On Wed, Oct 22, 2025 at 04:01:04PM +0800, Li Lingfeng wrote:
Hi,
在 2025/10/14 11:03, Sasha Levin 写道:
From: Zheng Qixing zhengqixing@huawei.com
[ Upstream commit 8d33a030c566e1f105cd5bf27f37940b6367f3be ]
There is a race condition between dm device suspend and table load that can lead to null pointer dereference. The issue occurs when suspend is invoked before table load completes:
BUG: kernel NULL pointer dereference, address: 0000000000000054 Oops: 0000 [#1] PREEMPT SMP PTI CPU: 6 PID: 6798 Comm: dmsetup Not tainted 6.6.0-g7e52f5f0ca9b #62 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.1-2.fc37 04/01/2014 RIP: 0010:blk_mq_wait_quiesce_done+0x0/0x50 Call Trace:
<TASK> blk_mq_quiesce_queue+0x2c/0x50 dm_stop_queue+0xd/0x20 __dm_suspend+0x130/0x330 dm_suspend+0x11a/0x180 dev_suspend+0x27e/0x560 ctl_ioctl+0x4cf/0x850 dm_ctl_ioctl+0xd/0x20 vfs_ioctl+0x1d/0x50 __se_sys_ioctl+0x9b/0xc0 __x64_sys_ioctl+0x19/0x30 x64_sys_call+0x2c4a/0x4620 do_syscall_64+0x9e/0x1b0
The issue can be triggered as below:
T1 T2 dm_suspend table_load __dm_suspend dm_setup_md_queue dm_mq_init_request_queue blk_mq_init_allocated_queue => q->mq_ops = set->ops; (1) dm_stop_queue / dm_wait_for_completion => q->tag_set NULL pointer! (2) => q->tag_set = set; (3)
Fix this by checking if a valid table (map) exists before performing request-based suspend and waiting for target I/O. When map is NULL, skip these table-dependent suspend steps.
Even when map is NULL, no I/O can reach any target because there is no table loaded; I/O submitted in this state will fail early in the DM layer. Skipping the table-dependent suspend logic in this case is safe and avoids NULL pointer dereferences.
Fixes: c4576aed8d85 ("dm: fix request-based dm's use of dm_wait_for_completion") Cc: stable@vger.kernel.org Signed-off-by: Zheng Qixing zhengqixing@huawei.com Signed-off-by: Mikulas Patocka mpatocka@redhat.com [ omitted DMF_QUEUE_STOPPED flag setting and braces absent in 5.15 ] Signed-off-by: Sasha Levin sashal@kernel.org
drivers/md/dm.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/drivers/md/dm.c b/drivers/md/dm.c index 0868358a7a8d2..b51281ce15d4c 100644 --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -2457,7 +2457,7 @@ static int __dm_suspend(struct mapped_device *md, struct dm_table *map, { bool do_lockfs = suspend_flags & DM_SUSPEND_LOCKFS_FLAG; bool noflush = suspend_flags & DM_SUSPEND_NOFLUSH_FLAG;
- int r;
- int r = 0; lockdep_assert_held(&md->suspend_lock);
@@ -2509,7 +2509,7 @@ static int __dm_suspend(struct mapped_device *md, struct dm_table *map, * Stop md->queue before flushing md->wq in case request-based * dm defers requests to md->wq from md->queue. */
- if (dm_request_based(md))
- if (map && dm_request_based(md)) dm_stop_queue(md->queue);
It seems that before commit 80bd4a7aab4c ("blk-mq: move the srcu_struct used for quiescing to the tagset") was merged, blk_mq_wait_quiesce_done() would not attempt to access q->tag_set, so in dm_stop_queue() this kind of race condition would not cause a null pointer dereference. The change may not be necessary for 5.10, but adding it doesn’t appear to cause any issues either.
flush_workqueue(md->wq); @@ -2519,7 +2519,8 @@ static int __dm_suspend(struct mapped_device *md, struct dm_table *map, * We call dm_wait_for_completion to wait for all existing requests * to finish. */
- r = dm_wait_for_completion(md, task_state);
- if (map)
r = dm_wait_for_completion(md, task_state);The fix tag c4576aed8d85 ("dm: fix request-based dm's use of dm_wait_for_completion") seems to correspond to the modification of dm_wait_for_completion().
if (!r) set_bit(dmf_suspended_flag, &md->flags);
Perhaps adding another fix tag would be more appropriate?
Those tags come directly from the original commit.