From 001fe0dab4eacd9e714b7c9de5f13af2bb3c3e1a Mon Sep 17 00:00:00 2001 From: Jiufei Xue Date: Sat, 6 Apr 2019 18:57:40 -0400 Subject: [PATCH] jbd2: check superblock mapped prior to committing commit 742b06b5628f2cd23cb51a034cb54dc33c6162c5 upstream. We hit a BUG at fs/buffer.c:3057 if we detached the nbd device before unmounting ext4 filesystem. The typical chain of events leading to the BUG: jbd2_write_superblock submit_bh submit_bh_wbc BUG_ON(!buffer_mapped(bh)); The block device is removed and all the pages are invalidated. JBD2 was trying to write journal superblock to the block device which is no longer present. Fix this by checking the journal superblock's buffer head prior to submitting. Reported-by: Eric Ren Signed-off-by: Jiufei Xue Signed-off-by: Theodore Ts'o Reviewed-by: Jan Kara Cc: stable@kernel.org Signed-off-by: Greg Kroah-Hartman --- fs/jbd2/journal.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c index 88f2a49..9e61877 100644 --- a/fs/jbd2/journal.c +++ b/fs/jbd2/journal.c @@ -1366,6 +1366,10 @@ static int jbd2_write_superblock(journal_t *journal, int write_flags) journal_superblock_t *sb = journal->j_superblock; int ret; + /* Buffer got discarded which means block device got invalidated */ + if (!buffer_mapped(bh)) + return -EIO; + trace_jbd2_write_superblock(journal, write_flags); if (!(journal->j_flags & JBD2_BARRIER)) write_flags &= ~(REQ_FUA | REQ_PREFLUSH); -- 2.7.4