Re: [PATCH v7 09/16] block: serialize zone revalidation

On 9/8/26 10:57 AM, Damien Le Moal wrote:

The zone related fields of struct gendisk can be modified by
blk_revalidate_disk_zones() either on the first scan of the disk, or
during user triggered scans or device revalidation, if some
characteristics of the disk has changed (e.g. the disk capacity). Changes
to these fields are always done with the disk request queue frozen so that
BIO processing does not see any inconsistent state of the zones. This
implies a contract that reading these zone related fields must always be
done while holding a usage count on the request queue of the disk.

However, increasing the usage count of the disk request queue cannot be
done from the context of blk_revalidate_disk_zones() itself, as that would
prevent freezing the disk queue and result in a deadlock. This prevents
blk_revalidate_disk_zones() from consulting the zone related fields of
struct gendisk to detect, for instance, a change in the number of zones of
the disk. For such case, we want to detect the change, take appropriate
measures and revalidate exclusively revalidate the zones to avoid
concurrent revalidation calls to see the same change while corrections are
already on-going.

A simple solution to avoid this issue is to introduce a mutex to serialize
calls to blk_revalidate_disk_zones() and ensure only a single context at a
time can modify the zone related fields of a gendisk. In preparation for
handling disk capacity revalidation in blk_revalidate_disk_zones(), do so
with the mutex zone_revalidate_mutex. This mutex is initialized in
disk_init_zone_resources(), destroyed in disk_release_zone_resources() and
taken and released only in blk_revalidate_disk_zones() to serialize the
execution of this function.

Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
---
  block/blk-zoned.c      | 17 +++++++++++++++--
  include/linux/blkdev.h |  9 ++++++---
  2 files changed, 21 insertions(+), 5 deletions(-)

Reviewed-by: Hannes Reinecke <hare@kernel.org>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@suse.de                                +49 911 74053 688
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