target: Fix percpu_ref_put race in transport_lun_remove_cmd
This patch fixes a percpu_ref_put race for se_lun->lun_ref in
transport_lun_remove_cmd() where ->lun_ref could end up being
put more than once per command via different target completion
and fabric release contexts.
It adds a cmpxchg() for se_cmd->lun_ref_active to ensure that
percpu_ref_put() is only ever called once per se_cmd.
This bug was manifesting itself as a LUN shutdown regression
bug in >= v3.13 code, where percpu_ref_kill() would end up
hanging indefinately due to the incorrect percpu_ref count.
(Change se_cmd->lun_ref_active from bool -> int to force at
least a 4-byte cmpxchg with MIPS ll/sc ins. - Fengguang)
Reported-by: Tommy Apel <tommyapeldk@gmail.com>
Cc: Tommy Apel <tommyapeldk@gmail.com>
Cc: <stable@vger.kernel.org> #3.13+
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
index 51a9736..c50fd9f 100644
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -594,10 +594,11 @@
{
struct se_lun *lun = cmd->se_lun;
- if (!lun || !cmd->lun_ref_active)
+ if (!lun)
return;
- percpu_ref_put(&lun->lun_ref);
+ if (cmpxchg(&cmd->lun_ref_active, true, false))
+ percpu_ref_put(&lun->lun_ref);
}
void transport_cmd_finish_abort(struct se_cmd *cmd, int remove)
diff --git a/include/target/target_core_base.h b/include/target/target_core_base.h
index d284186..909dacb 100644
--- a/include/target/target_core_base.h
+++ b/include/target/target_core_base.h
@@ -552,7 +552,7 @@
void *priv;
/* Used for lun->lun_ref counting */
- bool lun_ref_active;
+ int lun_ref_active;
/* DIF related members */
enum target_prot_op prot_op;