linux-kernel - [PATCH 5.18 119/141] dm: fix race in dm_start_io

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Date:   Mon, 20 Jun 2022 14:50:57 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Benjamin Marzinski <bmarzins@...hat.com>,
        Mike Snitzer <snitzer@...nel.org>
Subject: [PATCH 5.18 119/141] dm: fix race in dm_start_io_acct

From: Benjamin Marzinski <bmarzins@...hat.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@...r.kernel.org
Signed-off-by: Benjamin Marzinski <bmarzins@...hat.com>
Signed-off-by: Mike Snitzer <snitzer@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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);
 	}