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