Re: [blktests] zbd/012: Test requeuing of zoned writes and queue freezing

[Damien Le Moal <dlemoal@kernel.org>]

On 11/28/24 02:10, Bart Van Assche wrote:
> On 11/26/24 10:21 PM, Christoph Hellwig wrote:
>> On Tue, Nov 26, 2024 at 10:16:18PM -0800, Christoph Hellwig wrote:
>>> Did you trace where the bio_wouldblock_error is coming from?  Probably
>>> a failing request allocation?  Can we call the guts of blk_zone_plug_bio
>>> after allocating the request to avoid this?
>>
>> The easier option might be to simply to "unprepare" the bio
>> (i.e. undo the append op rewrite and sector adjustment), decrement
>> wp_offset and retun.  Given that no one else could issue I/O
>> while we were trying to allocate the bio this should work just fine.
> 
> Yet another possibility is to move the code that updates
> zwplug->wp_offset from blk_zone_plug_bio() into 
> blk_zone_write_plug_init_request(). With this change the 
> zwplug->wp_offset update won't have to be undone in any case since it
> happens after the all code in blk_mq_submit_bio() that can potentially
> fail.

We could for mq devices, but given that blk_zone_write_plug_init_request() is
not used for BIO devices (dm), we would still need to update the wp early. And
DM may have different failure patterns for REQ_NOWAIT BIOs, so it seems simpler
and more solid to punt the BIO to the BIO work and ignore the REQ_NOWAIT flag there.


-- 
Damien Le Moal
Western Digital Research