[PATCHv2 2/2] scsi: set timed out out mq requests to complete

Keith Busch
2018-07-23T14:37:51Z

The scsi block layer requires requests claimed by the error handling be
completed by the error handler. A previous commit allowed completions
to proceed for blk-mq, breaking that assumption.

This patch prevents completions that may race with the timeout handler
by marking the state to complete, restoring the previous behavior.

Fixes: 12f5b931 ("blk-mq: Remove generation seqeunce")
Signed-off-by: Keith Busch <keith.busch@intel.com>
---
v1 -> v2:

Document why this is necessary in code comments.

Update to API's changed return value

drivers/scsi/scsi_error.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)

diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
index 8932ae81a15a..2715cdaa669c 100644
--- a/drivers/scsi/scsi_error.c
+++ b/drivers/scsi/scsi_error.c
@@ -296,6 +296,20 @@ enum blk_eh_timer_return scsi_times_out(struct request *req)
rtn = host->hostt->eh_timed_out(scmd);

if (rtn == BLK_EH_DONE) {
+ /*
+ * For blk-mq, we must set the request state to complete now
+ * before sending the request to the scsi error handler. This
+ * will prevent a use-after-free in the event the LLD manages
+ * to complete the request before the error handler finishes
+ * processing this timed out request.
+ *
+ * If the request was already completed, then the LLD beat the
+ * time out handler from transferring the request to the scsi
+ * error handler. In that case we can return immediately as no
+ * further action is required.
+ */
+ if (req->q->mq_ops && !blk_mq_mark_complete(req))
+ return rtn;
if (scsi_abort_command(scmd) != SUCCESS) {
set_host_byte(scmd, DID_TIME_OUT);
scsi_eh_scmd_add(scmd);
--
2.14.4