iscsi-target: deadlock because of iscsit_get_tpg()

Hello,

Our tool reports a potential double lock because of quite strange code in iscsit_get_tpg().

drivers/target/iscsi/iscsi_target_tpg.c:
int iscsit_get_tpg(
struct iscsi_portal_group *tpg)

{
	int ret;

	ret = mutex_lock_interruptible(&tpg->tpg_access_lock);
	return ((ret != 0) || signal_pending(current)) ? -1 : 0;
}

If mutex_lock_interruptible() successfully acquires the mutex, but there is a pending signal, the function returns error, but it leaves the mutex held. Callers do not expect such behaviour that can lead to a deadlock.

Why the check for pending signal is needed here?

Found by Linux Driver Verification project (linuxtesting.org).

Similar dangerous pattern presents in a couple of other places:

drivers/target/iscsi/iscsi_target.c:
int iscsit_access_np(struct iscsi_np *np, struct iscsi_portal_group *tpg) {
...

	ret = down_interruptible(&tpg->np_login_sem);
	if ((ret != 0) || signal_pending(current))
		return -1;

drivers/target/target_core_sbc.c:
static sense_reason_t
sbc_compare_and_write(struct se_cmd *cmd)
{
...

	rc = down_interruptible(&dev->caw_sem);
	if ((rc != 0) || signal_pending(current)) {
		cmd->transport_complete_callback = NULL;
		return TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
	}

--
Alexey Khoroshilov
Linux Verification Center, ISPRAS

Hi Alexey,

Once upon a time, this was an un-interruptible lock. The signal pending was a check to allow userspace to break out of the operation with SIGINT.

AFAICT, there's no reason why this is necessary anymore.

Ditto on these.

Applying the following patch to target-pending/master.

Thank you,

--nab

index 34871a6..74e6114 100644
@@ -230,7 +230,7 @@ int iscsit_access_np(struct iscsi_np *np, struct iscsi_portal_group *tpg)
         * Here we serialize access across the TIQN+TPG Tuple.
         */
        ret = down_interruptible(&tpg->np_login_sem);
-       if ((ret != 0) || signal_pending(current))
+       if (ret != 0)
                return -1;
 
        spin_lock_bh(&tpg->tpg_state_lock);

index e8a2408..5e3295f 100644
@@ -161,10 +161,7 @@ struct iscsi_portal_group *iscsit_get_tpg_from_np(
 int iscsit_get_tpg(
        struct iscsi_portal_group *tpg)
 {
-       int ret;
-
-       ret = mutex_lock_interruptible(&tpg->tpg_access_lock);
-       return ((ret != 0) || signal_pending(current)) ? -1 : 0;
+       return mutex_lock_interruptible(&tpg->tpg_access_lock);
 }
 
 void iscsit_put_tpg(struct iscsi_portal_group *tpg)

index 8855781..733824e 100644
@@ -568,7 +568,7 @@ sbc_compare_and_write(struct se_cmd *cmd)
         * comparision using SGLs at cmd->t_bidi_data_sg..
         */
        rc = down_interruptible(&dev->caw_sem);
-       if ((rc != 0) || signal_pending(current)) {
+       if (rc != 0) {
                cmd->transport_complete_callback = NULL;
                return TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
        }