Re: [f2fs-dev] [PATCH v4] f2fs: drop pending discard commands before reserving device alias

[Chao Yu]

On 9/4/2026 12:10 AM, Daeho Jeong wrote:
> From: Daeho Jeong <daehojeong@xxxxxxxxxx>
>
> When reserving a device alias via f2fs_ioc_reserve_dev_alias(),
> f2fs_reserve_device_alias() bulk-marks all blocks in the target device
> range as valid in SIT.
>
> However, if the device was previously in the released state, stale
> pending discard commands covering that range may still exist in dcc->root.
> When f2fs_issue_discard_thread later processes those commands,
> __check_sit_bitmap() detects valid blocks in the discard range and
> triggers a kernel BUG().
>
> To fix this:
> 1. Introduce f2fs_drop_discard_cmd_range() to traverse the discard rbtree,
>     drop all pending D_PREP discard commands in the range,
>     and wait for any in-flight discard bios under dcc->cmd_lock.
> 2. Call f2fs_drop_discard_cmd_range() in f2fs_ioc_reserve_dev_alias()
>     before f2fs_reserve_device_alias().
>
> Reported-by: Wenjie Qi <qiwenjie@xxxxxxxxxx>
> Fixes: eae3faf210bd ("f2fs: support dynamic reserve/release for device aliasing")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Daeho Jeong <daehojeong@xxxxxxxxxx>

Reviewed-by: Chao Yu <chao@xxxxxxxxxx>

Thanks,