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")
Signed-off-by: Benjamin Marzinski <bmarz...@redhat.com>
---
drivers/md/dm.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index d8f16183bf27..c7d2dbf03ccb 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -544,17 +544,20 @@ static void dm_start_io_acct(struct dm_io *io, struct bio
*clone)
{
/*
* Ensure IO accounting is only ever started once.
+ * Expect no possibility for race unless DM_TIO_IS_DUPLICATE_BIO.
*/
- if (dm_io_flagged(io, DM_IO_ACCOUNTED))
- return;
-
- /* Expect no possibility for race unless DM_TIO_IS_DUPLICATE_BIO. */
if (!clone || likely(dm_tio_is_normal(clone_to_tio(clone)))) {
+ if (WARN_ON_ONCE(dm_io_flagged(io, DM_IO_ACCOUNTED)))
+ return;
dm_io_set_flag(io, DM_IO_ACCOUNTED);
} else {
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);
}
--
2.30.2
--
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