block: Prevent hang_check firing during long I/O

During long I/O operations, the hang_check timer may fire,
trigger stack dumps that unnecessarily alarm the user.

Eg.  hdparm --security-erase NULL /dev/sdb  ## can take *hours* to complete

So, if hang_check is armed, we should wake up periodically
to prevent it from triggering.  This patch uses a wake-up interval
equal to half the hang_check timer period, which keeps overhead low enough.

Signed-off-by: Mark Lord <mlord@pobox.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 8 insertions, 1 deletions

diff --git a/block/blk-exec.c b/block/blk-exec.c
index e1672f14840e..cf1456a02acd 100644
--- a/block/blk-exec.c
+++ b/block/blk-exec.c
@@ -80,6 +80,7 @@ int blk_execute_rq(struct request_queue *q, struct gendisk *bd_disk,
         DECLARE_COMPLETION_ONSTACK(wait);
         char sense[SCSI_SENSE_BUFFERSIZE];
         int err = 0;
+        unsigned long hang_check;
 
         /*
          * we need an extra reference to the request, so we can look at
@@ -95,7 +96,13 @@ int blk_execute_rq(struct request_queue *q, struct gendisk *bd_disk,
 
         rq->end_io_data = &wait;
         blk_execute_rq_nowait(q, bd_disk, rq, at_head, blk_end_sync_rq);
-        wait_for_completion(&wait);
+
+        /* Prevent hang_check timer from firing at us during very long I/O */
+        hang_check = sysctl_hung_task_timeout_secs;
+        if (hang_check)
+                while (!wait_for_completion_timeout(&wait, hang_check * (HZ/2)));
+        else
+                wait_for_completion(&wait);
 
         if (rq->errors)
                 err = -EIO;