Re: [f2fs-dev] [PATCH v2] f2fs: invalidate block device page cache on umount

[Chao Yu via Linux-f2fs-devel <linux-f2fs-devel@lists.sourceforge.net>]

On 3/24/26 17:47, Yongpeng Yang wrote:
> From: Yongpeng Yang <yangyongpeng@xiaomi.com>
> 
> Neither F2FS nor VFS invalidates the block device page cache, which
> results in reading stale metadata. An example scenario is shown below:
> 
> Terminal A                  Terminal B
> mount /dev/vdb /mnt/f2fs
> touch mx // ino = 4
> sync
> dump.f2fs -i 4 /dev/vdb// block on "[Y/N]"
>                             touch mx2 // ino = 5
>                             sync
>                             umount /mnt/f2fs
>                             dump.f2fs -i 5 /dev/vdb // block addr is 0
> 
> After umount, the block device page cache is not purged, causing
> `dump.f2fs -i 5 /dev/vdb` to read stale metadata and see inode 5 with
> block address 0.
> 
> Btrfs has encountered a similar issue before, the solution there was to
> call sync_blockdev() and invalidate_bdev() when the device is closed:
> 
> mail-archive.com/linux-btrfs@vger.kernel.org/msg54188.html
> 
> For the root user, the f2fs kernel calls sync_blockdev() on umount to
> flush all cached data to disk, and f2fs-tools can release the page cache
> by issuing ioctl(fd, BLKFLSBUF) when accessing the device. However,
> non-root users are not permitted to drop the page cache, and may still
> observe stale data.
> 
> This patch calls sync_blockdev() and invalidate_bdev() during umount to
> invalidate the block device page cache, thereby preventing stale
> metadata from being read.
> 
> Note that this may result in an extra sync_blockdev() call on the first
> device, in both f2fs_put_super() and kill_block_super(). The second call
> do nothing, as there are no dirty pages left to flush. It ensures that
> non-root users do not observe stale data.
> 
> Signed-off-by: Yongpeng Yang <yangyongpeng@xiaomi.com>

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

Thanks,


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