[PATCH AUTOSEL 6.19-5.10] dm: remove fake timeout to avoid leak request

[Sasha Levin <sashal@kernel.org>]

From: Ding Hui <dinghui@sangfor.com.cn>

[ Upstream commit f3a9c95a15d2f4466acad5c68faeff79ca5e9f47 ]

Since commit 15f73f5b3e59 ("blk-mq: move failure injection out of
blk_mq_complete_request"), drivers are responsible for calling
blk_should_fake_timeout() at appropriate code paths and opportunities.

However, the dm driver does not implement its own timeout handler and
relies on the timeout handling of its slave devices.

If an io-timeout-fail error is injected to a dm device, the request
will be leaked and never completed, causing tasks to hang indefinitely.

Reproduce:
1. prepare dm which has iscsi slave device
2. inject io-timeout-fail to dm
   echo 1 >/sys/class/block/dm-0/io-timeout-fail
   echo 100 >/sys/kernel/debug/fail_io_timeout/probability
   echo 10 >/sys/kernel/debug/fail_io_timeout/times
3. read/write dm
4. iscsiadm -m node -u

Result: hang task like below
[  862.243768] INFO: task kworker/u514:2:151 blocked for more than 122 seconds.
[  862.244133]       Tainted: G            E       6.19.0-rc1+ #51
[  862.244337] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[  862.244718] task:kworker/u514:2  state:D stack:0     pid:151   tgid:151   ppid:2      task_flags:0x4288060 flags:0x00080000
[  862.245024] Workqueue: iscsi_ctrl_3:1 __iscsi_unbind_session [scsi_transport_iscsi]
[  862.245264] Call Trace:
[  862.245587]  <TASK>
[  862.245814]  __schedule+0x810/0x15c0
[  862.246557]  schedule+0x69/0x180
[  862.246760]  blk_mq_freeze_queue_wait+0xde/0x120
[  862.247688]  elevator_change+0x16d/0x460
[  862.247893]  elevator_set_none+0x87/0xf0
[  862.248798]  blk_unregister_queue+0x12e/0x2a0
[  862.248995]  __del_gendisk+0x231/0x7e0
[  862.250143]  del_gendisk+0x12f/0x1d0
[  862.250339]  sd_remove+0x85/0x130 [sd_mod]
[  862.250650]  device_release_driver_internal+0x36d/0x530
[  862.250849]  bus_remove_device+0x1dd/0x3f0
[  862.251042]  device_del+0x38a/0x930
[  862.252095]  __scsi_remove_device+0x293/0x360
[  862.252291]  scsi_remove_target+0x486/0x760
[  862.252654]  __iscsi_unbind_session+0x18a/0x3e0 [scsi_transport_iscsi]
[  862.252886]  process_one_work+0x633/0xe50
[  862.253101]  worker_thread+0x6df/0xf10
[  862.253647]  kthread+0x36d/0x720
[  862.254533]  ret_from_fork+0x2a6/0x470
[  862.255852]  ret_from_fork_asm+0x1a/0x30
[  862.256037]  </TASK>

Remove the blk_should_fake_timeout() check from dm, as dm has no
native timeout handling and should not attempt to fake timeouts.

Signed-off-by: Ding Hui <dinghui@sangfor.com.cn>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

Good — the current code in this tree still has the buggy
`blk_should_fake_timeout()` check, confirming the fix hasn't been
applied yet.

### 8. SUMMARY

| Criterion | Assessment |
|-----------|------------|
| Fixes a real bug | YES — request leak causing hung tasks |
| Obviously correct | YES — dm shouldn't fake timeouts without a timeout
handler |
| Small and contained | YES — 2 lines removed in 1 file |
| No new features | Correct — removes incorrect behavior |
| Tested | YES — reproduction steps and stack trace provided |
| Risk of regression | Very low — only affects fault injection testing
path |
| Expert review | YES — Christoph Hellwig reviewed, Mikulas Patocka
signed off |
| Applicable to stable | YES — prerequisite commit from 2020, present in
all stable trees |

### CONCLUSION

This is a textbook stable backport candidate: a small, surgical fix for
a real bug (request leak causing indefinite task hangs) in a widely-used
subsystem (device mapper), reviewed by top-tier kernel developers, with
minimal regression risk. The bug has existed since 2020 in all
maintained stable trees. The fix is trivially correct — dm shouldn't
participate in fake timeout injection when it has no timeout handler.

**YES**

 drivers/md/dm-rq.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/md/dm-rq.c b/drivers/md/dm-rq.c
index a6ca92049c10e..5e08546696145 100644
--- a/drivers/md/dm-rq.c
+++ b/drivers/md/dm-rq.c
@@ -278,8 +278,7 @@ static void dm_complete_request(struct request *rq, blk_status_t error)
 	struct dm_rq_target_io *tio = tio_from_request(rq);
 
 	tio->error = error;
-	if (likely(!blk_should_fake_timeout(rq->q)))
-		blk_mq_complete_request(rq);
+	blk_mq_complete_request(rq);
 }
 
 /*
-- 
2.51.0