FAILED: Patch "posix-cpu-timers: Clear TICK_DEP_BIT_POSIX_TIMER on clone" failed to apply to v4.19-stable tree

Posted by Sasha Levin 2 weeks, 4 days ago

The patch below does not apply to the v4.19-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@vger.kernel.org>.

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From b5413156bad91dc2995a5c4eab1b05e56914638a Mon Sep 17 00:00:00 2001
From: Benjamin Segall <bsegall@google.com>
Date: Fri, 25 Oct 2024 18:35:35 -0700
Subject: [PATCH] posix-cpu-timers: Clear TICK_DEP_BIT_POSIX_TIMER on clone

When cloning a new thread, its posix_cputimers are not inherited, and
are cleared by posix_cputimers_init(). However, this does not clear the
tick dependency it creates in tsk->tick_dep_mask, and the handler does
not reach the code to clear the dependency if there were no timers to
begin with.

Thus if a thread has a cputimer running before clone/fork, all
descendants will prevent nohz_full unless they create a cputimer of
their own.

Fix this by entirely clearing the tick_dep_mask in copy_process().
(There is currently no inherited state that needs a tick dependency)

Process-wide timers do not have this problem because fork does not copy
signal_struct as a baseline, it creates one from scratch.

Fixes: b78783000d5c ("posix-cpu-timers: Migrate to use new tick dependency mask model")
Signed-off-by: Ben Segall <bsegall@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/all/xm26o737bq8o.fsf@google.com
---
 include/linux/tick.h | 8 ++++++++
 kernel/fork.c        | 2 ++
 2 files changed, 10 insertions(+)

diff --git a/include/linux/tick.h b/include/linux/tick.h
index 72744638c5b0f..99c9c5a7252aa 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -251,12 +251,19 @@ static inline void tick_dep_set_task(struct task_struct *tsk,
 	if (tick_nohz_full_enabled())
 		tick_nohz_dep_set_task(tsk, bit);
 }
+
 static inline void tick_dep_clear_task(struct task_struct *tsk,
 				       enum tick_dep_bits bit)
 {
 	if (tick_nohz_full_enabled())
 		tick_nohz_dep_clear_task(tsk, bit);
 }
+
+static inline void tick_dep_init_task(struct task_struct *tsk)
+{
+	atomic_set(&tsk->tick_dep_mask, 0);
+}
+
 static inline void tick_dep_set_signal(struct task_struct *tsk,
 				       enum tick_dep_bits bit)
 {
@@ -290,6 +297,7 @@ static inline void tick_dep_set_task(struct task_struct *tsk,
 				     enum tick_dep_bits bit) { }
 static inline void tick_dep_clear_task(struct task_struct *tsk,
 				       enum tick_dep_bits bit) { }
+static inline void tick_dep_init_task(struct task_struct *tsk) { }
 static inline void tick_dep_set_signal(struct task_struct *tsk,
 				       enum tick_dep_bits bit) { }
 static inline void tick_dep_clear_signal(struct signal_struct *signal,
diff --git a/kernel/fork.c b/kernel/fork.c
index 89ceb4a68af25..6fa9fe62e01e3 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -105,6 +105,7 @@
 #include <linux/rseq.h>
 #include <uapi/linux/pidfd.h>
 #include <linux/pidfs.h>
+#include <linux/tick.h>
 
 #include <asm/pgalloc.h>
 #include <linux/uaccess.h>
@@ -2292,6 +2293,7 @@ __latent_entropy struct task_struct *copy_process(
 	acct_clear_integrals(p);
 
 	posix_cputimers_init(&p->posix_cputimers);
+	tick_dep_init_task(p);
 
 	p->io_context = NULL;
 	audit_set_context(p, NULL);
-- 
2.43.0

Re: FAILED: Patch "posix-cpu-timers: Clear TICK_DEP_BIT_POSIX_TIMER on clone" failed to apply to v4.19-stable tree

Posted by Frederic Weisbecker 2 weeks, 2 days ago

Le Tue, Nov 05, 2024 at 09:14:15PM -0500, Sasha Levin a écrit :
> The patch below does not apply to the v4.19-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@vger.kernel.org>.
> 
> Thanks,
> Sasha

Please try this:

---
From ee0d95090203b7ee4cb1f29c586cd7d0dbf79fff Mon Sep 17 00:00:00 2001
From: Benjamin Segall <bsegall@google.com>
Date: Fri, 25 Oct 2024 18:35:35 -0700
Subject: [PATCH] posix-cpu-timers: Clear TICK_DEP_BIT_POSIX_TIMER on clone

When cloning a new thread, its posix_cputimers are not inherited, and
are cleared by posix_cputimers_init(). However, this does not clear the
tick dependency it creates in tsk->tick_dep_mask, and the handler does
not reach the code to clear the dependency if there were no timers to
begin with.

Thus if a thread has a cputimer running before clone/fork, all
descendants will prevent nohz_full unless they create a cputimer of
their own.

Fix this by entirely clearing the tick_dep_mask in copy_process().
(There is currently no inherited state that needs a tick dependency)

Process-wide timers do not have this problem because fork does not copy
signal_struct as a baseline, it creates one from scratch.

Fixes: b78783000d5c ("posix-cpu-timers: Migrate to use new tick dependency mask model")
Signed-off-by: Ben Segall <bsegall@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/all/xm26o737bq8o.fsf@google.com
---
 include/linux/tick.h | 8 ++++++++
 kernel/fork.c        | 2 ++
 2 files changed, 10 insertions(+)

diff --git a/include/linux/tick.h b/include/linux/tick.h
index 443726085f6c..832381b812c2 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -233,12 +233,19 @@ static inline void tick_dep_set_task(struct task_struct *tsk,
 	if (tick_nohz_full_enabled())
 		tick_nohz_dep_set_task(tsk, bit);
 }
+
 static inline void tick_dep_clear_task(struct task_struct *tsk,
 				       enum tick_dep_bits bit)
 {
 	if (tick_nohz_full_enabled())
 		tick_nohz_dep_clear_task(tsk, bit);
 }
+
+static inline void tick_dep_init_task(struct task_struct *tsk)
+{
+	atomic_set(&tsk->tick_dep_mask, 0);
+}
+
 static inline void tick_dep_set_signal(struct signal_struct *signal,
 				       enum tick_dep_bits bit)
 {
@@ -272,6 +279,7 @@ static inline void tick_dep_set_task(struct task_struct *tsk,
 				     enum tick_dep_bits bit) { }
 static inline void tick_dep_clear_task(struct task_struct *tsk,
 				       enum tick_dep_bits bit) { }
+static inline void tick_dep_init_task(struct task_struct *tsk) { }
 static inline void tick_dep_set_signal(struct signal_struct *signal,
 				       enum tick_dep_bits bit) { }
 static inline void tick_dep_clear_signal(struct signal_struct *signal,
diff --git a/kernel/fork.c b/kernel/fork.c
index b65871600507..1fb06d8952bc 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -91,6 +91,7 @@
 #include <linux/kcov.h>
 #include <linux/livepatch.h>
 #include <linux/thread_info.h>
+#include <linux/tick.h>
 
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>
@@ -1829,6 +1830,7 @@ static __latent_entropy struct task_struct *copy_process(
 	acct_clear_integrals(p);
 
 	posix_cpu_timers_init(p);
+	tick_dep_init_task(p);
 
 	p->io_context = NULL;
 	audit_set_context(p, NULL);
-- 
2.46.0

Re: FAILED: Patch "posix-cpu-timers: Clear TICK_DEP_BIT_POSIX_TIMER on clone" failed to apply to v4.19-stable tree

Posted by Greg KH 2 weeks ago

On Thu, Nov 07, 2024 at 11:23:24AM +0100, Frederic Weisbecker wrote:
> Le Tue, Nov 05, 2024 at 09:14:15PM -0500, Sasha Levin a écrit :
> > The patch below does not apply to the v4.19-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@vger.kernel.org>.
> > 
> > Thanks,
> > Sasha
> 
> Please try this:
> 
> ---
> >From ee0d95090203b7ee4cb1f29c586cd7d0dbf79fff Mon Sep 17 00:00:00 2001
> From: Benjamin Segall <bsegall@google.com>
> Date: Fri, 25 Oct 2024 18:35:35 -0700
> Subject: [PATCH] posix-cpu-timers: Clear TICK_DEP_BIT_POSIX_TIMER on clone
> 
> When cloning a new thread, its posix_cputimers are not inherited, and
> are cleared by posix_cputimers_init(). However, this does not clear the
> tick dependency it creates in tsk->tick_dep_mask, and the handler does
> not reach the code to clear the dependency if there were no timers to
> begin with.
> 
> Thus if a thread has a cputimer running before clone/fork, all
> descendants will prevent nohz_full unless they create a cputimer of
> their own.
> 
> Fix this by entirely clearing the tick_dep_mask in copy_process().
> (There is currently no inherited state that needs a tick dependency)
> 
> Process-wide timers do not have this problem because fork does not copy
> signal_struct as a baseline, it creates one from scratch.
> 
> Fixes: b78783000d5c ("posix-cpu-timers: Migrate to use new tick dependency mask model")
> Signed-off-by: Ben Segall <bsegall@google.com>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
> Cc: stable@vger.kernel.org
> Link: https://lore.kernel.org/all/xm26o737bq8o.fsf@google.com
> ---
>  include/linux/tick.h | 8 ++++++++
>  kernel/fork.c        | 2 ++
>  2 files changed, 10 insertions(+)
> 
> diff --git a/include/linux/tick.h b/include/linux/tick.h
> index 443726085f6c..832381b812c2 100644
> --- a/include/linux/tick.h
> +++ b/include/linux/tick.h
> @@ -233,12 +233,19 @@ static inline void tick_dep_set_task(struct task_struct *tsk,
>  	if (tick_nohz_full_enabled())
>  		tick_nohz_dep_set_task(tsk, bit);
>  }
> +
>  static inline void tick_dep_clear_task(struct task_struct *tsk,
>  				       enum tick_dep_bits bit)
>  {
>  	if (tick_nohz_full_enabled())
>  		tick_nohz_dep_clear_task(tsk, bit);
>  }
> +
> +static inline void tick_dep_init_task(struct task_struct *tsk)
> +{
> +	atomic_set(&tsk->tick_dep_mask, 0);
> +}
> +
>  static inline void tick_dep_set_signal(struct signal_struct *signal,
>  				       enum tick_dep_bits bit)
>  {
> @@ -272,6 +279,7 @@ static inline void tick_dep_set_task(struct task_struct *tsk,
>  				     enum tick_dep_bits bit) { }
>  static inline void tick_dep_clear_task(struct task_struct *tsk,
>  				       enum tick_dep_bits bit) { }
> +static inline void tick_dep_init_task(struct task_struct *tsk) { }
>  static inline void tick_dep_set_signal(struct signal_struct *signal,
>  				       enum tick_dep_bits bit) { }
>  static inline void tick_dep_clear_signal(struct signal_struct *signal,
> diff --git a/kernel/fork.c b/kernel/fork.c
> index b65871600507..1fb06d8952bc 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -91,6 +91,7 @@
>  #include <linux/kcov.h>
>  #include <linux/livepatch.h>
>  #include <linux/thread_info.h>
> +#include <linux/tick.h>
>  
>  #include <asm/pgtable.h>
>  #include <asm/pgalloc.h>
> @@ -1829,6 +1830,7 @@ static __latent_entropy struct task_struct *copy_process(
>  	acct_clear_integrals(p);
>  
>  	posix_cpu_timers_init(p);
> +	tick_dep_init_task(p);
>  
>  	p->io_context = NULL;
>  	audit_set_context(p, NULL);
> -- 
> 2.46.0
> 
> 

What is the git id of this in Linus's tree?

thanks,

greg k-h

Re: FAILED: Patch "posix-cpu-timers: Clear TICK_DEP_BIT_POSIX_TIMER on clone" failed to apply to v4.19-stable tree

Posted by Frederic Weisbecker 1 week, 5 days ago

Hi Greg,

Le Sat, Nov 09, 2024 at 03:54:09PM +0100, Greg KH a écrit :
> On Thu, Nov 07, 2024 at 11:23:24AM +0100, Frederic Weisbecker wrote:
> > Le Tue, Nov 05, 2024 at 09:14:15PM -0500, Sasha Levin a écrit :
> > > The patch below does not apply to the v4.19-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@vger.kernel.org>.
> > > 
> > > Thanks,
> > > Sasha
> > 
> > Please try this:
> > 
> > ---
> > >From ee0d95090203b7ee4cb1f29c586cd7d0dbf79fff Mon Sep 17 00:00:00 2001
> > From: Benjamin Segall <bsegall@google.com>
> > Date: Fri, 25 Oct 2024 18:35:35 -0700
> > Subject: [PATCH] posix-cpu-timers: Clear TICK_DEP_BIT_POSIX_TIMER on clone
> > 
> > When cloning a new thread, its posix_cputimers are not inherited, and
> > are cleared by posix_cputimers_init(). However, this does not clear the
> > tick dependency it creates in tsk->tick_dep_mask, and the handler does
> > not reach the code to clear the dependency if there were no timers to
> > begin with.
> > 
> > Thus if a thread has a cputimer running before clone/fork, all
> > descendants will prevent nohz_full unless they create a cputimer of
> > their own.
> > 
> > Fix this by entirely clearing the tick_dep_mask in copy_process().
> > (There is currently no inherited state that needs a tick dependency)
> > 
> > Process-wide timers do not have this problem because fork does not copy
> > signal_struct as a baseline, it creates one from scratch.
> > 
> > Fixes: b78783000d5c ("posix-cpu-timers: Migrate to use new tick dependency mask model")
> > Signed-off-by: Ben Segall <bsegall@google.com>
> > Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> > Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
> > Cc: stable@vger.kernel.org
> > Link: https://lore.kernel.org/all/xm26o737bq8o.fsf@google.com
> > ---
> >  include/linux/tick.h | 8 ++++++++
> >  kernel/fork.c        | 2 ++
> >  2 files changed, 10 insertions(+)
> > 
> > diff --git a/include/linux/tick.h b/include/linux/tick.h
> > index 443726085f6c..832381b812c2 100644
> > --- a/include/linux/tick.h
> > +++ b/include/linux/tick.h
> > @@ -233,12 +233,19 @@ static inline void tick_dep_set_task(struct task_struct *tsk,
> >  	if (tick_nohz_full_enabled())
> >  		tick_nohz_dep_set_task(tsk, bit);
> >  }
> > +
> >  static inline void tick_dep_clear_task(struct task_struct *tsk,
> >  				       enum tick_dep_bits bit)
> >  {
> >  	if (tick_nohz_full_enabled())
> >  		tick_nohz_dep_clear_task(tsk, bit);
> >  }
> > +
> > +static inline void tick_dep_init_task(struct task_struct *tsk)
> > +{
> > +	atomic_set(&tsk->tick_dep_mask, 0);
> > +}
> > +
> >  static inline void tick_dep_set_signal(struct signal_struct *signal,
> >  				       enum tick_dep_bits bit)
> >  {
> > @@ -272,6 +279,7 @@ static inline void tick_dep_set_task(struct task_struct *tsk,
> >  				     enum tick_dep_bits bit) { }
> >  static inline void tick_dep_clear_task(struct task_struct *tsk,
> >  				       enum tick_dep_bits bit) { }
> > +static inline void tick_dep_init_task(struct task_struct *tsk) { }
> >  static inline void tick_dep_set_signal(struct signal_struct *signal,
> >  				       enum tick_dep_bits bit) { }
> >  static inline void tick_dep_clear_signal(struct signal_struct *signal,
> > diff --git a/kernel/fork.c b/kernel/fork.c
> > index b65871600507..1fb06d8952bc 100644
> > --- a/kernel/fork.c
> > +++ b/kernel/fork.c
> > @@ -91,6 +91,7 @@
> >  #include <linux/kcov.h>
> >  #include <linux/livepatch.h>
> >  #include <linux/thread_info.h>
> > +#include <linux/tick.h>
> >  
> >  #include <asm/pgtable.h>
> >  #include <asm/pgalloc.h>
> > @@ -1829,6 +1830,7 @@ static __latent_entropy struct task_struct *copy_process(
> >  	acct_clear_integrals(p);
> >  
> >  	posix_cpu_timers_init(p);
> > +	tick_dep_init_task(p);
> >  
> >  	p->io_context = NULL;
> >  	audit_set_context(p, NULL);
> > -- 
> > 2.46.0
> > 
> > 
> 
> What is the git id of this in Linus's tree?

b5413156bad9 (posix-cpu-timers: Clear TICK_DEP_BIT_POSIX_TIMER on clone)

Thanks.

> 
> thanks,
> 
> greg k-h