posix-cpu-timers: clear TICK_DEP_BIT_POSIX_TIMER on clone
Subsystems (5)
Benjamin Segall
reviewerPATCH v3 1/1 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.
--- include/linux/tick.h | 8 ++++++++ kernel/fork.c | 2 ++ 2 files changed, 10 insertions(+)
include/linux/tick.h +8 -0
@@ -249,16 +249,23 @@ static inline void tick_dep_set_task(struct task_struct *tsk, enum tick_dep_bits bit) {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) {if (tick_nohz_full_enabled ())tick_nohz_dep_set_signal (tsk, bit);
@@ -288,10 +295,11 @@ static inline void tick_dep_set_cpu(int cpu, enum tick_dep_bits bit) { }static inline void tick_dep_clear_cpu (int cpu,enum tick_dep_bits bit) { }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,enum tick_dep_bits bit) { }
kernel/fork.c +2 -0
@@ -103,10 +103,11 @@#include <linux/user_events.h> #include <linux/iommu.h> #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> #include <asm/mmu_context.h> #include <asm/cacheflush.h>
@@ -2290,10 +2291,11 @@ __latent_entropy struct task_struct *copy_process(task_io_accounting_init (&p->ioac);acct_clear_integrals (p);posix_cputimers_init (&p->posix_cputimers); +tick_dep_init_task (p); p->io_context =NULL ;audit_set_context (p,NULL );cgroup_fork (p);if (args->kthread) {
Signature · 1 line
2.47.0.163.g1226f6d8fa-goog
Quoted 13 lines · Benjamin Segall
When cloning a new thread, its
posix_cputimersare not inherited, and are cleared byposix_cputimers_init(). However, this does not clear the tick dependency it creates intsk->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_fullunless they create a cputimer of their own.Fix this by entirely clearing the
tick_dep_maskincopy_process(). (There is currently no inherited state that needs a tick dependency)
Quoted 6 lines
Process-wide timers do not have this problem because fork does not copy
signal_structas 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 <[email protected]>
Thanks!
[tip: timers/urgent] posix-cpu-timers: Clear TICK_DEP_BIT_POSIX_TIMER on clone
In reply to Benjamin SegallThe following commit has been merged into the timers/urgent branch of tip:
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 <[email protected]> AuthorDate: Fri, 25 Oct 2024 18:35:35 -07:00 Committer: Thomas Gleixner <[email protected]> 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.
--- include/linux/tick.h | 8 ++++++++ kernel/fork.c | 2 ++ 2 files changed, 10 insertions(+)
include/linux/tick.h +8 -0
@@ -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,
kernel/fork.c +2 -0
@@ -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 );