[SRU,Bionic,1/1] block: do not use interruptible wait anywhere

Message ID bccce17c618be94a6d9afcb39e434a4c4d4969fe.1528989676.git.joseph.salisbury@canonical.com
State New
Headers show
Series
  • block: do not use interruptible wait anywhere
Related show

Commit Message

Joseph Salisbury June 29, 2018, 1:39 p.m.
From: Alan Jenkins <alan.christopher.jenkins@gmail.com>

BugLink: http://bugs.launchpad.net/bugs/1776887

When blk_queue_enter() waits for a queue to unfreeze, or unset the
PREEMPT_ONLY flag, do not allow it to be interrupted by a signal.

The PREEMPT_ONLY flag was introduced later in commit 3a0a529971ec
("block, scsi: Make SCSI quiesce and resume work reliably").  Note the SCSI
device is resumed asynchronously, i.e. after un-freezing userspace tasks.

So that commit exposed the bug as a regression in v4.15.  A mysterious
SIGBUS (or -EIO) sometimes happened during the time the device was being
resumed.  Most frequently, there was no kernel log message, and we saw Xorg
or Xwayland killed by SIGBUS.[1]

[1] E.g. https://bugzilla.redhat.com/show_bug.cgi?id=1553979

Without this fix, I get an IO error in this test:

  while killall -SIGUSR1 dd; do sleep 0.1; done & \
  echo mem > /sys/power/state ; \
  sleep 5; killall dd  # stop after 5 seconds

The interruptible wait was added to blk_queue_enter in
commit 3ef28e83ab15 ("block: generic request_queue reference counting").
Before then, the interruptible wait was only in blk-mq, but I don't think
it could ever have been correct.

Reviewed-by: Bart Van Assche <bart.vanassche@wdc.com>
Cc: stable@vger.kernel.org
Signed-off-by: Alan Jenkins <alan.christopher.jenkins@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
(cherry picked from commit 1dc3039bc87ae7d19a990c3ee71cfd8a9068f428)
Signed-off-by: Joseph Salisbury <joseph.salisbury@canonical.com>
---
 block/blk-core.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

Patch

diff --git a/block/blk-core.c b/block/blk-core.c
index 322c47f..246ea84 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -821,7 +821,6 @@  int blk_queue_enter(struct request_queue *q, blk_mq_req_flags_t flags)
 
 	while (true) {
 		bool success = false;
-		int ret;
 
 		rcu_read_lock();
 		if (percpu_ref_tryget_live(&q->q_usage_counter)) {
@@ -853,14 +852,12 @@  int blk_queue_enter(struct request_queue *q, blk_mq_req_flags_t flags)
 		 */
 		smp_rmb();
 
-		ret = wait_event_interruptible(q->mq_freeze_wq,
-				(atomic_read(&q->mq_freeze_depth) == 0 &&
-				 (preempt || !blk_queue_preempt_only(q))) ||
-				blk_queue_dying(q));
+		wait_event(q->mq_freeze_wq,
+			   (atomic_read(&q->mq_freeze_depth) == 0 &&
+			    (preempt || !blk_queue_preempt_only(q))) ||
+			   blk_queue_dying(q));
 		if (blk_queue_dying(q))
 			return -ENODEV;
-		if (ret)
-			return ret;
 	}
 }