jbd2: fix deadlock in jbd2_journal_cancel_revoke()

Commit f76d4c28a46a ("fs/jbd2: use sleeping version of
__find_get_block()") changed jbd2_journal_cancel_revoke() to use
__find_get_block_nonatomic() which holds the folio lock instead of
i_private_lock. This breaks the lock ordering (folio -> buffer) and
causes an ABBA deadlock when the filesystem blocksize < pagesize:

     T1                                T2
ext4_mkdir()
 ext4_init_new_dir()
  ext4_append()
   ext4_getblk()
    lock_buffer()    <- A
                                   sync_blockdev()
                                    blkdev_writepages()
                                     writeback_iter()
                                      writeback_get_folio()
                                       folio_lock()   <- B
     ext4_journal_get_create_access()
      jbd2_journal_cancel_revoke()
       __find_get_block_nonatomic()
        folio_lock()  <- B
                                     block_write_full_folio()
                                      lock_buffer()   <- A

This can occasionally cause generic/013 to hang.

Fix by only calling __find_get_block_nonatomic() when the passed
buffer_head doesn't belong to the bdev, which is the only case that we
need to look up its bdev alias. Otherwise, the lookup is redundant since
the found buffer_head is equal to the one we passed in.

Fixes: f76d4c28a46a ("fs/jbd2: use sleeping version of __find_get_block()")
Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Link: https://patch.msgid.link/20260409114204.917154-1-yi.zhang@huaweicloud.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org

fs/jbd2/revoke.c

diff --git a/fs/jbd2/revoke.c b/fs/jbd2/revoke.c
index 9016ddb..e4c2fbd 100644
--- a/fs/jbd2/revoke.c
+++ b/fs/jbd2/revoke.c
@@ -428,6 +428,7 @@ void jbd2_journal_cancel_revoke(handle_t *handle, struct journal_head *jh)
 	journal_t *journal = handle->h_transaction->t_journal;
 	int need_cancel;
 	struct buffer_head *bh = jh2bh(jh);
+	struct address_space *bh_mapping = bh->b_folio->mapping;
 
 	jbd2_debug(4, "journal_head %p, cancelling revoke\n", jh);
 
@@ -464,13 +465,14 @@ void jbd2_journal_cancel_revoke(handle_t *handle, struct journal_head *jh)
 	 * buffer_head?  If so, we'd better make sure we clear the
 	 * revoked status on any hashed alias too, otherwise the revoke
 	 * state machine will get very upset later on. */
-	if (need_cancel) {
+	if (need_cancel && !sb_is_blkdev_sb(bh_mapping->host->i_sb)) {
 		struct buffer_head *bh2;
+
 		bh2 = __find_get_block_nonatomic(bh->b_bdev, bh->b_blocknr,
 						 bh->b_size);
 		if (bh2) {
-			if (bh2 != bh)
-				clear_buffer_revoked(bh2);
+			WARN_ON_ONCE(bh2 == bh);
+			clear_buffer_revoked(bh2);
 			__brelse(bh2);
 		}
 	}