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

Hannes Reinecke
2025-01-13T07:25:30Z

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@lst.de>
> Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
> ---
> block/blk-sysfs.c | 18 ++++++++++--------
> 1 file changed, 10 insertions(+), 8 deletions(-)
>
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
--
Dr. Hannes Reinecke Kernel Storage Architect
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