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Subject[PATCH 3.16.y-ckt 077/133] scsi: fix scsi_error_handler vs. scsi_host_dev_release race
Date
3.16.7-ckt18 -stable review patch.  If anyone has any objections, please let me know.

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

From: Michal Hocko <mhocko@suse.com>

commit 537b604c8b3aa8b96fe35f87dd085816552e294c upstream.

b9d5c6b7ef57 ("[SCSI] cleanup setting task state in
scsi_error_handler()") has introduced a race between scsi_error_handler
and scsi_host_dev_release resulting in the hang when the device goes
away because scsi_error_handler might miss a wake up:

CPU0 CPU1
scsi_error_handler scsi_host_dev_release
kthread_stop()
kthread_should_stop()
test_bit(KTHREAD_SHOULD_STOP)
set_bit(KTHREAD_SHOULD_STOP)
wake_up_process()
wait_for_completion()

set_current_state(TASK_INTERRUPTIBLE)
schedule()

The most straightforward solution seems to be to invert the ordering of
the set_current_state and kthread_should_stop.

The issue has been noticed during reboot test on a 3.0 based kernel but
the current code seems to be affected in the same way.

[jejb: additional comment added]
Reported-and-debugged-by: Mike Mayer <Mike.Meyer@teradata.com>
Signed-off-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: James Bottomley <JBottomley@Odin.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
drivers/scsi/scsi_error.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
index f0c7a970547f..48790f1dbf79 100644
--- a/drivers/scsi/scsi_error.c
+++ b/drivers/scsi/scsi_error.c
@@ -2154,8 +2154,17 @@ int scsi_error_handler(void *data)
* We never actually get interrupted because kthread_run
* disables signal delivery for the created thread.
*/
- while (!kthread_should_stop()) {
+ while (true) {
+ /*
+ * The sequence in kthread_stop() sets the stop flag first
+ * then wakes the process. To avoid missed wakeups, the task
+ * should always be in a non running state before the stop
+ * flag is checked
+ */
set_current_state(TASK_INTERRUPTIBLE);
+ if (kthread_should_stop())
+ break;
+
if ((shost->host_failed == 0 && shost->host_eh_scheduled == 0) ||
shost->host_failed != shost->host_busy) {
SCSI_LOG_ERROR_RECOVERY(1,

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