write(struct file *filp, struct kobject *kobj, struct device *dev = kobj_to_dev(kobj); struct devcd_entry *devcd = dev_to_devcd(dev); - mutex_lock(&devcd->mutex); - if (!devcd->delete_work) { - devcd->delete_work = true; - mod_delayed_work(system_wq, &devcd->del_wk, 0); - } - mutex_unlock(&devcd->mutex); + /* + * Although it's tempting to use mod_delayed work here, + * that will cause a reschedule if the timer already fired. + */ + if (cancel_delayed_work(&devcd->del_wk)) + schedule_delayed_work(&devcd->del_wk, 0); return count; } @@ -151,11 +160,21 @@ static int devcd_free(struct device *dev, void *data) { struct devcd_entry *devcd = dev_to_devcd(dev); + /* + * To prevent a race with devcd_data_write(), disable work and + * complete manually instead. + * + * We cannot rely on the return value of + * disable_delayed_work_sync() here, because it might be in the + * middle of a cancel_delayed_work + schedule_delayed_work pair. + * + * devcd->mutex here guards against multiple parallel invocations + * of devcd_free(). + */ + disable_delayed_work_sync(&devcd->del_wk); mutex_lock(&devcd->mutex); - if (!devcd->delete_work) - devcd->delete_work = true; - - flush_delayed_work(&devcd->del_wk); + if (!devcd->deleted) + __devcd_del(devcd); mutex_unlock(&devcd->mutex); return 0; } @@ -179,12 +198,10 @@ static ssize_t disabled_show(const struct class *class, const struct class_attri * put_device() <- last reference * error = fn(dev, data) devcd_dev_release() * devcd_free(dev, data) kfree(devcd) - * mutex_lock(&devcd->mutex); * * * In the above diagram, it looks like disabled_store() would be racing with parallelly - * running devcd_del() and result in memory abort while acquiring devcd->mutex which - * is called after kfree of devcd memory after dropping its last reference with + * running devcd_del() and result in memory abort after dropping its last reference with * put_device(). However, this will not happens as fn(dev, data) runs * with its own reference to device via klist_node so it is not its last reference. * so, above situation would not occur. @@ -374,7 +391,7 @@ void dev_coredumpm_timeout(struct device *dev, struct module *owner, devcd->read = read; devcd->free = free; devcd->failing_dev = get_device(dev); - devcd->delete_work = false; + devcd->deleted = false; mutex_init(&devcd->mutex); device_initialize(&devcd->devcd_dev); @@ -383,8 +400,14 @@ void dev_coredumpm_timeout(struct device *dev, struct module *owner, atomic_inc_return(&devcd_count)); devcd->devcd_dev.class = &devcd_class; - mutex_lock(&devcd->mutex); dev_set_uevent_suppress(&devcd->devcd_dev, true); + + /* devcd->mutex prevents devcd_del() completing until init finishes */ + mutex_lock(&devcd->mutex); + devcd->init_completed = false; + INIT_DELAYED_WORK(&devcd->del_wk, devcd_del); + schedule_delayed_work(&devcd->del_wk, timeout); + if (device_add(&devcd->devcd_dev)) goto put_device; @@ -401,13 +424,20 @@ void dev_coredumpm_timeout(struct device *dev, struct module *owner, dev_set_uevent_suppress(&devcd->devcd_dev, false); kobject_uevent(&devcd->devcd_dev.kobj, KOBJ_ADD); - INIT_DELAYED_WORK(&devcd->del_wk, devcd_del); - schedule_delayed_work(&devcd->del_wk, timeout); + + /* + * Safe to run devcd_del() now that we are done with devcd_dev. + * Alternatively we could have taken a ref on devcd_dev before + * dropping the lock. + */ + devcd->init_completed = true; mutex_unlock(&devcd->mutex); return; put_device: - put_device(&devcd->devcd_dev); mutex_unlock(&devcd->mutex); + cancel_delayed_work_sync(&devcd->del_wk); + put_device(&devcd->devcd_dev); + put_module: module_put(owner); free:

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