[PATCH 2/2] target: iscsi: fix a race condition when aborting a task

[Maurizio Lombardi <mlombard@redhat.com>]

The iscsit_release_commands_from_conn() function does the following
operations:

1) locks the cmd_lock spinlock
2) Scans the list of commands and sets the CMD_T_FABRIC_STOP flag
3) Releases the cmd_lock spinlock
4) Rescans the list again and clears the i_conn_node link of each command

If an abort task timer is fired between 3) and 4), it will find
the CMD_T_FABRIC_STOP flag set and won't call list_del_init();
therefore it may end up calling __iscsit_free_cmd() with a
non-empty i_conn_node list, thus triggering the warning.

Considering that:

- we expect list_del_init() to be executed by
  iscsit_release_commands_from_conn() when the CMD_T_FABRIC_STOP is set.
- iscsit_aborted_task() is the only function that calls __iscsit_free_cmd()
  directly, while all the other functions call iscsit_free_cmd().
- the warning in __iscsit_free_cmd() is a duplicate (the same warning
  can be found in iscsit_free_cmd().

We can fix the bug by simply removing the warning from __iscsit_free_cmd()

kernel: ------------[ cut here ]------------
kernel: WARNING: CPU: 1 PID: 21173 at drivers/target/iscsi/iscsi_target_util.c:720 __iscsit_free_cmd+0x26e/0x290 [iscsi_target_mod]
...
kernel: CPU: 1 PID: 21173 Comm: kworker/u8:3 Kdump: loaded Not tainted 3.10.0-1062.4.1.el7.x86_64 #1
kernel: Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 09/17/2015
kernel: Workqueue: tmr-user target_tmr_work [target_core_mod]
kernel: Call Trace:
kernel: [<ffffffff91d78ba4>] dump_stack+0x19/0x1b
kernel: [<ffffffff9169a958>] __warn+0xd8/0x100
kernel: [<ffffffff9169aa9d>] warn_slowpath_null+0x1d/0x20
kernel: [<ffffffffc0a6f69e>] __iscsit_free_cmd+0x26e/0x290 [iscsi_target_mod]
kernel: [<ffffffffc0a70bc4>] iscsit_aborted_task+0x64/0x70 [iscsi_target_mod]
kernel: [<ffffffffc0a7830a>] lio_aborted_task+0x2a/0x30 [iscsi_target_mod]
kernel: [<ffffffffc09fa516>] transport_cmd_finish_abort+0x66/0xb0 [target_core_mod]
kernel: [<ffffffffc09f4d92>] core_tmr_abort_task+0x102/0x180 [target_core_mod]
kernel: [<ffffffffc09f7bb2>] target_tmr_work+0x152/0x170 [target_core_mod]
kernel: [<ffffffff916bd1df>] process_one_work+0x17f/0x440
kernel: [<ffffffff916be2f6>] worker_thread+0x126/0x3c0
kernel: [<ffffffff916be1d0>] ? manage_workers.isra.26+0x2a0/0x2a0
kernel: [<ffffffff916c51b1>] kthread+0xd1/0xe0
kernel: [<ffffffff916c50e0>] ? insert_kthread_work+0x40/0x40
kernel: [<ffffffff91d8bd37>] ret_from_fork_nospec_begin+0x21/0x21
kernel: [<ffffffff916c50e0>] ? insert_kthread_work+0x40/0x40
kernel: ---[ end trace ed2119501826ec7a ]---


Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
---
 drivers/target/iscsi/iscsi_target_util.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/target/iscsi/iscsi_target_util.c b/drivers/target/iscsi/iscsi_target_util.c
index 3082f5bde9fa..61233755ece0 100644
--- a/drivers/target/iscsi/iscsi_target_util.c
+++ b/drivers/target/iscsi/iscsi_target_util.c
@@ -741,8 +741,6 @@ void __iscsit_free_cmd(struct iscsi_cmd *cmd, bool check_queues)
 {
 	struct iscsi_conn *conn = cmd->conn;
 
-	WARN_ON(!list_empty(&cmd->i_conn_node));
-
 	if (cmd->data_direction = DMA_TO_DEVICE) {
 		iscsit_stop_dataout_timer(cmd);
 		iscsit_free_r2ts_from_list(cmd);
-- 
2.26.2