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Commit7b29518728("block: Do not remove zone write plugs still in use") modified disk_should_remove_zone_wplug() to add a check on the reference count of a zone write plug to prevent removing zone write plugs from a disk hash table when the plugs are still being referenced by BIOs or requests in-flight. However, this check does not take into account that a BIO completion may happen right after its submission by a zone write plug BIO work, and before the zone write plug BIO work releases the zone write plug reference count. This situation leads to disk_should_remove_zone_wplug() returning false as in this case the zone write plug reference count is at least equal to 3. If the BIO that completes in such manner transitioned the zone to the FULL condition, the zone write plug for the FULL zone will remain in the disk hash table. Furthermore, relying on a particular value of a zone write plug reference count to set the BLK_ZONE_WPLUG_UNHASHED flag is fragile as reading the atomic reference count and doing a comparison with some value is not overall atomic at all. Address these issues by reworking the reference counting of zone write plugs so that removing plugs from a disk hash table can be done directly from disk_put_zone_wplug() when the last reference on a plug is dropped. To do so, replace the function disk_remove_zone_wplug() with disk_mark_zone_wplug_dead(). This new function sets the zone write plug flag BLK_ZONE_WPLUG_DEAD (which replaces BLK_ZONE_WPLUG_UNHASHED) and drops the initial reference on the zone write plug taken when the plug was added to the disk hash table. This function is called either for zones that are empty or full, or directly in the case of a forced plug removal (e.g. when the disk hash table is being destroyed on disk removal). With this change, disk_should_remove_zone_wplug() is also removed. disk_put_zone_wplug() is modified to call the function disk_free_zone_wplug() to remove a zone write plug from a disk hash table and free the plug structure (with a call_rcu()), when the last reference on a zone write plug is dropped. disk_free_zone_wplug() always checks that the BLK_ZONE_WPLUG_DEAD flag is set. In order to avoid having multiple zone write plugs for the same zone in the disk hash table, disk_get_and_lock_zone_wplug() checked for the BLK_ZONE_WPLUG_UNHASHED flag. This check is removed and a check for the new BLK_ZONE_WPLUG_DEAD flag is added to blk_zone_wplug_handle_write(). With this change, we continue preventing adding multiple zone write plugs for the same zone and at the same time re-inforce checks on the user behavior by failing new incoming write BIOs targeting a zone that is marked as dead. This case can happen only if the user erroneously issues write BIOs to zones that are full, or to zones that are currently being reset or finished. Fixes:7b29518728("block: Do not remove zone write plugs still in use") Cc: stable@vger.kernel.org Signed-off-by: Damien Le Moal <dlemoal@kernel.org> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
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