Re: [PATCH v3] mmc: core: don't set limits.discard_granularity as 0

[Vicente Bergas]

On Thu, Oct 1, 2020 at 11:07 AM Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote:
>
> On 1/10/20 11:38 am, Vicente Bergas wrote:
> > On Thu, Oct 1, 2020 at 9:18 AM Coly Li <colyli@xxxxxxx> wrote:
> >>
> >> In mmc_queue_setup_discard() the mmc driver queue's discard_granularity
> >> might be set as 0 (when card->pref_erase > max_discard) while the mmc
> >> device still declares to support discard operation. This is buggy and
> >> triggered the following kernel warning message,
> >>
> >> WARNING: CPU: 0 PID: 135 at __blkdev_issue_discard+0x200/0x294
> >> CPU: 0 PID: 135 Comm: f2fs_discard-17 Not tainted 5.9.0-rc6 #1
> >> Hardware name: Google Kevin (DT)
> >> pstate: 00000005 (nzcv daif -PAN -UAO BTYPE=--)
> >> pc : __blkdev_issue_discard+0x200/0x294
> >> lr : __blkdev_issue_discard+0x54/0x294
> >> sp : ffff800011dd3b10
> >> x29: ffff800011dd3b10 x28: 0000000000000000 x27: ffff800011dd3cc4 x26: ffff800011dd3e18 x25: 000000000004e69b x24: 0000000000000c40 x23: ffff0000f1deaaf0 x22: ffff0000f2849200 x21: 00000000002734d8 x20: 0000000000000008 x19: 0000000000000000 x18: 0000000000000000 x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000 x14: 0000000000000394 x13: 0000000000000000 x12: 0000000000000000 x11: 0000000000000000 x10: 00000000000008b0 x9 : ffff800011dd3cb0 x8 : 000000000004e69b x7 : 0000000000000000 x6 : ffff0000f1926400 x5 : ffff0000f1940800 x4 : 0000000000000000 x3 : 0000000000000c40 x2 : 0000000000000008 x1 : 00000000002734d8 x0 : 0000000000000000 Call trace:
> >> __blkdev_issue_discard+0x200/0x294
> >> __submit_discard_cmd+0x128/0x374
> >> __issue_discard_cmd_orderly+0x188/0x244
> >> __issue_discard_cmd+0x2e8/0x33c
> >> issue_discard_thread+0xe8/0x2f0
> >> kthread+0x11c/0x120
> >> ret_from_fork+0x10/0x1c
> >> ---[ end trace e4c8023d33dfe77a ]---
> >>
> >> This patch fixes the issue by setting discard_granularity as SECTOR_SIZE
> >> instead of 0 when (card->pref_erase > max_discard) is true. Now no more
> >> complain from __blkdev_issue_discard() for the improper value of discard
> >> granularity.
> >>
> >> This issue is exposed after commit b35fd7422c2f ("block: check queue's
> >> limits.discard_granularity in __blkdev_issue_discard()"), a "Fixes:" tag
> >> is also added for the commit to make sure people won't miss this patch
> >> after applying the change of __blkdev_issue_discard().
> >>
> >> Fixes: e056a1b5b67b ("mmc: queue: let host controllers specify maximum discard timeout")
> >> Fixes: b35fd7422c2f ("block: check queue's limits.discard_granularity in __blkdev_issue_discard()").
> >> Reported-by: Vicente Bergas <vicencb@xxxxxxxxx>
> >
> > Hi Coly, Adrian,
> > would you like me to reply with a tested-by?
> > before testing it: what are the chances of losing data?
>
> Very low I would hope, but that is no reason not to have backups :-)

I do have backup, it is for the hassle of reinstalling the OS and
restoring the backup.
I'll test it later, maybe today.

> > Regards,
> >   Vicente.
> >
> >> Signed-off-by: Coly Li <colyli@xxxxxxx>
> >> Acked-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> >> Cc: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
> >> ---
> >> Changelog,
> >> v3, add Fixes tag for both commits.
> >> v2, change commit id of the Fixes tag.
> >> v1, initial version.
> >>
> >>  drivers/mmc/core/queue.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/mmc/core/queue.c b/drivers/mmc/core/queue.c
> >> index 6c022ef0f84d..350d0cc4ee62 100644
> >> --- a/drivers/mmc/core/queue.c
> >> +++ b/drivers/mmc/core/queue.c
> >> @@ -190,7 +190,7 @@ static void mmc_queue_setup_discard(struct request_queue *q,
> >>         q->limits.discard_granularity = card->pref_erase << 9;
> >>         /* granularity must not be greater than max. discard */

Just out of curiosity, wouldn't it be more performant something like:
q->limits.discard_granularity = minimum(card->pref_erase, max_discard) << 9;
or is just that SECTOR_SIZE is a number guaranteed to work?

> >>         if (card->pref_erase > max_discard)
> >> -               q->limits.discard_granularity = 0;
> >> +               q->limits.discard_granularity = SECTOR_SIZE;
> >>         if (mmc_can_secure_erase_trim(card))
> >>                 blk_queue_flag_set(QUEUE_FLAG_SECERASE, q);
> >>  }
> >> --
> >> 2.26.2
> >>
>