dm: fix race in dm_start_io_acct

After commit f12fa097000ab ("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: f12fa097000ab ("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>

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index d8f16183bf27ce9f4478e814da6f2cb91fe82b6d..d5e6d33700e504113e5932f16012ba0ddde94da0 100644 (file)
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -555,6 +555,10 @@ static void dm_start_io_acct(struct dm_io *io, struct bio *clone)
                unsigned long flags;
                /* 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);
        }