From 537b604c8b3aa8b96fe35f87dd085816552e294c Mon Sep 17 00:00:00 2001 From: Michal Hocko Date: Thu, 27 Aug 2015 20:16:37 +0200 Subject: [PATCH] scsi: fix scsi_error_handler vs. scsi_host_dev_release race 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] Cc: # 3.6+ Reported-and-debugged-by: Mike Mayer Signed-off-by: Michal Hocko Reviewed-by: Dan Williams Reviewed-by: Hannes Reinecke Signed-off-by: James Bottomley --- 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 410911c31c67..b5bbc122c414 100644 --- a/drivers/scsi/scsi_error.c +++ b/drivers/scsi/scsi_error.c @@ -2179,8 +2179,17 @@ 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 != atomic_read(&shost->host_busy)) { SCSI_LOG_ERROR_RECOVERY(1, -- 2.20.1