dm: fix race in dm_start_io_acct

commit 10eb3a0d517fcc83eeea4242c149461205675eb4 upstream.

After commit 82f6cdcc3676c ("dm: switch dm_io booleans over to proper
flags") dm_start_io_acct stopped atomically checking and setting
was_accounted, which turned into the DM_IO_ACCOUNTED flag. This opened
the possibility for a race where IO accounting is started twice for
duplicate bios. To remove the race, check the flag while holding the
io->lock.

Fixes: 82f6cdcc3676c ("dm: switch dm_io booleans over to proper flags")
Cc: stable@vger.kernel.org
Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 82957bd460e894556fed5eed0b991c14f3c0713b..a68316f96350d0af64c1db865c48d1e97fbf95ca 100644 (file)
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -551,6 +551,10 @@ static void dm_start_io_acct(struct dm_io *io, struct bio *clone)
                        return;
                /* Can afford locking given DM_TIO_IS_DUPLICATE_BIO */
                spin_lock_irqsave(&io->lock, flags);
+               if (dm_io_flagged(io, DM_IO_ACCOUNTED)) {
+                       spin_unlock_irqrestore(&io->lock, flags);
+                       return;
+               }
                dm_io_set_flag(io, DM_IO_ACCOUNTED);
                spin_unlock_irqrestore(&io->lock, flags);
        }