diff options
author | Roland McGrath <roland@redhat.com> | 2005-10-20 05:21:23 (GMT) |
---|---|---|
committer | Linus Torvalds <torvalds@g5.osdl.org> | 2005-10-20 06:02:01 (GMT) |
commit | e03d13e985d48ac4885382c9e3b1510c78bd047f (patch) | |
tree | 04a124c1759f4b16e21fd04031ee9677fab58021 /kernel | |
parent | 3359b54c8c07338f3a863d1109b42eebccdcf379 (diff) | |
download | linux-e03d13e985d48ac4885382c9e3b1510c78bd047f.tar.xz |
[PATCH] Fix cpu timers exit deadlock and races
Oleg Nesterov reported an SMP deadlock. If there is a running timer
tracking a different process's CPU time clock when the process owning
the timer exits, we deadlock on tasklist_lock in posix_cpu_timer_del via
exit_itimers.
That code was using tasklist_lock to check for a race with __exit_signal
being called on the timer-target task and clearing its ->signal.
However, there is actually no such race. __exit_signal will have called
posix_cpu_timers_exit and posix_cpu_timers_exit_group before it does
that. Those will clear those k_itimer's association with the dying
task, so posix_cpu_timer_del will return early and never reach the code
in question.
In addition, posix_cpu_timer_del called from exit_itimers during execve
or directly from timer_delete in the process owning the timer can race
with an exiting timer-target task to cause a double put on timer-target
task struct. Make sure we always access cpu_timers lists with sighand
lock held.
Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Chris Wright <chrisw@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'kernel')
-rw-r--r-- | kernel/posix-cpu-timers.c | 28 |
1 files changed, 11 insertions, 17 deletions
diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c index 7a51a55..b3f3edc 100644 --- a/kernel/posix-cpu-timers.c +++ b/kernel/posix-cpu-timers.c @@ -387,25 +387,19 @@ int posix_cpu_timer_del(struct k_itimer *timer) if (unlikely(p == NULL)) return 0; + spin_lock(&p->sighand->siglock); if (!list_empty(&timer->it.cpu.entry)) { - read_lock(&tasklist_lock); - if (unlikely(p->signal == NULL)) { - /* - * We raced with the reaping of the task. - * The deletion should have cleared us off the list. - */ - BUG_ON(!list_empty(&timer->it.cpu.entry)); - } else { - /* - * Take us off the task's timer list. - */ - spin_lock(&p->sighand->siglock); - list_del(&timer->it.cpu.entry); - spin_unlock(&p->sighand->siglock); - } - read_unlock(&tasklist_lock); + /* + * Take us off the task's timer list. We don't need to + * take tasklist_lock and check for the task being reaped. + * If it was reaped, it already called posix_cpu_timers_exit + * and posix_cpu_timers_exit_group to clear all the timers + * that pointed to it. + */ + list_del(&timer->it.cpu.entry); + put_task_struct(p); } - put_task_struct(p); + spin_unlock(&p->sighand->siglock); return 0; } |