iscsi-target: Fix mutex_trylock usage in iscsit_increment_maxcmdsn

This patch fixes a >= v3.10 regression bug with mutex_trylock() usage
within iscsit_increment_maxcmdsn(), that was originally added to allow
for a special case where ->cmdsn_mutex was already held from the
iscsit_execute_cmd() exception path for ib_isert.

When !mutex_trylock() was occuring under contention during normal RX/TX
process context codepaths, the bug was manifesting itself as the following
protocol error:

  Received CmdSN: 0x000fcbb7 is greater than MaxCmdSN: 0x000fcbb6, protocol error.
  Received CmdSN: 0x000fcbb8 is greater than MaxCmdSN: 0x000fcbb6, protocol error.

This patch simply avoids the direct ib_isert callback in lio_queue_status()
for the special iscsi_execute_cmd() exception cases, that allows the problematic
mutex_trylock() usage in iscsit_increment_maxcmdsn() to go away.

Reported-by: Moussa Ba <moussaba@micron.com>
Tested-by: Moussa Ba <moussaba@micron.com>
Cc: <stable@vger.kernel.org> # v3.10+
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

1 files changed, 1 insertions, 5 deletions

diff --git a/drivers/target/iscsi/iscsi_target_device.c b/drivers/target/iscsi/iscsi_target_device.c
index 6c7a5104a4cd..7087c736daa5 100644
--- a/drivers/target/iscsi/iscsi_target_device.c
+++ b/drivers/target/iscsi/iscsi_target_device.c
@@ -58,11 +58,7 @@ void iscsit_increment_maxcmdsn(struct iscsi_cmd *cmd, struct iscsi_session *sess
 
         cmd->maxcmdsn_inc = 1;
 
-        if (!mutex_trylock(&sess->cmdsn_mutex)) {
-                sess->max_cmd_sn += 1;
-                pr_debug("Updated MaxCmdSN to 0x%08x\n", sess->max_cmd_sn);
-                return;
-        }
+        mutex_lock(&sess->cmdsn_mutex);
         sess->max_cmd_sn += 1;
         pr_debug("Updated MaxCmdSN to 0x%08x\n", sess->max_cmd_sn);
         mutex_unlock(&sess->cmdsn_mutex);