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posix-cpu-timers: Clear TICK_DEP_BIT_POSIX_TIMER on clone

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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: b78783000d ("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
This commit is contained in:
Benjamin Segall 2024-10-25 18:35:35 -07:00 committed by Thomas Gleixner
parent 42f7652d3e
commit b5413156ba
2 changed files with 10 additions and 0 deletions
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8
include/linux/tick.h
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@ -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,

2
kernel/fork.c
View File

@ -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);