When the kernel panics, one page worth of kmsg data is written to an allocated page. The Hypervisor is notified of the page address trough the MSR. This panic information is collected on the host. Since we are only collecting one page of data, the full panic message may not be collected.
Each line of the panic message is prefixed with the log level of that particular message in the form <N>, where N is the log level. The typical 4 Kbytes contains anywhere from 50 to 100 lines with that log level prefix.
hv_dmsg_dump() makes a call to kmsg_dump_get_buffer(). The second argument in the call is a bool described as: ‘@syslog: include the “<4>” Prefixes’.
With this change, we will not write the log level to the allocated page. This will provide additional room in the allocated page for more informative panic information.
Requesting in stable kernels, since many kernels running in production are stable releases.
Cc: stable@vger.kernel.org Signed-off-by: Joseph Salisbury joseph.salisbury@microsoft.com --- drivers/hv/vmbus_drv.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c index 9147ee9d5f7d..d69f4efa3719 100644 --- a/drivers/hv/vmbus_drv.c +++ b/drivers/hv/vmbus_drv.c @@ -1368,7 +1368,7 @@ static void hv_kmsg_dump(struct kmsg_dumper *dumper, * Write dump contents to the page. No need to synchronize; panic should * be single-threaded. */ - kmsg_dump_get_buffer(dumper, true, hv_panic_page, HV_HYP_PAGE_SIZE, + kmsg_dump_get_buffer(dumper, false, hv_panic_page, HV_HYP_PAGE_SIZE, &bytes_written); if (bytes_written) hyperv_report_panic_msg(panic_pa, bytes_written);
From: Joseph Salisbury joseph.salisbury@microsoft.com Sent: Friday, June 26, 2020 10:48 AM
When the kernel panics, one page worth of kmsg data is written to an allocated page. The Hypervisor is notified of the page address trough the MSR. This panic information is collected on the host. Since we are only collecting one page of data, the full panic message may not be collected.
Each line of the panic message is prefixed with the log level of that particular message in the form <N>, where N is the log level. The typical 4 Kbytes contains anywhere from 50 to 100 lines with that log level prefix.
hv_dmsg_dump() makes a call to kmsg_dump_get_buffer(). The second argument in the call is a bool described as: ‘@syslog: include the “<4>” Prefixes’.
With this change, we will not write the log level to the allocated page. This will provide additional room in the allocated page for more informative panic information.
Let me suggest tightening the commit message a bit, with focus on the "what" and "why" rather than the details of the code change. Also use imperative voice per the Linux kernel guidelines:
When the kernel panics, one page of kmsg data may be collected and sent to Hyper-V to aid in diagnosing the failure. The collected kmsg data typically contains 50 to 100 lines, each of which has a log level prefix that isn't very useful from a diagnostic standpoint. So tell kmsg_dump_get_buffer() to not include the log level, enabling more information that *is* useful to fit in the page.
Requesting in stable kernels, since many kernels running in production are stable releases.
Cc: stable@vger.kernel.org Signed-off-by: Joseph Salisbury joseph.salisbury@microsoft.com
drivers/hv/vmbus_drv.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c index 9147ee9d5f7d..d69f4efa3719 100644 --- a/drivers/hv/vmbus_drv.c +++ b/drivers/hv/vmbus_drv.c @@ -1368,7 +1368,7 @@ static void hv_kmsg_dump(struct kmsg_dumper *dumper, * Write dump contents to the page. No need to synchronize; panic should * be single-threaded. */
- kmsg_dump_get_buffer(dumper, true, hv_panic_page, HV_HYP_PAGE_SIZE,
- kmsg_dump_get_buffer(dumper, false, hv_panic_page, HV_HYP_PAGE_SIZE, &bytes_written); if (bytes_written) hyperv_report_panic_msg(panic_pa, bytes_written);
-- 2.17.1
With the commit message changes,
Reviewed-by: Michael Kelley mikelley@microsoft.com
Thanks for the feedback, Michael. I'll send a v2.
Thanks,
Joe
-----Original Message----- From: Michael Kelley mikelley@microsoft.com Sent: Friday, June 26, 2020 4:53 PM To: Joseph Salisbury Joseph.Salisbury@microsoft.com; KY Srinivasan kys@microsoft.com; Haiyang Zhang haiyangz@microsoft.com; Stephen Hemminger sthemmin@microsoft.com; sashal@kernel.org; wei.liu@kernel.org Cc: linux-hyperv@vger.kernel.org; linux-kernel@vger.kernel.org; stable@vger.kernel.org Subject: RE: [PATCH] Drivers: hv: Change flag to write log level in panic msg to false
From: Joseph Salisbury joseph.salisbury@microsoft.com Sent: Friday, June 26, 2020 10:48 AM
When the kernel panics, one page worth of kmsg data is written to an allocated page. The Hypervisor is notified of the page address trough the MSR. This panic information is collected on the host. Since we are only collecting one page of data, the full panic message may not be collected.
Each line of the panic message is prefixed with the log level of that particular message in the form <N>, where N is the log level. The typical 4 Kbytes contains anywhere from 50 to 100 lines with that log level prefix.
hv_dmsg_dump() makes a call to kmsg_dump_get_buffer(). The second argument in the call is a bool described as: ‘@syslog: include the “<4>” Prefixes’.
With this change, we will not write the log level to the allocated page. This will provide additional room in the allocated page for more informative panic information.
Let me suggest tightening the commit message a bit, with focus on the "what" and "why" rather than the details of the code change. Also use imperative voice per the Linux kernel guidelines:
When the kernel panics, one page of kmsg data may be collected and sent to Hyper-V to aid in diagnosing the failure. The collected kmsg data typically contains 50 to 100 lines, each of which has a log level prefix that isn't very useful from a diagnostic standpoint. So tell kmsg_dump_get_buffer() to not include the log level, enabling more information that *is* useful to fit in the page.
Requesting in stable kernels, since many kernels running in production are stable releases.
Cc: stable@vger.kernel.org Signed-off-by: Joseph Salisbury joseph.salisbury@microsoft.com
drivers/hv/vmbus_drv.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c index 9147ee9d5f7d..d69f4efa3719 100644 --- a/drivers/hv/vmbus_drv.c +++ b/drivers/hv/vmbus_drv.c @@ -1368,7 +1368,7 @@ static void hv_kmsg_dump(struct kmsg_dumper *dumper, * Write dump contents to the page. No need to synchronize; panic should * be single-threaded. */
- kmsg_dump_get_buffer(dumper, true, hv_panic_page, HV_HYP_PAGE_SIZE,
- kmsg_dump_get_buffer(dumper, false, hv_panic_page, HV_HYP_PAGE_SIZE, &bytes_written); if (bytes_written) hyperv_report_panic_msg(panic_pa, bytes_written);
-- 2.17.1
With the commit message changes,
Reviewed-by: Michael Kelley mikelley@microsoft.com
From: Joseph Salisbury Joseph.Salisbury@microsoft.com Sent: Friday, June 26, 2020 3:16 PM
Thanks for the feedback, Michael. I'll send a v2.
Thanks,
Joe
A quick note: The style on the Linux kernel mailing lists is to always reply inline, after the text you are replying to. This is quite different from the style usually used inside Microsoft, which is called "top posting".
Michael
-----Original Message----- From: Michael Kelley mikelley@microsoft.com Sent: Friday, June 26, 2020 4:53 PM To: Joseph Salisbury Joseph.Salisbury@microsoft.com; KY Srinivasan kys@microsoft.com; Haiyang Zhang haiyangz@microsoft.com; Stephen Hemminger sthemmin@microsoft.com; sashal@kernel.org; wei.liu@kernel.org Cc: linux-hyperv@vger.kernel.org; linux-kernel@vger.kernel.org; stable@vger.kernel.org Subject: RE: [PATCH] Drivers: hv: Change flag to write log level in panic msg to false
From: Joseph Salisbury joseph.salisbury@microsoft.com Sent: Friday, June 26, 2020 10:48 AM
When the kernel panics, one page worth of kmsg data is written to an allocated page. The Hypervisor is notified of the page address trough the MSR. This panic information is collected on the host. Since we are only collecting one page of data, the full panic message may not be collected.
Each line of the panic message is prefixed with the log level of that particular message in the form <N>, where N is the log level. The typical 4 Kbytes contains anywhere from 50 to 100 lines with that log level prefix.
hv_dmsg_dump() makes a call to kmsg_dump_get_buffer(). The second argument in the call is a bool described as: ‘@syslog: include the “<4>” Prefixes’.
With this change, we will not write the log level to the allocated page. This will provide additional room in the allocated page for more informative panic information.
Let me suggest tightening the commit message a bit, with focus on the "what" and "why" rather than the details of the code change. Also use imperative voice per the Linux kernel guidelines:
When the kernel panics, one page of kmsg data may be collected and sent to Hyper-V to aid in diagnosing the failure. The collected kmsg data typically contains 50 to 100 lines, each of which has a log level prefix that isn't very useful from a diagnostic standpoint. So tell kmsg_dump_get_buffer() to not include the log level, enabling more information that *is* useful to fit in the page.
Requesting in stable kernels, since many kernels running in production are stable releases.
Cc: stable@vger.kernel.org Signed-off-by: Joseph Salisbury joseph.salisbury@microsoft.com
drivers/hv/vmbus_drv.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c index 9147ee9d5f7d..d69f4efa3719 100644 --- a/drivers/hv/vmbus_drv.c +++ b/drivers/hv/vmbus_drv.c @@ -1368,7 +1368,7 @@ static void hv_kmsg_dump(struct kmsg_dumper *dumper, * Write dump contents to the page. No need to synchronize; panic should * be single-threaded. */
- kmsg_dump_get_buffer(dumper, true, hv_panic_page, HV_HYP_PAGE_SIZE,
- kmsg_dump_get_buffer(dumper, false, hv_panic_page, HV_HYP_PAGE_SIZE, &bytes_written); if (bytes_written) hyperv_report_panic_msg(panic_pa, bytes_written);
-- 2.17.1
With the commit message changes,
Reviewed-by: Michael Kelley mikelley@microsoft.com
-----Original Message----- From: Michael Kelley mikelley@microsoft.com Sent: Friday, June 26, 2020 6:24 PM To: Joseph Salisbury Joseph.Salisbury@microsoft.com; KY Srinivasan kys@microsoft.com; Haiyang Zhang haiyangz@microsoft.com; Stephen Hemminger sthemmin@microsoft.com; sashal@kernel.org; wei.liu@kernel.org Cc: linux-hyperv@vger.kernel.org; linux-kernel@vger.kernel.org; stable@vger.kernel.org Subject: RE: [PATCH] Drivers: hv: Change flag to write log level in panic msg to false
From: Joseph Salisbury Joseph.Salisbury@microsoft.com Sent: Friday, June 26, 2020 3:16 PM
Thanks for the feedback, Michael. I'll send a v2.
Thanks,
Joe
A quick note: The style on the Linux kernel mailing lists is to always reply inline, after the text you are replying to. This is quite different from the style usually used inside Microsoft, which is called "top posting".
Michael
ACK, thanks!
Joe
-----Original Message----- From: Michael Kelley mikelley@microsoft.com Sent: Friday, June 26, 2020 4:53 PM To: Joseph Salisbury Joseph.Salisbury@microsoft.com; KY Srinivasan kys@microsoft.com; Haiyang Zhang haiyangz@microsoft.com; Stephen Hemminger sthemmin@microsoft.com; sashal@kernel.org; wei.liu@kernel.org Cc: linux-hyperv@vger.kernel.org; linux-kernel@vger.kernel.org; stable@vger.kernel.org Subject: RE: [PATCH] Drivers: hv: Change flag to write log level in panic msg to false
From: Joseph Salisbury joseph.salisbury@microsoft.com Sent: Friday, June 26, 2020 10:48 AM
When the kernel panics, one page worth of kmsg data is written to an allocated page. The Hypervisor is notified of the page address trough the MSR. This panic information is collected on the host. Since we are only collecting one page of data, the full panic message may not be collected.
Each line of the panic message is prefixed with the log level of that particular message in the form <N>, where N is the log level. The typical 4 Kbytes contains anywhere from 50 to 100 lines with that log level prefix.
hv_dmsg_dump() makes a call to kmsg_dump_get_buffer(). The second argument in the call is a bool described as: ‘@syslog: include the “<4>” Prefixes’.
With this change, we will not write the log level to the allocated page. This will provide additional room in the allocated page for more informative panic information.
Let me suggest tightening the commit message a bit, with focus on the "what" and "why" rather than the details of the code change. Also use imperative voice per the Linux kernel guidelines:
When the kernel panics, one page of kmsg data may be collected and sent to Hyper-V to aid in diagnosing the failure. The collected kmsg data typically contains 50 to 100 lines, each of which has a log level prefix that isn't very useful from a diagnostic standpoint. So tell kmsg_dump_get_buffer() to not include the log level, enabling more information that *is* useful to fit in the page.
Requesting in stable kernels, since many kernels running in production are stable releases.
Cc: stable@vger.kernel.org Signed-off-by: Joseph Salisbury joseph.salisbury@microsoft.com
drivers/hv/vmbus_drv.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c index 9147ee9d5f7d..d69f4efa3719 100644 --- a/drivers/hv/vmbus_drv.c +++ b/drivers/hv/vmbus_drv.c @@ -1368,7 +1368,7 @@ static void hv_kmsg_dump(struct kmsg_dumper *dumper, * Write dump contents to the page. No need to synchronize; panic should * be single-threaded. */
- kmsg_dump_get_buffer(dumper, true, hv_panic_page, HV_HYP_PAGE_SIZE,
- kmsg_dump_get_buffer(dumper, false, hv_panic_page,
+HV_HYP_PAGE_SIZE, &bytes_written); if (bytes_written) hyperv_report_panic_msg(panic_pa, bytes_written); -- 2.17.1
With the commit message changes,
Reviewed-by: Michael Kelley mikelley@microsoft.com
Hi
[This is an automated email]
This commit has been processed because it contains a -stable tag. The stable tag indicates that it's relevant for the following trees: all
The bot has tested the following trees: v5.7.6, v5.4.49, v4.19.130, v4.14.186, v4.9.228, v4.4.228.
v5.7.6: Build OK! v5.4.49: Failed to apply! Possible dependencies: 53edce00ceb74 ("Drivers: hv: vmbus: Remove dependencies on guest page size")
v4.19.130: Failed to apply! Possible dependencies: 53edce00ceb74 ("Drivers: hv: vmbus: Remove dependencies on guest page size")
v4.14.186: Failed to apply! Possible dependencies: 4a5f3cde4d51c ("Drivers: hv: vmbus: Remove x86-isms from arch independent drivers") 53edce00ceb74 ("Drivers: hv: vmbus: Remove dependencies on guest page size") 7ed4325a44ea5 ("Drivers: hv: vmbus: Make panic reporting to be more useful") 81b18bce48af3 ("Drivers: HV: Send one page worth of kmsg dump over Hyper-V during panic") 8afc06dd75c06 ("Drivers: hv: vmbus: Fix the issue with freeing up hv_ctl_table_hdr") ddcaf3ca4c3c8 ("Drivers: hv: vmus: Fix the check for return value from kmsg get dump buffer")
v4.9.228: Failed to apply! Possible dependencies: 4a5f3cde4d51c ("Drivers: hv: vmbus: Remove x86-isms from arch independent drivers") 6ab42a66d2cc1 ("Drivers: hv: vmbus: Move Hypercall invocation code out of common code") 73638cddaad86 ("Drivers: hv: vmbus: Move the check for hypercall page setup") 76d36ab798204 ("hv: switch to cpuhp state machine for synic init/cleanup") 81b18bce48af3 ("Drivers: HV: Send one page worth of kmsg dump over Hyper-V during panic") 8730046c1498e ("Drivers: hv vmbus: Move Hypercall page setup out of common code") d058fa7e98ff0 ("Drivers: hv: vmbus: Move the crash notification function")
v4.4.228: Failed to apply! Possible dependencies: 4a5f3cde4d51c ("Drivers: hv: vmbus: Remove x86-isms from arch independent drivers") 619848bd07434 ("drivers:hv: Export a function that maps Linux CPU num onto Hyper-V proc num") 6ab42a66d2cc1 ("Drivers: hv: vmbus: Move Hypercall invocation code out of common code") 73638cddaad86 ("Drivers: hv: vmbus: Move the check for hypercall page setup") 75ff3a8a9168d ("Drivers: hv: vmbus: avoid wait_for_completion() on crash") 76d36ab798204 ("hv: switch to cpuhp state machine for synic init/cleanup") 81b18bce48af3 ("Drivers: HV: Send one page worth of kmsg dump over Hyper-V during panic") 8730046c1498e ("Drivers: hv vmbus: Move Hypercall page setup out of common code") a108393dbf764 ("drivers:hv: Export the API to invoke a hypercall on Hyper-V") d058fa7e98ff0 ("Drivers: hv: vmbus: Move the crash notification function")
NOTE: The patch will not be queued to stable trees until it is upstream.
How should we proceed with this patch?
linux-stable-mirror@lists.linaro.org
-
Joseph Salisbury -
Joseph Salisbury
-
Michael Kelley -
Sasha Levin