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

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Message-ID: <2024110957-anaconda-papaya-2f0a@gregkh>
Date: Sat, 9 Nov 2024 15:54:09 +0100
From: Greg KH <gregkh@...uxfoundation.org>
To: Frederic Weisbecker <frederic@...nel.org>
Cc: Sasha Levin <sashal@...nel.org>, stable@...r.kernel.org,
	bsegall@...gle.com, Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: FAILED: Patch "posix-cpu-timers: Clear TICK_DEP_BIT_POSIX_TIMER
 on clone" failed to apply to v4.19-stable tree

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@...r.kernel.org>.
> > 
> > Thanks,
> > Sasha
> 
> Please try this:
> 
> ---
> >From ee0d95090203b7ee4cb1f29c586cd7d0dbf79fff Mon Sep 17 00:00:00 2001
> From: Benjamin Segall <bsegall@...gle.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@...gle.com>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Reviewed-by: Frederic Weisbecker <frederic@...nel.org>
> Cc: stable@...r.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