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authorOleg Nesterov <oleg@tv-sign.ru>2006-06-15 20:11:43 +0400
committerLinus Torvalds <torvalds@g5.osdl.org>2006-06-17 10:52:13 -0700
commit30f1e3dd8c72abda343bcf415f7d8894a02b4290 (patch)
tree68ef326814e3b8e6ba0159cc451cef4b71695ea3 /kernel/posix-cpu-timers.c
parent[PATCH] check_process_timers: fix possible lockup (diff)
downloadlinux-dev-30f1e3dd8c72abda343bcf415f7d8894a02b4290.tar.xz
linux-dev-30f1e3dd8c72abda343bcf415f7d8894a02b4290.zip
[PATCH] run_posix_cpu_timers: remove a bogus BUG_ON()
do_exit() clears ->it_##clock##_expires, but nothing prevents another cpu to attach the timer to exiting process after that. arm_timer() tries to protect against this race, but the check is racy. After exit_notify() does 'write_unlock_irq(&tasklist_lock)' and before do_exit() calls 'schedule() local timer interrupt can find tsk->exit_state != 0. If that state was EXIT_DEAD (or another cpu does sys_wait4) interrupted task has ->signal == NULL. At this moment exiting task has no pending cpu timers, they were cleanuped in __exit_signal()->posix_cpu_timers_exit{,_group}(), so we can just return from irq. John Stultz recently confirmed this bug, see http://marc.theaimsgroup.com/?l=linux-kernel&m=115015841413687 Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to '')
-rw-r--r--kernel/posix-cpu-timers.c36
1 files changed, 18 insertions, 18 deletions
diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index 9d9169aa2e24..4882bf1e094a 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -1288,30 +1288,30 @@ void run_posix_cpu_timers(struct task_struct *tsk)
#undef UNEXPIRED
- BUG_ON(tsk->exit_state);
-
/*
* Double-check with locks held.
*/
read_lock(&tasklist_lock);
- spin_lock(&tsk->sighand->siglock);
+ if (likely(tsk->signal != NULL)) {
+ spin_lock(&tsk->sighand->siglock);
- /*
- * Here we take off tsk->cpu_timers[N] and tsk->signal->cpu_timers[N]
- * all the timers that are firing, and put them on the firing list.
- */
- check_thread_timers(tsk, &firing);
- check_process_timers(tsk, &firing);
+ /*
+ * Here we take off tsk->cpu_timers[N] and tsk->signal->cpu_timers[N]
+ * all the timers that are firing, and put them on the firing list.
+ */
+ check_thread_timers(tsk, &firing);
+ check_process_timers(tsk, &firing);
- /*
- * We must release these locks before taking any timer's lock.
- * There is a potential race with timer deletion here, as the
- * siglock now protects our private firing list. We have set
- * the firing flag in each timer, so that a deletion attempt
- * that gets the timer lock before we do will give it up and
- * spin until we've taken care of that timer below.
- */
- spin_unlock(&tsk->sighand->siglock);
+ /*
+ * We must release these locks before taking any timer's lock.
+ * There is a potential race with timer deletion here, as the
+ * siglock now protects our private firing list. We have set
+ * the firing flag in each timer, so that a deletion attempt
+ * that gets the timer lock before we do will give it up and
+ * spin until we've taken care of that timer below.
+ */
+ spin_unlock(&tsk->sighand->siglock);
+ }
read_unlock(&tasklist_lock);
/*