[PATCH 5/8] block: fix queue freeze vs limits lock order in sysfs store methods

Christoph Hellwig
2025-01-07T06:31:41Z

queue_attr_store() always freezes a device queue before calling the
attribute store operation. For attributes that control queue limits, the
store operation will also lock the queue limits with a call to
queue_limits_start_update(). However, some drivers (e.g. SCSI sd) may
need to issue commands to a device to obtain limit values from the
hardware with the queue limits locked. This creates a potential ABBA
deadlock situation if a user attempts to modify a limit (thus freezing
the device queue) while the device driver starts a revalidation of the
device queue limits.

Avoid such deadlock by not freezing the queue before calling the
->store_limit() method in struct queue_sysfs_entry and instead use the
queue_limits_commit_update_frozen helper to freeze the queue after taking
the limits lock.

(commit log adapted from a similar patch from Damien Le Moal)

Fixes: ff956a3be95b ("block: use queue_limits_commit_update in queue_discard_max_store")
Fixes: 0327ca9d53bf ("block: use queue_limits_commit_update in queue_max_sectors_store")
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
block/blk-sysfs.c | 18 ++++++++++--------
1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 8d69315e986d..3bac27fcd635 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -687,22 +687,24 @@ queue_attr_store(struct kobject *kobj, struct attribute *attr,
if (entry->load_module)
entry->load_module(disk, page, length);

- mutex_lock(&q->sysfs_lock);
- blk_mq_freeze_queue(q);
if (entry->store_limit) {
struct queue_limits lim = queue_limits_start_update(q);

res = entry->store_limit(disk, page, length, &lim);
if (res < 0) {
queue_limits_cancel_update(q);
- } else {
- res = queue_limits_commit_update(q, &lim);
- if (!res)
- res = length;
+ return res;
}
- } else {
- res = entry->store(disk, page, length);
+
+ res = queue_limits_commit_update_frozen(q, &lim);
+ if (res)
+ return res;
+ return length;
}
+
+ mutex_lock(&q->sysfs_lock);
+ blk_mq_freeze_queue(q);
+ res = entry->store(disk, page, length);
blk_mq_unfreeze_queue(q);
mutex_unlock(&q->sysfs_lock);
return res;
--
2.45.2