[PATCH 5.18 119/141] dm: fix race in dm_start_io_acct

Greg Kroah-Hartman
2022-06-20T13:06:56Z

From: Benjamin Marzinski <bmarzins@redhat.com>

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>
---
drivers/md/dm.c | 4 ++++
1 file changed, 4 insertions(+)

--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -551,6 +551,10 @@ static void dm_start_io_acct(struct dm_i
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);
}