Re: [PATCH] md/bitmap: clear BITMAP_WRITE_ERROR bit after reading it from sb

[Shaohua Li <shli@kernel.org>]

On Fri, Oct 13, 2017 at 06:36:31PM +0800, Hou Tao wrote:
> For a RAID1 device using a file-based bitmap, if a bitmap write error
> occurs and the later writes succeed, it's possible both BITMAP_STALE
> and BITMAP_WRITE_ERROR bit will be written to the bitmap super block,
> and the BITMAP_WRITE_ERROR bit in sb->flags will make bitmap_create()
> to fail.

Why don't clear the bit in the 'latter succeeded write'?
 
> So clear it to protect against the write failure-success case.
> 
> Signed-off-by: Hou Tao <houtao1@huawei.com>
> ---
>  drivers/md/bitmap.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
> index d212163..97c423a 100644
> --- a/drivers/md/bitmap.c
> +++ b/drivers/md/bitmap.c
> @@ -688,8 +688,13 @@ static int bitmap_read_sb(struct bitmap *bitmap)
>  		}
>  	}
>  
> -	/* assign fields using values from superblock */
> -	bitmap->flags |= le32_to_cpu(sb->state);
> +	/*
> +	 * assign fields using values from superblock
> +	 * clear BITMAP_WRITE_ERROR bit to protect against the case that
> +	 * a bitmap write error had occurred and the later writes had
> +	 * succeeded.
> +	 */
> +	bitmap->flags |= (le32_to_cpu(sb->state) & ~BIT(BITMAP_WRITE_ERROR));
>  	if (le32_to_cpu(sb->version) == BITMAP_MAJOR_HOSTENDIAN)
>  		set_bit(BITMAP_HOSTENDIAN, &bitmap->flags);
>  	bitmap->events_cleared = le64_to_cpu(sb->events_cleared);
> -- 
> 2.5.0
>