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exit: combine work under lock in synchronize_group_exit() and coredump_task_exit()

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This reduces single-threaded overhead as it avoids one lock+irq trip on
exit.

It also improves scalability of spawning and killing threads within one
process (just shy of 5% when doing it on 24 cores on my test jig).

Both routines are moved below kcov and kmsan exit, which should be
harmless.

Link: https://lkml.kernel.org/r/20250319195436.1864415-1-mjguzik@gmail.com
Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Mateusz Guzik
2025-03-19 20:54:36 +01:00
committed by Andrew Morton
parent 3eff6a3e57
commit fe6f600c43
1 changed files with 32 additions and 36 deletions
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68
kernel/exit.c
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@@ -415,44 +415,30 @@ kill_orphaned_pgrp(struct task_struct *tsk, struct task_struct *parent)
}
}
static void coredump_task_exit(struct task_struct *tsk)
static void coredump_task_exit(struct task_struct *tsk,
struct core_state *core_state)
{
struct core_state *core_state;
struct core_thread self;
self.task = tsk;
if (self.task->flags & PF_SIGNALED)
self.next = xchg(&core_state->dumper.next, &self);
else
self.task = NULL;
/*
* Serialize with any possible pending coredump.
* We must hold siglock around checking core_state
* and setting PF_POSTCOREDUMP. The core-inducing thread
* will increment ->nr_threads for each thread in the
* group without PF_POSTCOREDUMP set.
* Implies mb(), the result of xchg() must be visible
* to core_state->dumper.
*/
spin_lock_irq(&tsk->sighand->siglock);
tsk->flags |= PF_POSTCOREDUMP;
core_state = tsk->signal->core_state;
spin_unlock_irq(&tsk->sighand->siglock);
if (core_state) {
struct core_thread self;
if (atomic_dec_and_test(&core_state->nr_threads))
complete(&core_state->startup);
self.task = current;
if (self.task->flags & PF_SIGNALED)
self.next = xchg(&core_state->dumper.next, &self);
else
self.task = NULL;
/*
* Implies mb(), the result of xchg() must be visible
* to core_state->dumper.
*/
if (atomic_dec_and_test(&core_state->nr_threads))
complete(&core_state->startup);
for (;;) {
set_current_state(TASK_IDLE|TASK_FREEZABLE);
if (!self.task) /* see coredump_finish() */
break;
schedule();
}
__set_current_state(TASK_RUNNING);
for (;;) {
set_current_state(TASK_IDLE|TASK_FREEZABLE);
if (!self.task) /* see coredump_finish() */
break;
schedule();
}
__set_current_state(TASK_RUNNING);
}
#ifdef CONFIG_MEMCG
@@ -876,6 +862,7 @@ static void synchronize_group_exit(struct task_struct *tsk, long code)
{
struct sighand_struct *sighand = tsk->sighand;
struct signal_struct *signal = tsk->signal;
struct core_state *core_state;
spin_lock_irq(&sighand->siglock);
signal->quick_threads--;
@@ -885,7 +872,19 @@ static void synchronize_group_exit(struct task_struct *tsk, long code)
signal->group_exit_code = code;
signal->group_stop_count = 0;
}
/*
* Serialize with any possible pending coredump.
* We must hold siglock around checking core_state
* and setting PF_POSTCOREDUMP. The core-inducing thread
* will increment ->nr_threads for each thread in the
* group without PF_POSTCOREDUMP set.
*/
tsk->flags |= PF_POSTCOREDUMP;
core_state = signal->core_state;
spin_unlock_irq(&sighand->siglock);
if (unlikely(core_state))
coredump_task_exit(tsk, core_state);
}
void __noreturn do_exit(long code)
@@ -894,15 +893,12 @@ void __noreturn do_exit(long code)
int group_dead;
WARN_ON(irqs_disabled());
synchronize_group_exit(tsk, code);
WARN_ON(tsk->plug);
kcov_task_exit(tsk);
kmsan_task_exit(tsk);
coredump_task_exit(tsk);
synchronize_group_exit(tsk, code);
ptrace_event(PTRACE_EVENT_EXIT, code);
user_events_exit(tsk);