The patch titled
cpu-timers: assure to not iterate over all threads in fastpath_timer_check()
has been added to the -mm tree. Its filename is
cpu-timers-assure-to-not-iterate-over-all-threads-in-fastpath_timer_check.patch
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out what to do about this
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: cpu-timers: assure to not iterate over all threads in fastpath_timer_check()
From: Stanislaw Gruszka <sgruszka@xxxxxxxxxx>
Spread p->sighand->siglock locking scope to assure fastpath_timer_check()
never iterate over each threads. Without locking there is small
possibility that signal->cputimer will stop running while we write values
to signal->cputime_expires.
Calling thread_group_cputime() from fastpath_timer_check() is not only bad
because it is slow, also it is racy with __exit_signal() which can lead to
invalid signal->{s,u}time values.
Signed-off-by: Stanislaw Gruszka <sgruszka@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Hidetoshi Seto <seto.hidetoshi@xxxxxxxxxxxxxx>
Cc: Balbir Singh <balbir@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/posix-cpu-timers.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)
diff -puN kernel/posix-cpu-timers.c~cpu-timers-assure-to-not-iterate-over-all-threads-in-fastpath_timer_check kernel/posix-cpu-timers.c
--- a/kernel/posix-cpu-timers.c~cpu-timers-assure-to-not-iterate-over-all-threads-in-fastpath_timer_check
+++ a/kernel/posix-cpu-timers.c
@@ -549,7 +549,7 @@ static inline int expires_gt(cputime_t e
/*
* Insert the timer on the appropriate list before any timers that
* expire later. This must be called with the tasklist_lock held
- * for reading, and interrupts disabled.
+ * for reading, interrupts disabled and p->sighand->siglock taken.
*/
static void arm_timer(struct k_itimer *timer)
{
@@ -568,9 +568,6 @@ static void arm_timer(struct k_itimer *t
}
head += CPUCLOCK_WHICH(timer->it_clock);
- BUG_ON(!irqs_disabled());
- spin_lock(&p->sighand->siglock);
-
listpos = head;
list_for_each_entry(next, head, entry) {
if (cpu_time_before(timer->it_clock, nt->expires, next->expires))
@@ -605,8 +602,6 @@ static void arm_timer(struct k_itimer *t
break;
}
}
-
- spin_unlock(&p->sighand->siglock);
}
/*
@@ -719,7 +714,6 @@ int posix_cpu_timer_set(struct k_itimer
ret = TIMER_RETRY;
} else
list_del_init(&timer->it.cpu.entry);
- spin_unlock(&p->sighand->siglock);
/*
* We need to sample the current value to convert the new
@@ -773,6 +767,7 @@ int posix_cpu_timer_set(struct k_itimer
* disable this firing since we are already reporting
* it as an overrun (thanks to bump_cpu_timer above).
*/
+ spin_unlock(&p->sighand->siglock);
read_unlock(&tasklist_lock);
goto out;
}
@@ -792,6 +787,7 @@ int posix_cpu_timer_set(struct k_itimer
arm_timer(timer);
}
+ spin_unlock(&p->sighand->siglock);
read_unlock(&tasklist_lock);
/*
@@ -1205,6 +1201,7 @@ void posix_cpu_timer_schedule(struct k_i
goto out;
}
read_lock(&tasklist_lock); /* arm_timer needs it. */
+ spin_lock(&p->sighand->siglock);
} else {
read_lock(&tasklist_lock);
if (unlikely(p->signal == NULL)) {
@@ -1225,6 +1222,7 @@ void posix_cpu_timer_schedule(struct k_i
clear_dead_task(timer, now);
goto out_unlock;
}
+ spin_lock(&p->sighand->siglock);
cpu_timer_sample_group(timer->it_clock, p, &now);
bump_cpu_timer(timer, now);
/* Leave the tasklist_lock locked for the call below. */
@@ -1233,7 +1231,9 @@ void posix_cpu_timer_schedule(struct k_i
/*
* Now re-arm for the new expiry time.
*/
+ BUG_ON(!irqs_disabled());
arm_timer(timer);
+ spin_unlock(&p->sighand->siglock);
out_unlock:
read_unlock(&tasklist_lock);
_
Patches currently in -mm which might be from sgruszka@xxxxxxxxxx are
posix-cpu-timers-reset-expire-cache-when-no-timer-is-running.patch
cpu-timers-simplify-rlimit_cpu-handling.patch
cpu-timers-cleanup-arm_timer.patch
cpu-timers-return-correct-previous-timer-reload-value.patch
cpu-timers-change-sigev_none-timer-implementation.patch
cpu-timers-assure-to-not-iterate-over-all-threads-in-fastpath_timer_check.patch
cpu-timers-optimize-run_posix_cpu_timers.patch
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