On 11/18/24 6:57 PM, Damien Le Moal wrote:
On 11/19/24 9:27 AM, Bart Van Assche wrote:
If the queue is filled with unaligned writes then the following
deadlock occurs:
Call Trace:
<TASK>
__schedule+0x8cc/0x2190
schedule+0xdd/0x2b0
blk_queue_enter+0x2ce/0x4f0
blk_mq_alloc_request+0x303/0x810
scsi_execute_cmd+0x3f4/0x7b0
sd_zbc_do_report_zones+0x19e/0x4c0
sd_zbc_report_zones+0x304/0x920
disk_zone_wplug_handle_error+0x237/0x920
disk_zone_wplugs_work+0x17e/0x430
process_one_work+0xdd0/0x1490
worker_thread+0x5eb/0x1010
kthread+0x2e5/0x3b0
ret_from_fork+0x3a/0x80
</TASK>
Fix this deadlock by removing the disk->fops->report_zones() call and by
deriving the write pointer information from successfully completed zoned
writes.
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
Doesn't this need a Fixes tag and CC stable, and come earlier in the series (or
sent separately) ?
I will add Fixes: and Cc: stable tags.
I'm not sure how to move this patch earlier since it depends on the
previous patch in this series ("blk-zoned: Only handle errors after
pending zoned writes have completed"). Without that patch, it is not
safe to use zwplug->wp_offset_compl in the error handler.
Overall, this patch seems wrong anyway as zone reset and zone finish may be
done between 2 writes, failing the next one but the recovery done here will use
the previous succeful write end position as the wp, which is NOT correct as
reset or finish changed that...
I will add support for the zone reset and zone finish commands in this
patch.
And we also have the possibility of torn writes
(partial writes) with SAS SMR drives. So I really think that you cannot avoid
doing a report zone to recover errors.
Thanks for having brought this up. This is something I was not aware of.
disk_zone_wplug_handle_error() submits a new request to retrieve zone
information while handling an error triggered by other requests. This
can easily lead to a deadlock as the above call trace shows. How about
introducing a queue flag for the "report zones" approach in
disk_zone_wplug_handle_error() such that the "report zones" approach is
only used for SAS SMR drives?
Thanks,
Bart.
