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author | Oleg Nesterov <oleg@tv-sign.ru> | 2005-10-24 18:29:58 +0400 |
---|---|---|
committer | Linus Torvalds <torvalds@g5.osdl.org> | 2005-10-24 08:13:14 -0700 |
commit | a69ac4a78d8bd9e1ec478bd7297d4f047fcd44a8 (patch) | |
tree | a56edf4f69cc01c6d4b7b3eeee3646c7ea9810df /kernel/posix-cpu-timers.c | |
parent | ca531a0a5e01e5122f67cb6aca8fcbfc70e18e0b (diff) | |
download | linux-stable-a69ac4a78d8bd9e1ec478bd7297d4f047fcd44a8.tar.gz linux-stable-a69ac4a78d8bd9e1ec478bd7297d4f047fcd44a8.tar.bz2 linux-stable-a69ac4a78d8bd9e1ec478bd7297d4f047fcd44a8.zip |
[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>
Diffstat (limited to 'kernel/posix-cpu-timers.c')
-rw-r--r-- | kernel/posix-cpu-timers.c | 12 |
1 files changed, 8 insertions, 4 deletions
diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c index 92a038064628..b15462b17a58 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; } |