random: fix locking dependency with the tasklist_lock (b9809552) · Commits · 戴 / test

Commit 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> Cc: stable@kernel.org

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;
		}

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