4.9-stable review patch. If anyone has any objections, please let me know.
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From: Jan Kara jack@suse.cz
commit ccd3c4373eacb044eb3832966299d13d2631f66f upstream.
The code cleaning transaction's lists of checkpoint buffers has a bug where it increases bh refcount only after releasing journal->j_list_lock. Thus the following race is possible:
CPU0 CPU1 jbd2_log_do_checkpoint() jbd2_journal_try_to_free_buffers() __journal_try_to_free_buffer(bh) ... while (transaction->t_checkpoint_io_list) ... if (buffer_locked(bh)) {
<-- IO completes now, buffer gets unlocked -->
spin_unlock(&journal->j_list_lock); spin_lock(&journal->j_list_lock); __jbd2_journal_remove_checkpoint(jh); spin_unlock(&journal->j_list_lock); try_to_free_buffers(page); get_bh(bh) <-- accesses freed bh
Fix the problem by grabbing bh reference before unlocking journal->j_list_lock.
Fixes: dc6e8d669cf5 ("jbd2: don't call get_bh() before calling __jbd2_journal_remove_checkpoint()") Fixes: be1158cc615f ("jbd2: fold __process_buffer() into jbd2_log_do_checkpoint()") Reported-by: syzbot+7f4a27091759e2fe7453@syzkaller.appspotmail.com CC: stable@vger.kernel.org Reviewed-by: Lukas Czerner lczerner@redhat.com Signed-off-by: Jan Kara jack@suse.cz Signed-off-by: Theodore Ts'o tytso@mit.edu Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/jbd2/checkpoint.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- a/fs/jbd2/checkpoint.c +++ b/fs/jbd2/checkpoint.c @@ -254,8 +254,8 @@ restart: bh = jh2bh(jh);
if (buffer_locked(bh)) { - spin_unlock(&journal->j_list_lock); get_bh(bh); + spin_unlock(&journal->j_list_lock); wait_on_buffer(bh); /* the journal_head may have gone by now */ BUFFER_TRACE(bh, "brelse"); @@ -336,8 +336,8 @@ restart2: jh = transaction->t_checkpoint_io_list; bh = jh2bh(jh); if (buffer_locked(bh)) { - spin_unlock(&journal->j_list_lock); get_bh(bh); + spin_unlock(&journal->j_list_lock); wait_on_buffer(bh); /* the journal_head may have gone by now */ BUFFER_TRACE(bh, "brelse");