| From | Luis Henriques <> | Subject | [PATCH 67/88] random: fix locking dependency with the tasklist_lock | Date | Thu, 14 Mar 2013 10:36:00 +0000 |
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3.5.7.8 -stable review patch. If anyone has any objections, please let me know.
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From: Theodore Ts'o <tytso@mit.edu>
commit b980955236922ae6106774511c5c05003d3ad225 upstream.
Commit 6133705494bb introduced a circular lock dependency because posix_cpu_timers_exit() is called by release_task(), which is holding a writer lock on tasklist_lock, and this can cause a deadlock since kill_fasync() gets called with nonblocking_pool.lock taken.
There's no reason why kill_fasync() needs to be taken while the random pool is locked, so move it out to fix this locking dependency.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu> Reported-by: Russ Dill <Russ.Dill@gmail.com> Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- drivers/char/random.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-)
diff --git a/drivers/char/random.c b/drivers/char/random.c index d98b2a6..91abbc4 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -855,6 +855,7 @@ static size_t account(struct entropy_store *r, size_t nbytes, int min, int reserved) { unsigned long flags; + int wakeup_write = 0; /* Hold lock while accounting */ spin_lock_irqsave(&r->lock, flags); @@ -876,10 +877,8 @@ static size_t account(struct entropy_store *r, size_t nbytes, int min, else r->entropy_count = reserved; - if (r->entropy_count < random_write_wakeup_thresh) { - wake_up_interruptible(&random_write_wait); - kill_fasync(&fasync, SIGIO, POLL_OUT); - } + if (r->entropy_count < random_write_wakeup_thresh) + wakeup_write = 1; } DEBUG_ENT("debiting %d entropy credits from %s%s\n", @@ -887,6 +886,11 @@ static size_t account(struct entropy_store *r, size_t nbytes, int min, spin_unlock_irqrestore(&r->lock, flags); + if (wakeup_write) { + wake_up_interruptible(&random_write_wait); + kill_fasync(&fasync, SIGIO, POLL_OUT); + } + return nbytes; } -- 1.8.1.2
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