Re: [f2fs-dev] [PATCH v2] f2fs: check discard support for conventional zones

[Chao Yu <chao@kernel.org>]

On 2024/8/16 12:07, 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 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. It always returns
> zero and sets NULL to the given 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: stable@vger.kernel.org
> Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
> Reviewed-by: Damien Le Moal <dlemoal@kernel.org>

Reviewed-by: Chao Yu <chao@kernel.org>

Thanks,


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