Russ, how about this patch instead? Can you verify whether or not
this fixes your issue? If so, I'll push it to Linus.
- Ted
>From 24c598b5abd466f2bab954d0cc8c225e0d3a2a74 Mon Sep 17 00:00:00 2001
From: Theodore Ts'o <ty...@mit.edu>
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" <ty...@mit.edu>
Reported-by: Russ Dill <russ.d...@gmail.com>
Cc: sta...@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 85e81ec..57d4b15 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -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;
}
--
1.7.12.rc0.22.gcdd159b
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