[PATCH 03/21] Clear host_eh_scheduled from inside the SCSI error handler

[Bart Van Assche <bvanassche@acm.org>]

The current protocol for scheduling the SCSI error handler explicitly
is as follows:
1. The LLD registers a transport layer that defines a eh_strategy_handler.
2. The LLD observes an error, sets variables that indicate the nature of the
   error and calls scsi_schedule_eh(). Currently only the ATA core and libsas
   use scsi_schedule_eh().
3. scsi_schedule_eh() increments host_eh_scheduled.
4. The SCSI error handling thread wakes up and invokes eh_strategy_handler.
5. After all errors have been handled and before the eh_strategy_handler
   implementation returns, host_eh_scheduled is cleared. This must be done
   in such a way that all errors that happened while the error handler was
   running are either handled or result in rerunning the error handler.

Making LLDs responsible for clearing host_eh_scheduled is error prone.
Hence clear host_eh_scheduled from inside the SCSI error handler. A side
effect of this patch is that if scsi_schedule_eh() is called while the
SCSI error handler is active that it will be reactivated immediately.

Cc: Hannes Reinecke <hare@suse.de>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: John Garry <john.garry@huawei.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 drivers/scsi/scsi_error.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
index c6cd5a8e5c85..665cc44d8877 100644
--- a/drivers/scsi/scsi_error.c
+++ b/drivers/scsi/scsi_error.c
@@ -2242,6 +2242,13 @@ int scsi_error_handler(void *data)
 			continue;
 		}
 
+		/*
+		 * Clear host_eh_scheduled before handling any errors such that
+		 * calling scsi_schedule_eh() while errors are being handled
+		 * causes the error handler to be rerun.
+		 */
+		shost->host_eh_scheduled = 0;
+
 		if (shost->transportt->eh_strategy_handler)
 			shost->transportt->eh_strategy_handler(shost);
 		else