Patch "ext4: avoid allocating blocks from corrupted group in ext4_mb_try_best_found()" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

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

    ext4: avoid allocating blocks from corrupted group in ext4_mb_try_best_found()

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:
     ext4-avoid-allocating-blocks-from-corrupted-group-in.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 901e97242c26729e7e8e49fa9b1089c10fafbced
Author: Baokun Li <libaokun1@xxxxxxxxxx>
Date:   Thu Jan 4 22:20:38 2024 +0800

    ext4: avoid allocating blocks from corrupted group in ext4_mb_try_best_found()
    
    [ Upstream commit 4530b3660d396a646aad91a787b6ab37cf604b53 ]
    
    Determine if the group block bitmap is corrupted before using ac_b_ex in
    ext4_mb_try_best_found() to avoid allocating blocks from a group with a
    corrupted block bitmap in the following concurrency and making the
    situation worse.
    
    ext4_mb_regular_allocator
      ext4_lock_group(sb, group)
      ext4_mb_good_group
       // check if the group bbitmap is corrupted
      ext4_mb_complex_scan_group
       // Scan group gets ac_b_ex but doesn't use it
      ext4_unlock_group(sb, group)
                               ext4_mark_group_bitmap_corrupted(group)
                               // The block bitmap was corrupted during
                               // the group unlock gap.
      ext4_mb_try_best_found
        ext4_lock_group(ac->ac_sb, group)
        ext4_mb_use_best_found
          mb_mark_used
          // Allocating blocks in block bitmap corrupted group
    
    Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
    Reviewed-by: Jan Kara <jack@xxxxxxx>
    Link: https://lore.kernel.org/r/20240104142040.2835097-7-libaokun1@xxxxxxxxxx
    Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 48930df9ae565..3e4be376a479a 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2197,6 +2197,9 @@ int ext4_mb_try_best_found(struct ext4_allocation_context *ac,
 		return err;
 
 	ext4_lock_group(ac->ac_sb, group);
+	if (unlikely(EXT4_MB_GRP_BBITMAP_CORRUPT(e4b->bd_info)))
+		goto out;
+
 	max = mb_find_extent(e4b, ex.fe_start, ex.fe_len, &ex);
 
 	if (max > 0) {
@@ -2204,6 +2207,7 @@ int ext4_mb_try_best_found(struct ext4_allocation_context *ac,
 		ext4_mb_use_best_found(ac, e4b);
 	}
 
+out:
 	ext4_unlock_group(ac->ac_sb, group);
 	ext4_mb_unload_buddy(e4b);