target: Fix LUN_RESET active I/O handling for ACK_KREF

This patch fixes a NULL pointer se_cmd->cmd_kref < 0
refcount bug during TMR LUN_RESET with active se_cmd
I/O, that can be triggered during se_cmd descriptor
shutdown + release via core_tmr_drain_state_list() code.

To address this bug, add common __target_check_io_state()
helper for ABORT_TASK + LUN_RESET w/ CMD_T_COMPLETE
checking, and set CMD_T_ABORTED + obtain ->cmd_kref for
both cases ahead of last target_put_sess_cmd() after
TFO->aborted_task() -> transport_cmd_finish_abort()
callback has completed.

It also introduces SCF_ACK_KREF to determine when
transport_cmd_finish_abort() needs to drop the second
extra reference, ahead of calling target_put_sess_cmd()
for the final kref_put(&se_cmd->cmd_kref).

It also updates transport_cmd_check_stop() to avoid
holding se_cmd->t_state_lock while dropping se_cmd
device state via target_remove_from_state_list(), now
that core_tmr_drain_state_list() is holding the
se_device lock while checking se_cmd state from
within TMR logic.

Finally, move transport_put_cmd() release of SGL +
TMR + extended CDB memory into target_free_cmd_mem()
in order to avoid potential resource leaks in TMR
ABORT_TASK + LUN_RESET code-paths.  Also update
target_release_cmd_kref() accordingly.

Reviewed-by: Quinn Tran <quinn.tran@qlogic.com>
Cc: Himanshu Madhani <himanshu.madhani@qlogic.com>
Cc: Sagi Grimberg <sagig@mellanox.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Andy Grover <agrover@redhat.com>
Cc: Mike Christie <mchristi@redhat.com>
Cc: stable@vger.kernel.org # 3.10+
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

2 files changed, 75 insertions, 61 deletions

diff --git a/drivers/target/target_core_tmr.c b/drivers/target/target_core_tmr.c
index fcdcb117c60d..fb3decc28589 100644
--- a/drivers/target/target_core_tmr.c
+++ b/drivers/target/target_core_tmr.c
@@ -107,6 +107,34 @@ static int target_check_cdb_and_preempt(struct list_head *list,
         return 1;
 }
 
+static bool __target_check_io_state(struct se_cmd *se_cmd)
+{
+        struct se_session *sess = se_cmd->se_sess;
+
+        assert_spin_locked(&sess->sess_cmd_lock);
+        WARN_ON_ONCE(!irqs_disabled());
+        /*
+         * If command already reached CMD_T_COMPLETE state within
+         * target_complete_cmd(), this se_cmd has been passed to
+         * fabric driver and will not be aborted.
+         *
+         * Otherwise, obtain a local se_cmd->cmd_kref now for TMR
+         * ABORT_TASK + LUN_RESET for CMD_T_ABORTED processing as
+         * long as se_cmd->cmd_kref is still active unless zero.
+         */
+        spin_lock(&se_cmd->t_state_lock);
+        if (se_cmd->transport_state & CMD_T_COMPLETE) {
+                pr_debug("Attempted to abort io tag: %llu already complete,"
+                        " skipping\n", se_cmd->tag);
+                spin_unlock(&se_cmd->t_state_lock);
+                return false;
+        }
+        se_cmd->transport_state |= CMD_T_ABORTED;
+        spin_unlock(&se_cmd->t_state_lock);
+
+        return kref_get_unless_zero(&se_cmd->cmd_kref);
+}
+
 void core_tmr_abort_task(
         struct se_device *dev,
         struct se_tmr_req *tmr,
@@ -130,34 +158,22 @@ void core_tmr_abort_task(
                 if (tmr->ref_task_tag != ref_tag)
                         continue;
 
-                if (!kref_get_unless_zero(&se_cmd->cmd_kref))
-                        continue;
-
                 printk("ABORT_TASK: Found referenced %s task_tag: %llu\n",
                         se_cmd->se_tfo->get_fabric_name(), ref_tag);
 
-                spin_lock(&se_cmd->t_state_lock);
-                if (se_cmd->transport_state & CMD_T_COMPLETE) {
-                        printk("ABORT_TASK: ref_tag: %llu already complete,"
-                               " skipping\n", ref_tag);
-                        spin_unlock(&se_cmd->t_state_lock);
+                if (!__target_check_io_state(se_cmd)) {
                         spin_unlock_irqrestore(&se_sess->sess_cmd_lock, flags);
-
                         target_put_sess_cmd(se_cmd);
-
                         goto out;
                 }
-                se_cmd->transport_state |= CMD_T_ABORTED;
-                spin_unlock(&se_cmd->t_state_lock);
-
                 list_del_init(&se_cmd->se_cmd_list);
                 spin_unlock_irqrestore(&se_sess->sess_cmd_lock, flags);
 
                 cancel_work_sync(&se_cmd->work);
                 transport_wait_for_tasks(se_cmd);
 
-                target_put_sess_cmd(se_cmd);
                 transport_cmd_finish_abort(se_cmd, true);
+                target_put_sess_cmd(se_cmd);
 
                 printk("ABORT_TASK: Sending TMR_FUNCTION_COMPLETE for"
                                 " ref_tag: %llu\n", ref_tag);
@@ -242,8 +258,10 @@ static void core_tmr_drain_state_list(
         struct list_head *preempt_and_abort_list)
 {
         LIST_HEAD(drain_task_list);
+        struct se_session *sess;
         struct se_cmd *cmd, *next;
         unsigned long flags;
+        int rc;
 
         /*
          * Complete outstanding commands with TASK_ABORTED SAM status.
@@ -282,6 +300,16 @@ static void core_tmr_drain_state_list(
                 if (prout_cmd == cmd)
                         continue;
 
+                sess = cmd->se_sess;
+                if (WARN_ON_ONCE(!sess))
+                        continue;
+
+                spin_lock(&sess->sess_cmd_lock);
+                rc = __target_check_io_state(cmd);
+                spin_unlock(&sess->sess_cmd_lock);
+                if (!rc)
+                        continue;
+
                 list_move_tail(&cmd->state_list, &drain_task_list);
                 cmd->state_active = false;
         }
@@ -289,7 +317,7 @@ static void core_tmr_drain_state_list(
 
         while (!list_empty(&drain_task_list)) {
                 cmd = list_entry(drain_task_list.next, struct se_cmd, state_list);
-                list_del(&cmd->state_list);
+                list_del_init(&cmd->state_list);
 
                 pr_debug("LUN_RESET: %s cmd: %p"
                         " ITT/CmdSN: 0x%08llx/0x%08x, i_state: %d, t_state: %d"
@@ -313,16 +341,11 @@ static void core_tmr_drain_state_list(
                  * loop above, but we do it down here given that
                  * cancel_work_sync may block.
                  */
-                if (cmd->t_state == TRANSPORT_COMPLETE)
-                        cancel_work_sync(&cmd->work);
-
-                spin_lock_irqsave(&cmd->t_state_lock, flags);
-                target_stop_cmd(cmd, &flags);
-
-                cmd->transport_state |= CMD_T_ABORTED;
-                spin_unlock_irqrestore(&cmd->t_state_lock, flags);
+                cancel_work_sync(&cmd->work);
+                transport_wait_for_tasks(cmd);
 
                 core_tmr_handle_tas_abort(tmr_nacl, cmd, tas);
+                target_put_sess_cmd(cmd);
         }
 }
 
diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
index 9f3608e10f25..af52f8bd8954 100644
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -534,9 +534,6 @@ void transport_deregister_session(struct se_session *se_sess)
 }
 EXPORT_SYMBOL(transport_deregister_session);
 
-/*
- * Called with cmd->t_state_lock held.
- */
 static void target_remove_from_state_list(struct se_cmd *cmd)
 {
         struct se_device *dev = cmd->se_dev;
@@ -561,10 +558,6 @@ static int transport_cmd_check_stop(struct se_cmd *cmd, bool remove_from_lists,
 {
         unsigned long flags;
 
-        spin_lock_irqsave(&cmd->t_state_lock, flags);
-        if (write_pending)
-                cmd->t_state = TRANSPORT_WRITE_PENDING;
-
         if (remove_from_lists) {
                 target_remove_from_state_list(cmd);
 
@@ -574,6 +567,10 @@ static int transport_cmd_check_stop(struct se_cmd *cmd, bool remove_from_lists,
                 cmd->se_lun = NULL;
         }
 
+        spin_lock_irqsave(&cmd->t_state_lock, flags);
+        if (write_pending)
+                cmd->t_state = TRANSPORT_WRITE_PENDING;
+
         /*
          * Determine if frontend context caller is requesting the stopping of
          * this command for frontend exceptions.
@@ -627,6 +624,8 @@ static void transport_lun_remove_cmd(struct se_cmd *cmd)
 
 void transport_cmd_finish_abort(struct se_cmd *cmd, int remove)
 {
+        bool ack_kref = (cmd->se_cmd_flags & SCF_ACK_KREF);
+
         if (cmd->se_cmd_flags & SCF_SE_LUN_CMD)
                 transport_lun_remove_cmd(cmd);
         /*
@@ -638,7 +637,7 @@ void transport_cmd_finish_abort(struct se_cmd *cmd, int remove)
 
         if (transport_cmd_check_stop_to_fabric(cmd))
                 return;
-        if (remove)
+        if (remove && ack_kref)
                 transport_put_cmd(cmd);
 }
 
@@ -706,7 +705,7 @@ void target_complete_cmd(struct se_cmd *cmd, u8 scsi_status)
          * Check for case where an explicit ABORT_TASK has been received
          * and transport_wait_for_tasks() will be waiting for completion..
          */
-        if (cmd->transport_state & CMD_T_ABORTED &&
+        if (cmd->transport_state & CMD_T_ABORTED ||
             cmd->transport_state & CMD_T_STOP) {
                 spin_unlock_irqrestore(&cmd->t_state_lock, flags);
                 complete_all(&cmd->t_transport_stop_comp);
@@ -2222,20 +2221,14 @@ static inline void transport_free_pages(struct se_cmd *cmd)
 }
 
 /**
- * transport_release_cmd - free a command
- * @cmd:       command to free
+ * transport_put_cmd - release a reference to a command
+ * @cmd:       command to release
  *
- * This routine unconditionally frees a command, and reference counting
- * or list removal must be done in the caller.
+ * This routine releases our reference to the command and frees it if possible.
  */
-static int transport_release_cmd(struct se_cmd *cmd)
+static int transport_put_cmd(struct se_cmd *cmd)
 {
         BUG_ON(!cmd->se_tfo);
-
-        if (cmd->se_cmd_flags & SCF_SCSI_TMR_CDB)
-                core_tmr_release_req(cmd->se_tmr_req);
-        if (cmd->t_task_cdb != cmd->__t_task_cdb)
-                kfree(cmd->t_task_cdb);
         /*
          * If this cmd has been setup with target_get_sess_cmd(), drop
          * the kref and call ->release_cmd() in kref callback.
@@ -2243,18 +2236,6 @@ static int transport_release_cmd(struct se_cmd *cmd)
         return target_put_sess_cmd(cmd);
 }
 
-/**
- * transport_put_cmd - release a reference to a command
- * @cmd:       command to release
- *
- * This routine releases our reference to the command and frees it if possible.
- */
-static int transport_put_cmd(struct se_cmd *cmd)
-{
-        transport_free_pages(cmd);
-        return transport_release_cmd(cmd);
-}
-
 void *transport_kmap_data_sg(struct se_cmd *cmd)
 {
         struct scatterlist *sg = cmd->t_data_sg;
@@ -2452,14 +2433,13 @@ static void transport_write_pending_qf(struct se_cmd *cmd)
 
 int transport_generic_free_cmd(struct se_cmd *cmd, int wait_for_tasks)
 {
-        unsigned long flags;
         int ret = 0;
 
         if (!(cmd->se_cmd_flags & SCF_SE_LUN_CMD)) {
                 if (wait_for_tasks && (cmd->se_cmd_flags & SCF_SCSI_TMR_CDB))
-                         transport_wait_for_tasks(cmd);
+                        transport_wait_for_tasks(cmd);
 
-                ret = transport_release_cmd(cmd);
+                ret = transport_put_cmd(cmd);
         } else {
                 if (wait_for_tasks)
                         transport_wait_for_tasks(cmd);
@@ -2468,11 +2448,8 @@ int transport_generic_free_cmd(struct se_cmd *cmd, int wait_for_tasks)
                  * has already added se_cmd to state_list, but fabric has
                  * failed command before I/O submission.
                  */
-                if (cmd->state_active) {
-                        spin_lock_irqsave(&cmd->t_state_lock, flags);
+                if (cmd->state_active)
                         target_remove_from_state_list(cmd);
-                        spin_unlock_irqrestore(&cmd->t_state_lock, flags);
-                }
 
                 if (cmd->se_lun)
                         transport_lun_remove_cmd(cmd);
@@ -2517,6 +2494,16 @@ out:
 }
 EXPORT_SYMBOL(target_get_sess_cmd);
 
+static void target_free_cmd_mem(struct se_cmd *cmd)
+{
+        transport_free_pages(cmd);
+
+        if (cmd->se_cmd_flags & SCF_SCSI_TMR_CDB)
+                core_tmr_release_req(cmd->se_tmr_req);
+        if (cmd->t_task_cdb != cmd->__t_task_cdb)
+                kfree(cmd->t_task_cdb);
+}
+
 static void target_release_cmd_kref(struct kref *kref)
 {
         struct se_cmd *se_cmd = container_of(kref, struct se_cmd, cmd_kref);
@@ -2526,17 +2513,20 @@ static void target_release_cmd_kref(struct kref *kref)
         spin_lock_irqsave(&se_sess->sess_cmd_lock, flags);
         if (list_empty(&se_cmd->se_cmd_list)) {
                 spin_unlock_irqrestore(&se_sess->sess_cmd_lock, flags);
+                target_free_cmd_mem(se_cmd);
                 se_cmd->se_tfo->release_cmd(se_cmd);
                 return;
         }
         if (se_sess->sess_tearing_down && se_cmd->cmd_wait_set) {
                 spin_unlock_irqrestore(&se_sess->sess_cmd_lock, flags);
+                target_free_cmd_mem(se_cmd);
                 complete(&se_cmd->cmd_wait_comp);
                 return;
         }
         list_del(&se_cmd->se_cmd_list);
         spin_unlock_irqrestore(&se_sess->sess_cmd_lock, flags);
 
+        target_free_cmd_mem(se_cmd);
         se_cmd->se_tfo->release_cmd(se_cmd);
 }
 
@@ -2548,6 +2538,7 @@ int target_put_sess_cmd(struct se_cmd *se_cmd)
         struct se_session *se_sess = se_cmd->se_sess;
 
         if (!se_sess) {
+                target_free_cmd_mem(se_cmd);
                 se_cmd->se_tfo->release_cmd(se_cmd);
                 return 1;
         }