5.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Benjamin Segall bsegall@google.com
[ Upstream commit b5413156bad91dc2995a5c4eab1b05e56914638a ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- 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 9459fef5b8573..9701c571a5cfe 100644 --- a/include/linux/tick.h +++ b/include/linux/tick.h @@ -252,12 +252,19 @@ 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) { @@ -291,6 +298,7 @@ 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 fec103ae640ff..23ffcf8a859c5 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -97,6 +97,7 @@ #include <linux/scs.h> #include <linux/io_uring.h> #include <linux/bpf.h> +#include <linux/tick.h>
#include <asm/pgalloc.h> #include <linux/uaccess.h> @@ -2126,6 +2127,7 @@ static __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);