On 8/16/24 11:23, Shin'ichiro Kawasaki wrote:
> As the helper function f2fs_bdev_support_discard() shows, f2fs checks if
> the target block devices support discard by calling
> bdev_max_discard_sectors() and bdev_is_zoned(). This check works good
s/good/well
> for most cases, but it does not work for conventional zones on zoned
> block devices. F2fs assumes that zoned block devices support discard,
> and calls __submit_discard_cmd(). When __submit_discard_cmd() is called
> for sequential write required zones, it works fine since
> __submit_discard_cmd() issues zone reset commands instead of discard
> commands. However, when __submit_discard_cmd() is called for
> conventional zones, __blkdev_issue_discard() is called even when the
> devices do not support discard.
>
> The inappropriate __blkdev_issue_discard() call was not a problem before
> the commit 30f1e7241422 ("block: move discard checks into the ioctl
> handler") because __blkdev_issue_discard() checked if the target devices
> support discard or not. If not, it returned EOPNOTSUPP. After the
> commit, __blkdev_issue_discard() no longer checks it and always returns
> zero and sets NULL to the give bio pointer. This NULL pointer triggers
> f2fs_bug_on() in __submit_discard_cmd(). The BUG is recreated with the
> commands below at the umount step, where /dev/nullb0 is a zoned null_blk
> with 5GB total size, 128MB zone size and 10 conventional zones.
>
> $ mkfs.f2fs -f -m /dev/nullb0
> $ mount /dev/nullb0 /mnt
> $ for ((i=0;i<5;i++)); do dd if=/dev/zero of=/mnt/test bs=65536 count=1600
> conv=fsync; done
> $ umount /mnt
>
> To fix the BUG, avoid the inappropriate __blkdev_issue_discard() call.
> When discard is requested for conventional zones, check if the device
> supports discard or not. If not, return EOPNOTSUPP.
>
> Fixes: 30f1e7241422 ("block: move discard checks into the ioctl handler")
> Cc: [email protected]
> Signed-off-by: Shin'ichiro Kawasaki <[email protected]>
> ---
> fs/f2fs/segment.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 78c3198a6308..e10bf3c4eed5 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -1281,6 +1281,8 @@ static int __submit_discard_cmd(struct f2fs_sb_info
> *sbi,
> __submit_zone_reset_cmd(sbi, dc, flag,
> wait_list, issued);
> return 0;
> + } else if (!bdev_max_discard_sectors(bdev)) {
> + return -EOPNOTSUPP;
> }
You do not need the else here. And I suggest adding a comment as well:
/*
* Issue discard for conventional zones only if the
* device supports discard.
*/
if (!bdev_max_discard_sectors(bdev))
return -EOPNOTSUPP;
With that:
Reviewed-by: Damien Le Moal <[email protected]>
> }
> #endif
--
Damien Le Moal
Western Digital Research
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