Re: [PATCH 05/10] block: fix queue freeze vs limits lock order in sysfs store methods

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On 1/8/25 10:25, Christoph Hellwig wrote:
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@xxxxxx>
Reviewed-by: Nilay Shroff <nilay@xxxxxxxxxxxxx>
---
  block/blk-sysfs.c | 18 ++++++++++--------
  1 file changed, 10 insertions(+), 8 deletions(-)

Reviewed-by: Hannes Reinecke <hare@xxxxxxx>

Cheers,

Hannes
--
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@xxxxxxx                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich




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