From: Julian Wiedmann <jwi@xxxxxxxxxxxxx>
While reviewing
commit 936e6b85da04 ("scsi: zfcp: Fix panic on ERP timeout for previously
dismissed ERP action"),
I stumbled over zfcp_fsf_req_complete() and wondered whether it has
similar issues wrt concurrent modification of req->erp_action
by zfcp_erp_strategy_check_fsfreq().
But a closer look shows that both its two callers
[zfcp_fsf_reqid_check(), zfcp_fsf_req_dismiss_all()] remove the request
from the adapter's req_list under the req_list's lock.
Hence we can trust that if zfcp_erp_strategy_check_fsfreq() concurrently
looks up the corresponding req_id, it won't find this request and is thus
unable to modify it while it's being processed by zfcp_fsf_req_complete().
Add a code comment that hopefully makes this easier for future readers,
and condense the two accesses to ->erp_action that made me trip over
this code path in the first place.
Signed-off-by: Julian Wiedmann <jwi@xxxxxxxxxxxxx>
Reviewed-by: Steffen Maier <maier@xxxxxxxxxxxxx>
Reviewed-by: Benjamin Block <bblock@xxxxxxxxxxxxx>
Signed-off-by: Benjamin Block <bblock@xxxxxxxxxxxxx>
---
drivers/s390/scsi/zfcp_fsf.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/drivers/s390/scsi/zfcp_fsf.c b/drivers/s390/scsi/zfcp_fsf.c
index c795f22249d8..d9de26157da2 100644
--- a/drivers/s390/scsi/zfcp_fsf.c
+++ b/drivers/s390/scsi/zfcp_fsf.c
@@ -426,9 +426,14 @@ static void zfcp_fsf_protstatus_eval(struct zfcp_fsf_req *req)
* or it has been dismissed due to a queue shutdown, this function
* is called to process the completion status and trigger further
* events related to the FSF request.
+ * Caller must ensure that the request has been removed from
+ * adapter->req_list, to protect against concurrent modification
+ * by zfcp_erp_strategy_check_fsfreq().
*/
static void zfcp_fsf_req_complete(struct zfcp_fsf_req *req)
{
+ struct zfcp_erp_action *erp_action;
+
if (unlikely(zfcp_fsf_req_is_status_read_buffer(req))) {
zfcp_fsf_status_read_handler(req);
return;
@@ -439,8 +444,9 @@ static void zfcp_fsf_req_complete(struct zfcp_fsf_req *req)
zfcp_fsf_fsfstatus_eval(req);
req->handler(req);
- if (req->erp_action)
- zfcp_erp_notify(req->erp_action, 0);
+ erp_action = req->erp_action;
+ if (erp_action)
+ zfcp_erp_notify(erp_action, 0);
if (likely(req->status & ZFCP_STATUS_FSFREQ_CLEANUP))
zfcp_fsf_req_free(req);
--
2.26.2
