linux-kernel - [PATCH 4.4 100/107] block: do not use interruptible wait anywhere

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Date:   Mon, 23 Jul 2018 14:42:34 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Bart Van Assche <bart.vanassche@....com>,
        Alan Jenkins <alan.christopher.jenkins@...il.com>,
        Jens Axboe <axboe@...nel.dk>,
        Sudip Mukherjee <sudipm.mukherjee@...il.com>
Subject: [PATCH 4.4 100/107] block: do not use interruptible wait anywhere

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Alan Jenkins <alan.christopher.jenkins@...il.com>

commit 1dc3039bc87ae7d19a990c3ee71cfd8a9068f428 upstream.

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:

# dd if=/dev/sda of=/dev/null iflag=direct & \
  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@....com>
Cc: stable@...r.kernel.org
Signed-off-by: Alan Jenkins <alan.christopher.jenkins@...il.com>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@...il.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 block/blk-core.c |   10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -651,21 +651,17 @@ EXPORT_SYMBOL(blk_alloc_queue);
 int blk_queue_enter(struct request_queue *q, gfp_t gfp)
 {
 	while (true) {
-		int ret;
-
 		if (percpu_ref_tryget_live(&q->q_usage_counter))
 			return 0;

 		if (!gfpflags_allow_blocking(gfp))
 			return -EBUSY;

-		ret = wait_event_interruptible(q->mq_freeze_wq,
-				!atomic_read(&q->mq_freeze_depth) ||
-				blk_queue_dying(q));
+		wait_event(q->mq_freeze_wq,
+			   !atomic_read(&q->mq_freeze_depth) ||
+			   blk_queue_dying(q));
 		if (blk_queue_dying(q))
 			return -ENODEV;
-		if (ret)
-			return ret;
 	}
 }