Patch "md: fix resync softlockup when bitmap size is less than array size" has been added to the 5.15-stable tree

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This is a note to let you know that I've just added the patch titled

    md: fix resync softlockup when bitmap size is less than array size

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     md-fix-resync-softlockup-when-bitmap-size-is-less-th.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 94803023a23b907ef29ed974f604fd73b2fa2c03
Author: Yu Kuai <yukuai3@xxxxxxxxxx>
Date:   Mon Apr 22 14:58:24 2024 +0800

    md: fix resync softlockup when bitmap size is less than array size
    
    [ Upstream commit f0e729af2eb6bee9eb58c4df1087f14ebaefe26b ]
    
    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>
    Link: https://lore.kernel.org/r/20240422065824.2516-1-yukuai1@xxxxxxxxxxxxxxx
    Signed-off-by: Song Liu <song@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c
index 49c46f3aea573..b26e22dd9ba2e 100644
--- a/drivers/md/md-bitmap.c
+++ b/drivers/md/md-bitmap.c
@@ -1355,7 +1355,7 @@ __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) {
@@ -1364,6 +1364,7 @@ __acquires(bitmap->lock)
 		 * 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);
@@ -1372,8 +1373,7 @@ __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)




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