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

[Song Liu]

On Mon, Apr 22, 2024 at 12:07 AM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:
>
> 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>

Applied to md-6.10. Thanks!

Song