From db136ed6aa4c7c2c330e2a53751d044544641345 Mon Sep 17 00:00:00 2001 From: Theodore Ts'o Date: Mon, 4 Mar 2013 11:59:12 -0500 Subject: [PATCH] random: fix locking dependency with the tasklist_lock 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" Reported-by: Russ Dill Cc: stable@kernel.org --- 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 b6ffae1b15f9..64bc10a04ca3 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -879,6 +879,7 @@ 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); @@ -908,10 +909,8 @@ retry: goto retry; } - if (entropy_count < random_write_wakeup_thresh) { - wake_up_interruptible(&random_write_wait); - kill_fasync(&fasync, SIGIO, POLL_OUT); - } + if (entropy_count < random_write_wakeup_thresh) + wakeup_write = 1; } DEBUG_ENT("debiting %zu entropy credits from %s%s\n", @@ -919,6 +918,11 @@ retry: spin_unlock_irqrestore(&r->lock, flags); + if (wakeup_write) { + wake_up_interruptible(&random_write_wait); + kill_fasync(&fasync, SIGIO, POLL_OUT); + } + return nbytes; }