The following commit has been merged into the timers/urgent branch of tip:

Commit-ID: b5413156bad91dc2995a5c4eab1b05e56914638a Gitweb: https://git.kernel.org/tip/b5413156bad91dc2995a5c4eab1b05e56914638a Author: Benjamin Segall bsegall@google.com AuthorDate: Fri, 25 Oct 2024 18:35:35 -07:00 Committer: Thomas Gleixner tglx@linutronix.de CommitterDate: Sun, 27 Oct 2024 10:36:04 +01:00

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 7274463..99c9c5a 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 89ceb4a..6fa9fe6 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);