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authorOleg Nesterov <oleg@tv-sign.ru>2005-10-24 18:29:58 +0400
committerLinus Torvalds <torvalds@g5.osdl.org>2005-10-24 08:13:14 -0700
commita69ac4a78d8bd9e1ec478bd7297d4f047fcd44a8 (patch)
treea56edf4f69cc01c6d4b7b3eeee3646c7ea9810df
parentca531a0a5e01e5122f67cb6aca8fcbfc70e18e0b (diff)
[PATCH] posix-timers: fix posix_cpu_timer_set() vs run_posix_cpu_timers() race
This might be harmless, but looks like a race from code inspection (I was unable to trigger it). I must admit, I don't understand why we can't return TIMER_RETRY after 'spin_unlock(&p->sighand->siglock)' without doing bump_cpu_timer(), but this is what original code does. posix_cpu_timer_set: read_lock(&tasklist_lock); spin_lock(&p->sighand->siglock); list_del_init(&timer->it.cpu.entry); spin_unlock(&p->sighand->siglock); We are probaly deleting the timer from run_posix_cpu_timers's 'firing' local list_head while run_posix_cpu_timers() does list_for_each_safe. Various bad things can happen, for example we can just delete this timer so that list_for_each() will not notice it and run_posix_cpu_timers() will not reset '->firing' flag. In that case, .... if (timer->it.cpu.firing) { read_unlock(&tasklist_lock); timer->it.cpu.firing = -1; return TIMER_RETRY; } sys_timer_settime() goes to 'retry:', calls posix_cpu_timer_set() again, it returns TIMER_RETRY ... Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
-rw-r--r--kernel/posix-cpu-timers.c12
1 files changed, 8 insertions, 4 deletions
diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index 92a03806462..b15462b17a5 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -730,9 +730,15 @@ int posix_cpu_timer_set(struct k_itimer *timer, int flags,
* Disarm any old timer after extracting its expiry time.
*/
BUG_ON(!irqs_disabled());
+
+ ret = 0;
spin_lock(&p->sighand->siglock);
old_expires = timer->it.cpu.expires;
- list_del_init(&timer->it.cpu.entry);
+ if (unlikely(timer->it.cpu.firing)) {
+ timer->it.cpu.firing = -1;
+ ret = TIMER_RETRY;
+ } else
+ list_del_init(&timer->it.cpu.entry);
spin_unlock(&p->sighand->siglock);
/*
@@ -780,7 +786,7 @@ int posix_cpu_timer_set(struct k_itimer *timer, int flags,
}
}
- if (unlikely(timer->it.cpu.firing)) {
+ if (unlikely(ret)) {
/*
* We are colliding with the timer actually firing.
* Punt after filling in the timer's old value, and
@@ -788,8 +794,6 @@ int posix_cpu_timer_set(struct k_itimer *timer, int flags,
* it as an overrun (thanks to bump_cpu_timer above).
*/
read_unlock(&tasklist_lock);
- timer->it.cpu.firing = -1;
- ret = TIMER_RETRY;
goto out;
}