On 2025/03/26 11:00, Benjamin Marzinski wrote: > On Wed, Mar 26, 2025 at 08:55:48AM -0400, Damien Le Moal wrote: >> On 2025/03/21 13:52, Benjamin Marzinski wrote: >>> On Fri, Mar 21, 2025 at 08:18:16AM +0100, Christoph Hellwig wrote: >>>> Add support for zoned device by passing through report_zoned to the >>>> underlying read device. >>>> >>>> This is required to make enable xfstests xfs/311 on zoned devices. >>> >>> On suspend, delay_presuspend() stops delaying and it doesn't guarantee >>> that new bios coming in will always be submitted after the delayed bios >>> it is flushing. That can mess things up for zoned devices. I didn't >>> check if that matters for the specific test. Setting >>> >>> ti->emulate_zone_append = true; >>> >>> would enforce write ordering, at the expense of adding a whole other >>> layer of delays to zoned dm-delay devices. Since this isn't really >>> useful outside of testing, I think that could be acceptable if necessary >>> (it would require us to support table reloads of zoned devices with >>> emulated zone append, since tests often want to change the delay). >>> However it would probably be better to see if we can just make dm-delay >>> preserve write ordering during a suspend. >> >> delay_presuspend() calls flush_delayed_bios() with flush_all == true. So all >> BIOs will be flushed in the order they are queued in the delay list, which as >> far as I can tell is the order in which the user of dm-delay issued the >> BIOs. So >> for writes, the order is preserved as far as I can tell. > > delay_presuspend() is called before we set the DMF_BLOCK_IO_FOR_SUSPEND > bit, which will stop incoming bio from getting mapped, and also before > lock_fs() is called. This means it's common for new bios to continue to > come into delay_map(), while delay_presuspend() is running. The moment > delay_presuspend() sets dc->may_delay = false, those new bios will stop > getting queued by delay_bio(). They will get remapped immeditately to > the underlying device. flush_delayed_bios() doesn't even get called > until after dc->may_delay is set to false, and if there are a lot of > bios on the delayed_bios list, flush_delayed_bios() will schedule. So, > it's actually very common for new incoming bios to get passed to > underlying device before all the bios on the dc->delayed_bios list do. > > Solving this without grabbing the dc->process_bios_lock mutex for every > bio sent to dm-delay probably involves keeping the incoming bios going > to dc->delayed_bios during suspend, at least until we can guarantee that > it's empty and no bios are being flushed.
OK. Understood. Thank you for the explanation. And the above sounds like a rather simple solution, which does not even needs to be zone specific. I also think that this is orthogonal to Christoph patch and we can fix the suspend issue on top of Christoph's patch. This is a very niche issue anyway for the main target use case which is fstests, since fstests does not suspend/resume the dm-delay device as far as I know. > > -Ben > >> >> -- >> Damien Le Moal >> Western Digital Research > -- Damien Le Moal Western Digital Research
