Re: [PATCH -next] md: fix resync softlockup when bitmap size is less than array size

[Yu Kuai]

+CC Nigel

Sorry I forgot that.

在 2024/04/22 14:58, Yu Kuai 写道:
> From: Yu Kuai <yukuai3@xxxxxxxxxx>
>
> Is is reported that for dm-raid10, lvextend + lvchange --syncaction will
> trigger following softlockup:
>
> kernel:watchdog: BUG: soft lockup - CPU#3 stuck for 26s! [mdX_resync:6976]
> CPU: 7 PID: 3588 Comm: mdX_resync Kdump: loaded Not tainted 6.9.0-rc4-next-20240419 #1
> RIP: 0010:_raw_spin_unlock_irq+0x13/0x30
> Call Trace:
>   <TASK>
>   md_bitmap_start_sync+0x6b/0xf0
>   raid10_sync_request+0x25c/0x1b40 [raid10]
>   md_do_sync+0x64b/0x1020
>   md_thread+0xa7/0x170
>   kthread+0xcf/0x100
>   ret_from_fork+0x30/0x50
>   ret_from_fork_asm+0x1a/0x30
>
> And the detailed process is as follows:
>
> md_do_sync
>   j = mddev->resync_min
>   while (j < max_sectors)
>    sectors = raid10_sync_request(mddev, j, &skipped)
>     if (!md_bitmap_start_sync(..., &sync_blocks))
>      // md_bitmap_start_sync set sync_blocks to 0
>      return sync_blocks + sectors_skippe;
>    // sectors = 0;
>    j += sectors;
>    // j never change
>
> Root cause is that commit 301867b1c168 ("md/raid10: check
> slab-out-of-bounds in md_bitmap_get_counter") return early from
> md_bitmap_get_counter(), without setting returned blocks.
>
> Fix this problem by always set returned blocks from
> md_bitmap_get_counter"(), as it used to be.
>
> Noted that this patch just fix the softlockup problem in kernel, the
> case that bitmap size doesn't match array size still need to be fixed.
>
> Fixes: 301867b1c168 ("md/raid10: check slab-out-of-bounds in md_bitmap_get_counter")
> Reported-and-tested-by: Nigel Croxon <ncroxon@xxxxxxxxxx>
> Closes: https://lore.kernel.org/all/71ba5272-ab07-43ba-8232-d2da642acb4e@xxxxxxxxxx/
> Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
> ---
>   drivers/md/md-bitmap.c | 7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c
> index 059afc24c08b..f5b66d52cbe3 100644
> --- a/drivers/md/md-bitmap.c
> +++ b/drivers/md/md-bitmap.c
> @@ -1424,15 +1424,17 @@ __acquires(bitmap->lock)
>   	sector_t chunk = offset >> bitmap->chunkshift;
>   	unsigned long page = chunk >> PAGE_COUNTER_SHIFT;
>   	unsigned long pageoff = (chunk & PAGE_COUNTER_MASK) << COUNTER_BYTE_SHIFT;
> -	sector_t csize;
> +	sector_t csize = ((sector_t)1) << bitmap->chunkshift;
>   	int err;
>   
> +
>   	if (page >= bitmap->pages) {
>   		/*
>   		 * This can happen if bitmap_start_sync goes beyond
>   		 * End-of-device while looking for a whole page or
>   		 * user set a huge number to sysfs bitmap_set_bits.
>   		 */
> +		*blocks = csize - (offset & (csize - 1));
>   		return NULL;
>   	}
>   	err = md_bitmap_checkpage(bitmap, page, create, 0);
> @@ -1441,8 +1443,7 @@ __acquires(bitmap->lock)
>   	    bitmap->bp[page].map == NULL)
>   		csize = ((sector_t)1) << (bitmap->chunkshift +
>   					  PAGE_COUNTER_SHIFT);
> -	else
> -		csize = ((sector_t)1) << bitmap->chunkshift;
> +
>   	*blocks = csize - (offset & (csize - 1));
>   
>   	if (err < 0)