Hi,
We (Ateme, a video encoding company) may have found an unwanted behavior in the scheduler since 5.10 (commit 16b0a7a1a0af), then 5.16 (commit c5b0a7eefc70), then 5.19 (commit not found yet), then maybe some other commits from 5.19 to 6.12, with a consequence of IPC decrease. Problem still appears on lasts 6.12, 6.13 and 6.14
We have reverted both 16b0a7a1a0af and c5b0a7eefc70 commits that reduce our performances (see fair.patch attached, applicable on 6.12.17). Performances increase but still doesnt reach our reference on 5.4.152.
Instead of trying to find every single commits from 5.18 to 6.12 that could decrease our performance, I chosed to bench 5.4.152 versus 6.12.17 with and without fair.patch.
The problem appeared clear : a lot of CPU migrations go out of CCX, then L3 miss, then IPC decrease.
Context of our bench: video decoder which work at a regulated speed, 1 process, 21 main threads, everyone of them creates 10 threads, 8 of them have a fine granularity, meaning they go to sleep quite often, giving the scheduler a lot of opportunities to act).
Hardware is an AMD Epyc 7702P, 128 cores, grouped by shared LLC 4 cores +4 hyperthreaded cores. NUMA topology is set by the BIOS to 1 node per socket.
Every pthread are created with default attributes.
I use AMDuProf (-C -A system -a -m ipc,l1,l2,l3,memory) for CPU Utilization (%), CPU effective freq, IPC, L2 access (pti), L2 miss (pti), L3 miss (absolute) and Mem (GB/s, and perf (stat -d -d -d -a) for Context switches, CPU migrations and Real time (s).
We noted that upgrade 5.4.152 to 6.12.17 without any special preempt configuration :
Two fold increase in CPU migration
30% memory bandwidth increase
20% L3 cache misses increase
10% IPC decrease
With the attached fair.patch applied to 6.12.17 (reminder : this patch reverts one commit appeared in 5.10 and another in 5.16) we managed to reduce CPU migrations and increase IPC but not as much as we had on 5.4.152. Our goal is to keep kernel "clean" without any patch (we don't want to apply and maintain fair.patch) then for the rest of my email we will consider stock kernel 6.12.17.
I've reduced the "sub threads count" to stays below 128 threads. Then still 21 main threads and instead of 10 worker per main thread I set 5 workers (4 of them with fine granularity) giving 105 pthreads -> everything goes fine in 6.12.17, no extra CPU migration, no extra memory bandwidth...
But as soon as we increase worker threads count (10 instead of 5) the problem appears.
We know our decoder may have too many threads but that's out of our scope, it has been designed like that some years ago and moving from "lot of small threads to few of big thread" is for now not possible.
We have a work around : we group threads using pthread affinities. Every main thread (and by inheritance of affinities every worker threads) on a single CCX so we reduce the L3 miss for them, then decrease memory bandwidth, then finally increasing IPC.
With that solution, we go above our original performances, for both kernels, and they perform at the same level. However, it is impractical to productize as such.
I've tried many kernel build configurations (CONFIG_PREMPT_*, CONFIG_SCHEDULER_*, tuning of fair.c:sysctl_sched_migration_cost) on 6.12.17, 6.12.21 (longterm), 6.13.9 (mainline), and 6.14.0 Nothing changes.
Q: Is there anyway to tune the kernel so we can get our performance back without using the pthread affinities work around ?
Feel free to ask an archive containing binaries and payload.
I first posted on https://bugzilla.kernel.org/show_bug.cgi?id=220000 but one told me the best way to get answers where these mailing lists
Regards,
Jean-Baptiste Roquefere, Ateme
Attached bench.tar.gz :
* bench/fair.patch
* bench/bench.ods with 2 sheets :
- regulated : decoder speed is regulated to keep real time constant
- no regul : decoder speed is not regulated and uses from 1 to 76 main threads with 10 worker per main thread
* bench/regulated.csv : bench.ods:regulated exported in csv format
* bench/not-regulated : bench.ods:no regul exported in csv format
Users of the Lenovo ThinkPad X13s have reported that Wi-Fi sometimes
breaks and the log fills up with errors like:
ath11k_pci 0006:01:00.0: HTC Rx: insufficient length, got 1484, expected 1492
ath11k_pci 0006:01:00.0: HTC Rx: insufficient length, got 1460, expected 1484
which based on a quick look at the ath11k driver seemed to indicate some
kind of ring-buffer corruption.
Miaoqing Pan tracked it down to the host seeing the updated destination
ring head pointer before the updated descriptor, and the error handling
for that in turn leaves the ring buffer in an inconsistent state.
While this has not yet been observed with ath12k, the ring-buffer
implementation is very similar to the ath11k one and it suffers from the
same bugs.
Add the missing memory barrier to make sure that the descriptor is read
after the head pointer to address the root cause of the corruption while
fixing up the error handling in case there are ever any (ordering) bugs
on the device side.
Note that the READ_ONCE() are only needed to avoid compiler mischief in
case the ring-buffer helpers are ever inlined.
Tested-on: WCN7850 hw2.0 WLAN.HMT.1.0.c5-00481-QCAHMTSWPL_V1.0_V2.0_SILICONZ-3
Fixes: d889913205cf ("wifi: ath12k: driver for Qualcomm Wi-Fi 7 devices")
Cc: stable(a)vger.kernel.org # 6.3
Link: https://bugzilla.kernel.org/show_bug.cgi?id=218623
Link: https://lore.kernel.org/20250310010217.3845141-3-quic_miaoqing@quicinc.com
Cc: Miaoqing Pan <quic_miaoqing(a)quicinc.com>
Signed-off-by: Johan Hovold <johan+linaro(a)kernel.org>
---
drivers/net/wireless/ath/ath12k/ce.c | 11 +++++------
drivers/net/wireless/ath/ath12k/hal.c | 4 ++--
2 files changed, 7 insertions(+), 8 deletions(-)
diff --git a/drivers/net/wireless/ath/ath12k/ce.c b/drivers/net/wireless/ath/ath12k/ce.c
index be0d669d31fc..740586fe49d1 100644
--- a/drivers/net/wireless/ath/ath12k/ce.c
+++ b/drivers/net/wireless/ath/ath12k/ce.c
@@ -343,11 +343,10 @@ static int ath12k_ce_completed_recv_next(struct ath12k_ce_pipe *pipe,
goto err;
}
+ /* Make sure descriptor is read after the head pointer. */
+ dma_rmb();
+
*nbytes = ath12k_hal_ce_dst_status_get_length(desc);
- if (*nbytes == 0) {
- ret = -EIO;
- goto err;
- }
*skb = pipe->dest_ring->skb[sw_index];
pipe->dest_ring->skb[sw_index] = NULL;
@@ -380,8 +379,8 @@ static void ath12k_ce_recv_process_cb(struct ath12k_ce_pipe *pipe)
dma_unmap_single(ab->dev, ATH12K_SKB_RXCB(skb)->paddr,
max_nbytes, DMA_FROM_DEVICE);
- if (unlikely(max_nbytes < nbytes)) {
- ath12k_warn(ab, "rxed more than expected (nbytes %d, max %d)",
+ if (unlikely(max_nbytes < nbytes || nbytes == 0)) {
+ ath12k_warn(ab, "unexpected rx length (nbytes %d, max %d)",
nbytes, max_nbytes);
dev_kfree_skb_any(skb);
continue;
diff --git a/drivers/net/wireless/ath/ath12k/hal.c b/drivers/net/wireless/ath/ath12k/hal.c
index cd59ff8e6c7b..91d5126ca149 100644
--- a/drivers/net/wireless/ath/ath12k/hal.c
+++ b/drivers/net/wireless/ath/ath12k/hal.c
@@ -1962,7 +1962,7 @@ u32 ath12k_hal_ce_dst_status_get_length(struct hal_ce_srng_dst_status_desc *desc
{
u32 len;
- len = le32_get_bits(desc->flags, HAL_CE_DST_STATUS_DESC_FLAGS_LEN);
+ len = le32_get_bits(READ_ONCE(desc->flags), HAL_CE_DST_STATUS_DESC_FLAGS_LEN);
desc->flags &= ~cpu_to_le32(HAL_CE_DST_STATUS_DESC_FLAGS_LEN);
return len;
@@ -2132,7 +2132,7 @@ void ath12k_hal_srng_access_begin(struct ath12k_base *ab, struct hal_srng *srng)
srng->u.src_ring.cached_tp =
*(volatile u32 *)srng->u.src_ring.tp_addr;
else
- srng->u.dst_ring.cached_hp = *srng->u.dst_ring.hp_addr;
+ srng->u.dst_ring.cached_hp = READ_ONCE(*srng->u.dst_ring.hp_addr);
}
/* Update cached ring head/tail pointers to HW. ath12k_hal_srng_access_begin()
--
2.48.1
The xHC resources allocated for USB devices are not released in correct
order after resuming in case when while suspend device was reconnected.
This issue has been detected during the fallowing scenario:
- connect hub HS to root port
- connect LS/FS device to hub port
- wait for enumeration to finish
- force host to suspend
- reconnect hub attached to root port
- wake host
For this scenario during enumeration of USB LS/FS device the Cadence xHC
reports completion error code for xHC commands because the xHC resources
used for devices has not been properly released.
XHCI specification doesn't mention that device can be reset in any order
so, we should not treat this issue as Cadence xHC controller bug.
Similar as during disconnecting in this case the device resources should
be cleared starting form the last usb device in tree toward the root hub.
To fix this issue usbcore driver should call hcd->driver->reset_device
for all USB devices connected to hub which was reconnected while
suspending.
Fixes: 3d82904559f4 ("usb: cdnsp: cdns3 Add main part of Cadence USBSSP DRD Driver")
cc: <stable(a)vger.kernel.org>
Signed-off-by: Pawel Laszczak <pawell(a)cadence.com>
---
Changelog:
v3:
- Changed patch title
- Corrected typo
- Moved hub_hc_release_resources above mutex_lock(hcd->address0_mutex)
v2:
- Replaced disconnection procedure with releasing only the xHC resources
drivers/usb/core/hub.c | 33 +++++++++++++++++++++++++++++++++
1 file changed, 33 insertions(+)
diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index a76bb50b6202..dcba4281ea48 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -6065,6 +6065,36 @@ void usb_hub_cleanup(void)
usb_deregister(&hub_driver);
} /* usb_hub_cleanup() */
+/**
+ * hub_hc_release_resources - clear resources used by host controller
+ * @udev: pointer to device being released
+ *
+ * Context: task context, might sleep
+ *
+ * Function releases the host controller resources in correct order before
+ * making any operation on resuming usb device. The host controller resources
+ * allocated for devices in tree should be released starting from the last
+ * usb device in tree toward the root hub. This function is used only during
+ * resuming device when usb device require reinitialization – that is, when
+ * flag udev->reset_resume is set.
+ *
+ * This call is synchronous, and may not be used in an interrupt context.
+ */
+static void hub_hc_release_resources(struct usb_device *udev)
+{
+ struct usb_hub *hub = usb_hub_to_struct_hub(udev);
+ struct usb_hcd *hcd = bus_to_hcd(udev->bus);
+ int i;
+
+ /* Release up resources for all children before this device */
+ for (i = 0; i < udev->maxchild; i++)
+ if (hub->ports[i]->child)
+ hub_hc_release_resources(hub->ports[i]->child);
+
+ if (hcd->driver->reset_device)
+ hcd->driver->reset_device(hcd, udev);
+}
+
/**
* usb_reset_and_verify_device - perform a USB port reset to reinitialize a device
* @udev: device to reset (not in SUSPENDED or NOTATTACHED state)
@@ -6129,6 +6159,9 @@ static int usb_reset_and_verify_device(struct usb_device *udev)
bos = udev->bos;
udev->bos = NULL;
+ if (udev->reset_resume)
+ hub_hc_release_resources(udev);
+
mutex_lock(hcd->address0_mutex);
for (i = 0; i < PORT_INIT_TRIES; ++i) {
--
2.43.0
The patch below does not apply to the 6.6-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-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 53dac345395c0d2493cbc2f4c85fe38aef5b63f5
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable(a)vger.kernel.org>' --in-reply-to '2025021052-avenging-aflutter-192c@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 53dac345395c0d2493cbc2f4c85fe38aef5b63f5 Mon Sep 17 00:00:00 2001
From: Frederic Weisbecker <frederic(a)kernel.org>
Date: Sat, 18 Jan 2025 00:24:33 +0100
Subject: [PATCH] hrtimers: Force migrate away hrtimers queued after
CPUHP_AP_HRTIMERS_DYING
hrtimers are migrated away from the dying CPU to any online target at
the CPUHP_AP_HRTIMERS_DYING stage in order not to delay bandwidth timers
handling tasks involved in the CPU hotplug forward progress.
However wakeups can still be performed by the outgoing CPU after
CPUHP_AP_HRTIMERS_DYING. Those can result again in bandwidth timers being
armed. Depending on several considerations (crystal ball power management
based election, earliest timer already enqueued, timer migration enabled or
not), the target may eventually be the current CPU even if offline. If that
happens, the timer is eventually ignored.
The most notable example is RCU which had to deal with each and every of
those wake-ups by deferring them to an online CPU, along with related
workarounds:
_ e787644caf76 (rcu: Defer RCU kthreads wakeup when CPU is dying)
_ 9139f93209d1 (rcu/nocb: Fix RT throttling hrtimer armed from offline CPU)
_ f7345ccc62a4 (rcu/nocb: Fix rcuog wake-up from offline softirq)
The problem isn't confined to RCU though as the stop machine kthread
(which runs CPUHP_AP_HRTIMERS_DYING) reports its completion at the end
of its work through cpu_stop_signal_done() and performs a wake up that
eventually arms the deadline server timer:
WARNING: CPU: 94 PID: 588 at kernel/time/hrtimer.c:1086 hrtimer_start_range_ns+0x289/0x2d0
CPU: 94 UID: 0 PID: 588 Comm: migration/94 Not tainted
Stopper: multi_cpu_stop+0x0/0x120 <- stop_machine_cpuslocked+0x66/0xc0
RIP: 0010:hrtimer_start_range_ns+0x289/0x2d0
Call Trace:
<TASK>
start_dl_timer
enqueue_dl_entity
dl_server_start
enqueue_task_fair
enqueue_task
ttwu_do_activate
try_to_wake_up
complete
cpu_stopper_thread
Instead of providing yet another bandaid to work around the situation, fix
it in the hrtimers infrastructure instead: always migrate away a timer to
an online target whenever it is enqueued from an offline CPU.
This will also allow to revert all the above RCU disgraceful hacks.
Fixes: 5c0930ccaad5 ("hrtimers: Push pending hrtimers away from outgoing CPU earlier")
Reported-by: Vlad Poenaru <vlad.wing(a)gmail.com>
Reported-by: Usama Arif <usamaarif642(a)gmail.com>
Signed-off-by: Frederic Weisbecker <frederic(a)kernel.org>
Signed-off-by: Paul E. McKenney <paulmck(a)kernel.org>
Signed-off-by: Thomas Gleixner <tglx(a)linutronix.de>
Cc: stable(a)vger.kernel.org
Tested-by: Paul E. McKenney <paulmck(a)kernel.org>
Link: https://lore.kernel.org/all/20250117232433.24027-1-frederic@kernel.org
Closes: 20241213203739.1519801-1-usamaarif642(a)gmail.com
diff --git a/include/linux/hrtimer_defs.h b/include/linux/hrtimer_defs.h
index c3b4b7ed7c16..84a5045f80f3 100644
--- a/include/linux/hrtimer_defs.h
+++ b/include/linux/hrtimer_defs.h
@@ -125,6 +125,7 @@ struct hrtimer_cpu_base {
ktime_t softirq_expires_next;
struct hrtimer *softirq_next_timer;
struct hrtimer_clock_base clock_base[HRTIMER_MAX_CLOCK_BASES];
+ call_single_data_t csd;
} ____cacheline_aligned;
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 4fb81f8c6f1c..deb1aa32814e 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -58,6 +58,8 @@
#define HRTIMER_ACTIVE_SOFT (HRTIMER_ACTIVE_HARD << MASK_SHIFT)
#define HRTIMER_ACTIVE_ALL (HRTIMER_ACTIVE_SOFT | HRTIMER_ACTIVE_HARD)
+static void retrigger_next_event(void *arg);
+
/*
* The timer bases:
*
@@ -111,7 +113,8 @@ DEFINE_PER_CPU(struct hrtimer_cpu_base, hrtimer_bases) =
.clockid = CLOCK_TAI,
.get_time = &ktime_get_clocktai,
},
- }
+ },
+ .csd = CSD_INIT(retrigger_next_event, NULL)
};
static const int hrtimer_clock_to_base_table[MAX_CLOCKS] = {
@@ -124,6 +127,14 @@ static const int hrtimer_clock_to_base_table[MAX_CLOCKS] = {
[CLOCK_TAI] = HRTIMER_BASE_TAI,
};
+static inline bool hrtimer_base_is_online(struct hrtimer_cpu_base *base)
+{
+ if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
+ return true;
+ else
+ return likely(base->online);
+}
+
/*
* Functions and macros which are different for UP/SMP systems are kept in a
* single place
@@ -178,27 +189,54 @@ struct hrtimer_clock_base *lock_hrtimer_base(const struct hrtimer *timer,
}
/*
- * We do not migrate the timer when it is expiring before the next
- * event on the target cpu. When high resolution is enabled, we cannot
- * reprogram the target cpu hardware and we would cause it to fire
- * late. To keep it simple, we handle the high resolution enabled and
- * disabled case similar.
+ * Check if the elected target is suitable considering its next
+ * event and the hotplug state of the current CPU.
+ *
+ * If the elected target is remote and its next event is after the timer
+ * to queue, then a remote reprogram is necessary. However there is no
+ * guarantee the IPI handling the operation would arrive in time to meet
+ * the high resolution deadline. In this case the local CPU becomes a
+ * preferred target, unless it is offline.
+ *
+ * High and low resolution modes are handled the same way for simplicity.
*
* Called with cpu_base->lock of target cpu held.
*/
-static int
-hrtimer_check_target(struct hrtimer *timer, struct hrtimer_clock_base *new_base)
+static bool hrtimer_suitable_target(struct hrtimer *timer, struct hrtimer_clock_base *new_base,
+ struct hrtimer_cpu_base *new_cpu_base,
+ struct hrtimer_cpu_base *this_cpu_base)
{
ktime_t expires;
+ /*
+ * The local CPU clockevent can be reprogrammed. Also get_target_base()
+ * guarantees it is online.
+ */
+ if (new_cpu_base == this_cpu_base)
+ return true;
+
+ /*
+ * The offline local CPU can't be the default target if the
+ * next remote target event is after this timer. Keep the
+ * elected new base. An IPI will we issued to reprogram
+ * it as a last resort.
+ */
+ if (!hrtimer_base_is_online(this_cpu_base))
+ return true;
+
expires = ktime_sub(hrtimer_get_expires(timer), new_base->offset);
- return expires < new_base->cpu_base->expires_next;
+
+ return expires >= new_base->cpu_base->expires_next;
}
-static inline
-struct hrtimer_cpu_base *get_target_base(struct hrtimer_cpu_base *base,
- int pinned)
+static inline struct hrtimer_cpu_base *get_target_base(struct hrtimer_cpu_base *base, int pinned)
{
+ if (!hrtimer_base_is_online(base)) {
+ int cpu = cpumask_any_and(cpu_online_mask, housekeeping_cpumask(HK_TYPE_TIMER));
+
+ return &per_cpu(hrtimer_bases, cpu);
+ }
+
#if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON)
if (static_branch_likely(&timers_migration_enabled) && !pinned)
return &per_cpu(hrtimer_bases, get_nohz_timer_target());
@@ -249,8 +287,8 @@ switch_hrtimer_base(struct hrtimer *timer, struct hrtimer_clock_base *base,
raw_spin_unlock(&base->cpu_base->lock);
raw_spin_lock(&new_base->cpu_base->lock);
- if (new_cpu_base != this_cpu_base &&
- hrtimer_check_target(timer, new_base)) {
+ if (!hrtimer_suitable_target(timer, new_base, new_cpu_base,
+ this_cpu_base)) {
raw_spin_unlock(&new_base->cpu_base->lock);
raw_spin_lock(&base->cpu_base->lock);
new_cpu_base = this_cpu_base;
@@ -259,8 +297,7 @@ switch_hrtimer_base(struct hrtimer *timer, struct hrtimer_clock_base *base,
}
WRITE_ONCE(timer->base, new_base);
} else {
- if (new_cpu_base != this_cpu_base &&
- hrtimer_check_target(timer, new_base)) {
+ if (!hrtimer_suitable_target(timer, new_base, new_cpu_base, this_cpu_base)) {
new_cpu_base = this_cpu_base;
goto again;
}
@@ -706,8 +743,6 @@ static inline int hrtimer_is_hres_enabled(void)
return hrtimer_hres_enabled;
}
-static void retrigger_next_event(void *arg);
-
/*
* Switch to high resolution mode
*/
@@ -1195,6 +1230,7 @@ static int __hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim,
u64 delta_ns, const enum hrtimer_mode mode,
struct hrtimer_clock_base *base)
{
+ struct hrtimer_cpu_base *this_cpu_base = this_cpu_ptr(&hrtimer_bases);
struct hrtimer_clock_base *new_base;
bool force_local, first;
@@ -1206,9 +1242,15 @@ static int __hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim,
* and enforce reprogramming after it is queued no matter whether
* it is the new first expiring timer again or not.
*/
- force_local = base->cpu_base == this_cpu_ptr(&hrtimer_bases);
+ force_local = base->cpu_base == this_cpu_base;
force_local &= base->cpu_base->next_timer == timer;
+ /*
+ * Don't force local queuing if this enqueue happens on a unplugged
+ * CPU after hrtimer_cpu_dying() has been invoked.
+ */
+ force_local &= this_cpu_base->online;
+
/*
* Remove an active timer from the queue. In case it is not queued
* on the current CPU, make sure that remove_hrtimer() updates the
@@ -1238,8 +1280,27 @@ static int __hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim,
}
first = enqueue_hrtimer(timer, new_base, mode);
- if (!force_local)
- return first;
+ if (!force_local) {
+ /*
+ * If the current CPU base is online, then the timer is
+ * never queued on a remote CPU if it would be the first
+ * expiring timer there.
+ */
+ if (hrtimer_base_is_online(this_cpu_base))
+ return first;
+
+ /*
+ * Timer was enqueued remote because the current base is
+ * already offline. If the timer is the first to expire,
+ * kick the remote CPU to reprogram the clock event.
+ */
+ if (first) {
+ struct hrtimer_cpu_base *new_cpu_base = new_base->cpu_base;
+
+ smp_call_function_single_async(new_cpu_base->cpu, &new_cpu_base->csd);
+ }
+ return 0;
+ }
/*
* Timer was forced to stay on the current CPU to avoid
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 53dac345395c0d2493cbc2f4c85fe38aef5b63f5
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable(a)vger.kernel.org>' --in-reply-to '2025021053-unranked-silt-0282@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 53dac345395c0d2493cbc2f4c85fe38aef5b63f5 Mon Sep 17 00:00:00 2001
From: Frederic Weisbecker <frederic(a)kernel.org>
Date: Sat, 18 Jan 2025 00:24:33 +0100
Subject: [PATCH] hrtimers: Force migrate away hrtimers queued after
CPUHP_AP_HRTIMERS_DYING
hrtimers are migrated away from the dying CPU to any online target at
the CPUHP_AP_HRTIMERS_DYING stage in order not to delay bandwidth timers
handling tasks involved in the CPU hotplug forward progress.
However wakeups can still be performed by the outgoing CPU after
CPUHP_AP_HRTIMERS_DYING. Those can result again in bandwidth timers being
armed. Depending on several considerations (crystal ball power management
based election, earliest timer already enqueued, timer migration enabled or
not), the target may eventually be the current CPU even if offline. If that
happens, the timer is eventually ignored.
The most notable example is RCU which had to deal with each and every of
those wake-ups by deferring them to an online CPU, along with related
workarounds:
_ e787644caf76 (rcu: Defer RCU kthreads wakeup when CPU is dying)
_ 9139f93209d1 (rcu/nocb: Fix RT throttling hrtimer armed from offline CPU)
_ f7345ccc62a4 (rcu/nocb: Fix rcuog wake-up from offline softirq)
The problem isn't confined to RCU though as the stop machine kthread
(which runs CPUHP_AP_HRTIMERS_DYING) reports its completion at the end
of its work through cpu_stop_signal_done() and performs a wake up that
eventually arms the deadline server timer:
WARNING: CPU: 94 PID: 588 at kernel/time/hrtimer.c:1086 hrtimer_start_range_ns+0x289/0x2d0
CPU: 94 UID: 0 PID: 588 Comm: migration/94 Not tainted
Stopper: multi_cpu_stop+0x0/0x120 <- stop_machine_cpuslocked+0x66/0xc0
RIP: 0010:hrtimer_start_range_ns+0x289/0x2d0
Call Trace:
<TASK>
start_dl_timer
enqueue_dl_entity
dl_server_start
enqueue_task_fair
enqueue_task
ttwu_do_activate
try_to_wake_up
complete
cpu_stopper_thread
Instead of providing yet another bandaid to work around the situation, fix
it in the hrtimers infrastructure instead: always migrate away a timer to
an online target whenever it is enqueued from an offline CPU.
This will also allow to revert all the above RCU disgraceful hacks.
Fixes: 5c0930ccaad5 ("hrtimers: Push pending hrtimers away from outgoing CPU earlier")
Reported-by: Vlad Poenaru <vlad.wing(a)gmail.com>
Reported-by: Usama Arif <usamaarif642(a)gmail.com>
Signed-off-by: Frederic Weisbecker <frederic(a)kernel.org>
Signed-off-by: Paul E. McKenney <paulmck(a)kernel.org>
Signed-off-by: Thomas Gleixner <tglx(a)linutronix.de>
Cc: stable(a)vger.kernel.org
Tested-by: Paul E. McKenney <paulmck(a)kernel.org>
Link: https://lore.kernel.org/all/20250117232433.24027-1-frederic@kernel.org
Closes: 20241213203739.1519801-1-usamaarif642(a)gmail.com
diff --git a/include/linux/hrtimer_defs.h b/include/linux/hrtimer_defs.h
index c3b4b7ed7c16..84a5045f80f3 100644
--- a/include/linux/hrtimer_defs.h
+++ b/include/linux/hrtimer_defs.h
@@ -125,6 +125,7 @@ struct hrtimer_cpu_base {
ktime_t softirq_expires_next;
struct hrtimer *softirq_next_timer;
struct hrtimer_clock_base clock_base[HRTIMER_MAX_CLOCK_BASES];
+ call_single_data_t csd;
} ____cacheline_aligned;
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 4fb81f8c6f1c..deb1aa32814e 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -58,6 +58,8 @@
#define HRTIMER_ACTIVE_SOFT (HRTIMER_ACTIVE_HARD << MASK_SHIFT)
#define HRTIMER_ACTIVE_ALL (HRTIMER_ACTIVE_SOFT | HRTIMER_ACTIVE_HARD)
+static void retrigger_next_event(void *arg);
+
/*
* The timer bases:
*
@@ -111,7 +113,8 @@ DEFINE_PER_CPU(struct hrtimer_cpu_base, hrtimer_bases) =
.clockid = CLOCK_TAI,
.get_time = &ktime_get_clocktai,
},
- }
+ },
+ .csd = CSD_INIT(retrigger_next_event, NULL)
};
static const int hrtimer_clock_to_base_table[MAX_CLOCKS] = {
@@ -124,6 +127,14 @@ static const int hrtimer_clock_to_base_table[MAX_CLOCKS] = {
[CLOCK_TAI] = HRTIMER_BASE_TAI,
};
+static inline bool hrtimer_base_is_online(struct hrtimer_cpu_base *base)
+{
+ if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
+ return true;
+ else
+ return likely(base->online);
+}
+
/*
* Functions and macros which are different for UP/SMP systems are kept in a
* single place
@@ -178,27 +189,54 @@ struct hrtimer_clock_base *lock_hrtimer_base(const struct hrtimer *timer,
}
/*
- * We do not migrate the timer when it is expiring before the next
- * event on the target cpu. When high resolution is enabled, we cannot
- * reprogram the target cpu hardware and we would cause it to fire
- * late. To keep it simple, we handle the high resolution enabled and
- * disabled case similar.
+ * Check if the elected target is suitable considering its next
+ * event and the hotplug state of the current CPU.
+ *
+ * If the elected target is remote and its next event is after the timer
+ * to queue, then a remote reprogram is necessary. However there is no
+ * guarantee the IPI handling the operation would arrive in time to meet
+ * the high resolution deadline. In this case the local CPU becomes a
+ * preferred target, unless it is offline.
+ *
+ * High and low resolution modes are handled the same way for simplicity.
*
* Called with cpu_base->lock of target cpu held.
*/
-static int
-hrtimer_check_target(struct hrtimer *timer, struct hrtimer_clock_base *new_base)
+static bool hrtimer_suitable_target(struct hrtimer *timer, struct hrtimer_clock_base *new_base,
+ struct hrtimer_cpu_base *new_cpu_base,
+ struct hrtimer_cpu_base *this_cpu_base)
{
ktime_t expires;
+ /*
+ * The local CPU clockevent can be reprogrammed. Also get_target_base()
+ * guarantees it is online.
+ */
+ if (new_cpu_base == this_cpu_base)
+ return true;
+
+ /*
+ * The offline local CPU can't be the default target if the
+ * next remote target event is after this timer. Keep the
+ * elected new base. An IPI will we issued to reprogram
+ * it as a last resort.
+ */
+ if (!hrtimer_base_is_online(this_cpu_base))
+ return true;
+
expires = ktime_sub(hrtimer_get_expires(timer), new_base->offset);
- return expires < new_base->cpu_base->expires_next;
+
+ return expires >= new_base->cpu_base->expires_next;
}
-static inline
-struct hrtimer_cpu_base *get_target_base(struct hrtimer_cpu_base *base,
- int pinned)
+static inline struct hrtimer_cpu_base *get_target_base(struct hrtimer_cpu_base *base, int pinned)
{
+ if (!hrtimer_base_is_online(base)) {
+ int cpu = cpumask_any_and(cpu_online_mask, housekeeping_cpumask(HK_TYPE_TIMER));
+
+ return &per_cpu(hrtimer_bases, cpu);
+ }
+
#if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON)
if (static_branch_likely(&timers_migration_enabled) && !pinned)
return &per_cpu(hrtimer_bases, get_nohz_timer_target());
@@ -249,8 +287,8 @@ switch_hrtimer_base(struct hrtimer *timer, struct hrtimer_clock_base *base,
raw_spin_unlock(&base->cpu_base->lock);
raw_spin_lock(&new_base->cpu_base->lock);
- if (new_cpu_base != this_cpu_base &&
- hrtimer_check_target(timer, new_base)) {
+ if (!hrtimer_suitable_target(timer, new_base, new_cpu_base,
+ this_cpu_base)) {
raw_spin_unlock(&new_base->cpu_base->lock);
raw_spin_lock(&base->cpu_base->lock);
new_cpu_base = this_cpu_base;
@@ -259,8 +297,7 @@ switch_hrtimer_base(struct hrtimer *timer, struct hrtimer_clock_base *base,
}
WRITE_ONCE(timer->base, new_base);
} else {
- if (new_cpu_base != this_cpu_base &&
- hrtimer_check_target(timer, new_base)) {
+ if (!hrtimer_suitable_target(timer, new_base, new_cpu_base, this_cpu_base)) {
new_cpu_base = this_cpu_base;
goto again;
}
@@ -706,8 +743,6 @@ static inline int hrtimer_is_hres_enabled(void)
return hrtimer_hres_enabled;
}
-static void retrigger_next_event(void *arg);
-
/*
* Switch to high resolution mode
*/
@@ -1195,6 +1230,7 @@ static int __hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim,
u64 delta_ns, const enum hrtimer_mode mode,
struct hrtimer_clock_base *base)
{
+ struct hrtimer_cpu_base *this_cpu_base = this_cpu_ptr(&hrtimer_bases);
struct hrtimer_clock_base *new_base;
bool force_local, first;
@@ -1206,9 +1242,15 @@ static int __hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim,
* and enforce reprogramming after it is queued no matter whether
* it is the new first expiring timer again or not.
*/
- force_local = base->cpu_base == this_cpu_ptr(&hrtimer_bases);
+ force_local = base->cpu_base == this_cpu_base;
force_local &= base->cpu_base->next_timer == timer;
+ /*
+ * Don't force local queuing if this enqueue happens on a unplugged
+ * CPU after hrtimer_cpu_dying() has been invoked.
+ */
+ force_local &= this_cpu_base->online;
+
/*
* Remove an active timer from the queue. In case it is not queued
* on the current CPU, make sure that remove_hrtimer() updates the
@@ -1238,8 +1280,27 @@ static int __hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim,
}
first = enqueue_hrtimer(timer, new_base, mode);
- if (!force_local)
- return first;
+ if (!force_local) {
+ /*
+ * If the current CPU base is online, then the timer is
+ * never queued on a remote CPU if it would be the first
+ * expiring timer there.
+ */
+ if (hrtimer_base_is_online(this_cpu_base))
+ return first;
+
+ /*
+ * Timer was enqueued remote because the current base is
+ * already offline. If the timer is the first to expire,
+ * kick the remote CPU to reprogram the clock event.
+ */
+ if (first) {
+ struct hrtimer_cpu_base *new_cpu_base = new_base->cpu_base;
+
+ smp_call_function_single_async(new_cpu_base->cpu, &new_cpu_base->csd);
+ }
+ return 0;
+ }
/*
* Timer was forced to stay on the current CPU to avoid
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 3e74859ee35edc33a022c3f3971df066ea0ca6b9
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable(a)vger.kernel.org>' --in-reply-to '2024123045-parka-sublet-a95d@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 3e74859ee35edc33a022c3f3971df066ea0ca6b9 Mon Sep 17 00:00:00 2001
From: Boris Burkov <boris(a)bur.io>
Date: Fri, 13 Dec 2024 12:22:32 -0800
Subject: [PATCH] btrfs: check folio mapping after unlock in
relocate_one_folio()
When we call btrfs_read_folio() to bring a folio uptodate, we unlock the
folio. The result of that is that a different thread can modify the
mapping (like remove it with invalidate) before we call folio_lock().
This results in an invalid page and we need to try again.
In particular, if we are relocating concurrently with aborting a
transaction, this can result in a crash like the following:
BUG: kernel NULL pointer dereference, address: 0000000000000000
PGD 0 P4D 0
Oops: 0000 [#1] SMP
CPU: 76 PID: 1411631 Comm: kworker/u322:5
Workqueue: events_unbound btrfs_reclaim_bgs_work
RIP: 0010:set_page_extent_mapped+0x20/0xb0
RSP: 0018:ffffc900516a7be8 EFLAGS: 00010246
RAX: ffffea009e851d08 RBX: ffffea009e0b1880 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffc900516a7b90 RDI: ffffea009e0b1880
RBP: 0000000003573000 R08: 0000000000000001 R09: ffff88c07fd2f3f0
R10: 0000000000000000 R11: 0000194754b575be R12: 0000000003572000
R13: 0000000003572fff R14: 0000000000100cca R15: 0000000005582fff
FS: 0000000000000000(0000) GS:ffff88c07fd00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000407d00f002 CR4: 00000000007706f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
PKRU: 55555554
Call Trace:
<TASK>
? __die+0x78/0xc0
? page_fault_oops+0x2a8/0x3a0
? __switch_to+0x133/0x530
? wq_worker_running+0xa/0x40
? exc_page_fault+0x63/0x130
? asm_exc_page_fault+0x22/0x30
? set_page_extent_mapped+0x20/0xb0
relocate_file_extent_cluster+0x1a7/0x940
relocate_data_extent+0xaf/0x120
relocate_block_group+0x20f/0x480
btrfs_relocate_block_group+0x152/0x320
btrfs_relocate_chunk+0x3d/0x120
btrfs_reclaim_bgs_work+0x2ae/0x4e0
process_scheduled_works+0x184/0x370
worker_thread+0xc6/0x3e0
? blk_add_timer+0xb0/0xb0
kthread+0xae/0xe0
? flush_tlb_kernel_range+0x90/0x90
ret_from_fork+0x2f/0x40
? flush_tlb_kernel_range+0x90/0x90
ret_from_fork_asm+0x11/0x20
</TASK>
This occurs because cleanup_one_transaction() calls
destroy_delalloc_inodes() which calls invalidate_inode_pages2() which
takes the folio_lock before setting mapping to NULL. We fail to check
this, and subsequently call set_extent_mapping(), which assumes that
mapping != NULL (in fact it asserts that in debug mode)
Note that the "fixes" patch here is not the one that introduced the
race (the very first iteration of this code from 2009) but a more recent
change that made this particular crash happen in practice.
Fixes: e7f1326cc24e ("btrfs: set page extent mapped after read_folio in relocate_one_page")
CC: stable(a)vger.kernel.org # 6.1+
Reviewed-by: Qu Wenruo <wqu(a)suse.com>
Signed-off-by: Boris Burkov <boris(a)bur.io>
Signed-off-by: David Sterba <dsterba(a)suse.com>
diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index bf267bdfa8f8..db8b42f674b7 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -2902,6 +2902,7 @@ static int relocate_one_folio(struct reloc_control *rc,
const bool use_rst = btrfs_need_stripe_tree_update(fs_info, rc->block_group->flags);
ASSERT(index <= last_index);
+again:
folio = filemap_lock_folio(inode->i_mapping, index);
if (IS_ERR(folio)) {
@@ -2937,6 +2938,11 @@ static int relocate_one_folio(struct reloc_control *rc,
ret = -EIO;
goto release_folio;
}
+ if (folio->mapping != inode->i_mapping) {
+ folio_unlock(folio);
+ folio_put(folio);
+ goto again;
+ }
}
/*
The patch below does not apply to the 6.6-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-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 3e74859ee35edc33a022c3f3971df066ea0ca6b9
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable(a)vger.kernel.org>' --in-reply-to '2024123042-limelight-doily-8703@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 3e74859ee35edc33a022c3f3971df066ea0ca6b9 Mon Sep 17 00:00:00 2001
From: Boris Burkov <boris(a)bur.io>
Date: Fri, 13 Dec 2024 12:22:32 -0800
Subject: [PATCH] btrfs: check folio mapping after unlock in
relocate_one_folio()
When we call btrfs_read_folio() to bring a folio uptodate, we unlock the
folio. The result of that is that a different thread can modify the
mapping (like remove it with invalidate) before we call folio_lock().
This results in an invalid page and we need to try again.
In particular, if we are relocating concurrently with aborting a
transaction, this can result in a crash like the following:
BUG: kernel NULL pointer dereference, address: 0000000000000000
PGD 0 P4D 0
Oops: 0000 [#1] SMP
CPU: 76 PID: 1411631 Comm: kworker/u322:5
Workqueue: events_unbound btrfs_reclaim_bgs_work
RIP: 0010:set_page_extent_mapped+0x20/0xb0
RSP: 0018:ffffc900516a7be8 EFLAGS: 00010246
RAX: ffffea009e851d08 RBX: ffffea009e0b1880 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffc900516a7b90 RDI: ffffea009e0b1880
RBP: 0000000003573000 R08: 0000000000000001 R09: ffff88c07fd2f3f0
R10: 0000000000000000 R11: 0000194754b575be R12: 0000000003572000
R13: 0000000003572fff R14: 0000000000100cca R15: 0000000005582fff
FS: 0000000000000000(0000) GS:ffff88c07fd00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000407d00f002 CR4: 00000000007706f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
PKRU: 55555554
Call Trace:
<TASK>
? __die+0x78/0xc0
? page_fault_oops+0x2a8/0x3a0
? __switch_to+0x133/0x530
? wq_worker_running+0xa/0x40
? exc_page_fault+0x63/0x130
? asm_exc_page_fault+0x22/0x30
? set_page_extent_mapped+0x20/0xb0
relocate_file_extent_cluster+0x1a7/0x940
relocate_data_extent+0xaf/0x120
relocate_block_group+0x20f/0x480
btrfs_relocate_block_group+0x152/0x320
btrfs_relocate_chunk+0x3d/0x120
btrfs_reclaim_bgs_work+0x2ae/0x4e0
process_scheduled_works+0x184/0x370
worker_thread+0xc6/0x3e0
? blk_add_timer+0xb0/0xb0
kthread+0xae/0xe0
? flush_tlb_kernel_range+0x90/0x90
ret_from_fork+0x2f/0x40
? flush_tlb_kernel_range+0x90/0x90
ret_from_fork_asm+0x11/0x20
</TASK>
This occurs because cleanup_one_transaction() calls
destroy_delalloc_inodes() which calls invalidate_inode_pages2() which
takes the folio_lock before setting mapping to NULL. We fail to check
this, and subsequently call set_extent_mapping(), which assumes that
mapping != NULL (in fact it asserts that in debug mode)
Note that the "fixes" patch here is not the one that introduced the
race (the very first iteration of this code from 2009) but a more recent
change that made this particular crash happen in practice.
Fixes: e7f1326cc24e ("btrfs: set page extent mapped after read_folio in relocate_one_page")
CC: stable(a)vger.kernel.org # 6.1+
Reviewed-by: Qu Wenruo <wqu(a)suse.com>
Signed-off-by: Boris Burkov <boris(a)bur.io>
Signed-off-by: David Sterba <dsterba(a)suse.com>
diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index bf267bdfa8f8..db8b42f674b7 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -2902,6 +2902,7 @@ static int relocate_one_folio(struct reloc_control *rc,
const bool use_rst = btrfs_need_stripe_tree_update(fs_info, rc->block_group->flags);
ASSERT(index <= last_index);
+again:
folio = filemap_lock_folio(inode->i_mapping, index);
if (IS_ERR(folio)) {
@@ -2937,6 +2938,11 @@ static int relocate_one_folio(struct reloc_control *rc,
ret = -EIO;
goto release_folio;
}
+ if (folio->mapping != inode->i_mapping) {
+ folio_unlock(folio);
+ folio_put(folio);
+ goto again;
+ }
}
/*