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Date: Thu, 28 Mar 2019 18:07:50 +0800 From: Jiufei Xue <jiufei.xue@...ux.alibaba.com> To: linux-ext4@...r.kernel.org Cc: tytso@....edu, jack@...e.cz, renzhen@...ux.alibaba.com Subject: [PATCH v2] jbd2: check superblock mapped prior to committing 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. Cc: stable@...nel.org Reported-by: Eric Ren <renzhen@...ux.alibaba.com> Signed-off-by: Jiufei Xue <jiufei.xue@...ux.alibaba.com> Reviewed-by: Jan Kara <jack@...e.cz> --- fs/jbd2/journal.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c index 382c030cc78b..37e16d969925 100644 --- a/fs/jbd2/journal.c +++ b/fs/jbd2/journal.c @@ -1350,6 +1350,10 @@ 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); -- 2.19.1.856.g8858448bb
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