Re: [Cocci] [PATCH V2] kernel/hung_task.c: Introduce sysctl to print all traces when a hung task is detected
On 3/24/20 7:20 PM, Kees Cook wrote: > On Tue, Mar 24, 2020 at 09:45:40AM -0300, Guilherme G. Piccoli wrote: >> Thanks Randy and Vlastimil for the comments. I really liked your >> approach Vlastimil, I agree that we have no reason to not have a generic >> sysctl setting via cmdline mechanism - I'll rework this patch removing >> the kernel parameter (same for other patch I just submitted). > > I've been thinking we'll likely want to have a big patch series that > removes all the old "duplicate" boot params and adds some kind of > "alias" mechanism. > > Vlastimil, have you happened to keep a list of other "redundant" boot > params you've noticed in the kernel? I bet there are a lot. :) Well, I found about 4 that mentioned sysctl in Documentation/admin-guide/kernel-parameters.txt I suspect there will be more, but won't be trivial to identify them. ___ Cocci mailing list Cocci@systeme.lip6.fr https://systeme.lip6.fr/mailman/listinfo/cocci
Re: [Cocci] [PATCH V2] kernel/hung_task.c: Introduce sysctl to print all traces when a hung task is detected
On Tue, Mar 24, 2020 at 09:45:40AM -0300, Guilherme G. Piccoli wrote: > Thanks Randy and Vlastimil for the comments. I really liked your > approach Vlastimil, I agree that we have no reason to not have a generic > sysctl setting via cmdline mechanism - I'll rework this patch removing > the kernel parameter (same for other patch I just submitted). I've been thinking we'll likely want to have a big patch series that removes all the old "duplicate" boot params and adds some kind of "alias" mechanism. Vlastimil, have you happened to keep a list of other "redundant" boot params you've noticed in the kernel? I bet there are a lot. :) -- Kees Cook ___ Cocci mailing list Cocci@systeme.lip6.fr https://systeme.lip6.fr/mailman/listinfo/cocci
Re: [Cocci] [PATCH V2] kernel/hung_task.c: Introduce sysctl to print all traces when a hung task is detected
On 3/23/20 10:46 PM, Guilherme G. Piccoli wrote:
> Commit 401c636a0eeb ("kernel/hung_task.c: show all hung tasks before panic")
> introduced a change in that we started to show all CPUs backtraces when a
> hung task is detected _and_ the sysctl/kernel parameter "hung_task_panic"
> is set. The idea is good, because usually when observing deadlocks (that
> may lead to hung tasks), the culprit is another task holding a lock and
> not necessarily the task detected as hung.
>
> The problem with this approach is that dumping backtraces is a slightly
> expensive task, specially printing that on console (and specially in many
> CPU machines, as servers commonly found nowadays). So, users that plan to
> collect a kdump to investigate the hung tasks and narrow down the deadlock
> definitely don't need the CPUs backtrace on dmesg/console, which will delay
> the panic and pollute the log (crash tool would easily grab all CPUs traces
> with 'bt -a' command).
> Also, there's the reciprocal scenario: some users may be interested in
> seeing the CPUs backtraces but not have the system panic when a hung task
> is detected. The current approach hence is almost as embedding a policy in
> the kernel, by forcing the CPUs backtraces' dump (only) on hung_task_panic.
>
> This patch decouples the panic event on hung task from the CPUs backtraces
> dump, by creating (and documenting) a new sysctl/kernel parameter called
> "hung_task_all_cpu_backtrace", analog to the approach taken on soft/hard
> lockups, that have both a panic and an "all_cpu_backtrace" sysctl to allow
> individual control. The new mechanism for dumping the CPUs backtraces on
> hung task detection respects "hung_task_warnings" by not dumping the
> traces in case there's no warnings left.
>
> Cc: Tetsuo Handa
> Signed-off-by: Guilherme G. Piccoli
> ---
>
>
> V2: Followed suggestions from Kees and Tetsuo (and other grammar
> improvements). Also, followed Tetsuo suggestion to itereate kernel
> testing community - but I don't really know a ML for that, so I've
> CCed Coccinelle community and kernel-api ML.
>
> Also, Tetsuo suggested that this option could be default to 1 - I'm
> open to it, but given it is only available if hung_task panic is set
> as of now and the goal of this patch is give users more flexibility,
> I vote to keep default as 0. I can respin a V3 in case more people
> want to see it enabled by default. Thanks in advance for the review!
> Cheers,
>
> Guilherme
>
>
> .../admin-guide/kernel-parameters.txt | 6
> Documentation/admin-guide/sysctl/kernel.rst | 15 ++
> include/linux/sched/sysctl.h | 7 +
> kernel/hung_task.c| 30 +--
> kernel/sysctl.c | 11 +++
> 5 files changed, 67 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt
> b/Documentation/admin-guide/kernel-parameters.txt
> index c07815d230bc..7a14caac6c94 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1453,6 +1453,12 @@
> x86-64 are 2M (when the CPU supports "pse") and 1G
> (when the CPU supports the "pdpe1gb" cpuinfo flag).
>
> + hung_task_all_cpu_backtrace=
> + [KNL] Should kernel generate backtraces on all cpus
> + when a hung task is detected. Defaults to 0 and can
> + be controlled by hung_task_all_cpu_backtrace sysctl.
> + Format:
> +
Before adding a new thing as both kernel parameter and sysctl, could we perhaps
not add the kernel parameter, in favor of the generic sysctl parameter solution?
[1] There were no objections and some support from Kees, so I will try to send a
new version ASAP that will work properly with all "static" sysctls - we don't
need to be blocked by a full solution for dynamically registered sysctls yet, I
guess?
Thanks,
Vlastimil
[1] https://lore.kernel.org/linux-api/20200317132105.24555-1-vba...@suse.cz/
___
Cocci mailing list
Cocci@systeme.lip6.fr
https://systeme.lip6.fr/mailman/listinfo/cocci
Re: [Cocci] [PATCH V2] kernel/hung_task.c: Introduce sysctl to print all traces when a hung task is detected
Hi, On 3/23/20 2:46 PM, Guilherme G. Piccoli wrote: > > .../admin-guide/kernel-parameters.txt | 6 > Documentation/admin-guide/sysctl/kernel.rst | 15 ++ > include/linux/sched/sysctl.h | 7 + > kernel/hung_task.c| 30 +-- > kernel/sysctl.c | 11 +++ > 5 files changed, 67 insertions(+), 2 deletions(-) > admin-guide/kernel-parameters.txt predominantly uses "CPUs" for plural CPUs when not part of a cmdline keyword etc., so please adjust below: > diff --git a/Documentation/admin-guide/kernel-parameters.txt > b/Documentation/admin-guide/kernel-parameters.txt > index c07815d230bc..7a14caac6c94 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -1453,6 +1453,12 @@ > x86-64 are 2M (when the CPU supports "pse") and 1G > (when the CPU supports the "pdpe1gb" cpuinfo flag). > > + hung_task_all_cpu_backtrace= > + [KNL] Should kernel generate backtraces on all cpus CPUs > + when a hung task is detected. Defaults to 0 and can > + be controlled by hung_task_all_cpu_backtrace sysctl. > + Format: > + > hung_task_panic= > [KNL] Should the hung task detector generate panics. > Format: > diff --git a/Documentation/admin-guide/sysctl/kernel.rst > b/Documentation/admin-guide/sysctl/kernel.rst > index def074807cee..8b4ff69d2348 100644 > --- a/Documentation/admin-guide/sysctl/kernel.rst > +++ b/Documentation/admin-guide/sysctl/kernel.rst > @@ -40,6 +40,7 @@ show up in /proc/sys/kernel: > - hotplug > - hardlockup_all_cpu_backtrace > - hardlockup_panic > +- hung_task_all_cpu_backtrace > - hung_task_panic > - hung_task_check_count > - hung_task_timeout_secs > @@ -338,6 +339,20 @@ Path for the hotplug policy agent. > Default value is "/sbin/hotplug". > > > +hung_task_all_cpu_backtrace: > + > + > +If this option is set, the kernel will send an NMI to all CPUs to dump > +their backtraces when a hung task is detected. This file shows up if > +CONFIG_DETECT_HUNG_TASK and CONFIG_SMP are enabled. > + > +0: Won't show all CPUs backtraces when a hung task is detected. > +This is the default behavior. > + > +1: Will non-maskably interrupt all CPUs and dump their backtraces when > +a hung task is detected. > + > + > hung_task_panic: > > thanks. -- ~Randy ___ Cocci mailing list Cocci@systeme.lip6.fr https://systeme.lip6.fr/mailman/listinfo/cocci
Re: [Cocci] [PATCH V2] kernel/hung_task.c: Introduce sysctl to print all traces when a hung task is detected
On 24/03/2020 05:27, Vlastimil Babka wrote: > [...] > Before adding a new thing as both kernel parameter and sysctl, could we > perhaps > not add the kernel parameter, in favor of the generic sysctl parameter > solution? > [1] There were no objections and some support from Kees, so I will try to > send a > new version ASAP that will work properly with all "static" sysctls - we don't > need to be blocked by a full solution for dynamically registered sysctls yet, > I > guess? > > Thanks, > Vlastimil > > [1] https://lore.kernel.org/linux-api/20200317132105.24555-1-vba...@suse.cz/ > Thanks Randy and Vlastimil for the comments. I really liked your approach Vlastimil, I agree that we have no reason to not have a generic sysctl setting via cmdline mechanism - I'll rework this patch removing the kernel parameter (same for other patch I just submitted). If you can CC me on the new iterations of the generic sysctl patches Vlastimil, I appreciate - I can maybe test that, I'd like to see it in kernel. Thanks, Guilherme ___ Cocci mailing list Cocci@systeme.lip6.fr https://systeme.lip6.fr/mailman/listinfo/cocci
Re: [Cocci] [PATCH V2] kernel/hung_task.c: Introduce sysctl to print all traces when a hung task is detected
On Mon, Mar 23, 2020 at 06:46:18PM -0300, Guilherme G. Piccoli wrote:
> Commit 401c636a0eeb ("kernel/hung_task.c: show all hung tasks before panic")
> introduced a change in that we started to show all CPUs backtraces when a
> hung task is detected _and_ the sysctl/kernel parameter "hung_task_panic"
> is set. The idea is good, because usually when observing deadlocks (that
> may lead to hung tasks), the culprit is another task holding a lock and
> not necessarily the task detected as hung.
>
> The problem with this approach is that dumping backtraces is a slightly
> expensive task, specially printing that on console (and specially in many
> CPU machines, as servers commonly found nowadays). So, users that plan to
> collect a kdump to investigate the hung tasks and narrow down the deadlock
> definitely don't need the CPUs backtrace on dmesg/console, which will delay
> the panic and pollute the log (crash tool would easily grab all CPUs traces
> with 'bt -a' command).
> Also, there's the reciprocal scenario: some users may be interested in
> seeing the CPUs backtraces but not have the system panic when a hung task
> is detected. The current approach hence is almost as embedding a policy in
> the kernel, by forcing the CPUs backtraces' dump (only) on hung_task_panic.
>
> This patch decouples the panic event on hung task from the CPUs backtraces
> dump, by creating (and documenting) a new sysctl/kernel parameter called
> "hung_task_all_cpu_backtrace", analog to the approach taken on soft/hard
> lockups, that have both a panic and an "all_cpu_backtrace" sysctl to allow
> individual control. The new mechanism for dumping the CPUs backtraces on
> hung task detection respects "hung_task_warnings" by not dumping the
> traces in case there's no warnings left.
>
> Cc: Tetsuo Handa
> Signed-off-by: Guilherme G. Piccoli
> ---
>
>
> V2: Followed suggestions from Kees and Tetsuo (and other grammar
> improvements). Also, followed Tetsuo suggestion to itereate kernel
> testing community - but I don't really know a ML for that, so I've
> CCed Coccinelle community and kernel-api ML.
>
> Also, Tetsuo suggested that this option could be default to 1 - I'm
> open to it, but given it is only available if hung_task panic is set
> as of now and the goal of this patch is give users more flexibility,
> I vote to keep default as 0. I can respin a V3 in case more people
> want to see it enabled by default. Thanks in advance for the review!
Yeah, most things like this we've tried to be conservative. I'd like to
see it stay zero too.
Reviewed-by: Kees Cook
-Kees
> Cheers,
>
> Guilherme
>
>
> .../admin-guide/kernel-parameters.txt | 6
> Documentation/admin-guide/sysctl/kernel.rst | 15 ++
> include/linux/sched/sysctl.h | 7 +
> kernel/hung_task.c| 30 +--
> kernel/sysctl.c | 11 +++
> 5 files changed, 67 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt
> b/Documentation/admin-guide/kernel-parameters.txt
> index c07815d230bc..7a14caac6c94 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1453,6 +1453,12 @@
> x86-64 are 2M (when the CPU supports "pse") and 1G
> (when the CPU supports the "pdpe1gb" cpuinfo flag).
>
> + hung_task_all_cpu_backtrace=
> + [KNL] Should kernel generate backtraces on all cpus
> + when a hung task is detected. Defaults to 0 and can
> + be controlled by hung_task_all_cpu_backtrace sysctl.
> + Format:
> +
> hung_task_panic=
> [KNL] Should the hung task detector generate panics.
> Format:
> diff --git a/Documentation/admin-guide/sysctl/kernel.rst
> b/Documentation/admin-guide/sysctl/kernel.rst
> index def074807cee..8b4ff69d2348 100644
> --- a/Documentation/admin-guide/sysctl/kernel.rst
> +++ b/Documentation/admin-guide/sysctl/kernel.rst
> @@ -40,6 +40,7 @@ show up in /proc/sys/kernel:
> - hotplug
> - hardlockup_all_cpu_backtrace
> - hardlockup_panic
> +- hung_task_all_cpu_backtrace
> - hung_task_panic
> - hung_task_check_count
> - hung_task_timeout_secs
> @@ -338,6 +339,20 @@ Path for the hotplug policy agent.
> Default value is "/sbin/hotplug".
>
>
> +hung_task_all_cpu_backtrace:
> +
> +
> +If this option is set, the kernel will send an NMI to all CPUs to dump
> +their backtraces when a hung task is detected. This file shows up if
> +CONFIG_DETECT_HUNG_TASK and CONFIG_SMP are enabled.
> +
> +0: Won't show all CPUs backtraces when a hung task is detected.
> +This is the default behavior.
> +
> +1: Will non-maskably interrupt all CPUs and dump their backtraces when
> +a hung task is detected.
> +
> +
> hung_task_panic:
>
>
> diff
