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Commit b9809552 authored by Theodore Ts'o's avatar Theodore Ts'o
Browse files

random: fix locking dependency with the tasklist_lock 



Commit 61337054 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: default avatar"Theodore Ts'o" <tytso@mit.edu>
Reported-by: default avatarRuss Dill <Russ.Dill@gmail.com>
Cc: stable@kernel.org
parent 19f949f5

drivers/char/random.c

+8 −4
Original line number Diff line number Diff line
@@ -852,6 +852,7 @@ 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);
@@ -873,10 +874,8 @@ 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 %zu entropy credits from %s%s\n",
@@ -884,6 +883,11 @@ 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;

}