linux-kernel - [PATCH 3.17 076/141] dm thin: grab a virtual cell before looking up the mapping

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Message-Id: <20141119205153.171682771@linuxfoundation.org>
Date:	Wed, 19 Nov 2014 12:51:39 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Joe Thornber <ejt@...hat.com>,
	Mike Snitzer <snitzer@...hat.com>
Subject: [PATCH 3.17 076/141] dm thin: grab a virtual cell before looking up the mapping

3.17-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Joe Thornber <ejt@...hat.com>

commit c822ed967cba38505713d59ed40a114386ef6c01 upstream.

Avoids normal IO racing with discard.

Signed-off-by: Joe Thornber <ejt@...hat.com>
Signed-off-by: Mike Snitzer <snitzer@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/md/dm-thin.c |   16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -1936,6 +1936,14 @@ static int thin_bio_map(struct dm_target
 		return DM_MAPIO_SUBMITTED;
 	}
 
+	/*
+	 * We must hold the virtual cell before doing the lookup, otherwise
+	 * there's a race with discard.
+	 */
+	build_virtual_key(tc->td, block, &key);
+	if (dm_bio_detain(tc->pool->prison, &key, bio, &cell1, &cell_result))
+		return DM_MAPIO_SUBMITTED;
+
 	r = dm_thin_find_block(td, block, 0, &result);
 
 	/*
@@ -1959,13 +1967,10 @@ static int thin_bio_map(struct dm_target
 			 * shared flag will be set in their case.
 			 */
 			thin_defer_bio(tc, bio);
+			cell_defer_no_holder_no_free(tc, &cell1);
 			return DM_MAPIO_SUBMITTED;
 		}
 
-		build_virtual_key(tc->td, block, &key);
-		if (dm_bio_detain(tc->pool->prison, &key, bio, &cell1, &cell_result))
-			return DM_MAPIO_SUBMITTED;
-
 		build_data_key(tc->td, result.block, &key);
 		if (dm_bio_detain(tc->pool->prison, &key, bio, &cell2, &cell_result)) {
 			cell_defer_no_holder_no_free(tc, &cell1);
@@ -1986,6 +1991,7 @@ static int thin_bio_map(struct dm_target
 			 * of doing so.
 			 */
 			handle_unserviceable_bio(tc->pool, bio);
+			cell_defer_no_holder_no_free(tc, &cell1);
 			return DM_MAPIO_SUBMITTED;
 		}
 		/* fall through */
@@ -1996,6 +2002,7 @@ static int thin_bio_map(struct dm_target
 		 * provide the hint to load the metadata into cache.
 		 */
 		thin_defer_bio(tc, bio);
+		cell_defer_no_holder_no_free(tc, &cell1);
 		return DM_MAPIO_SUBMITTED;
 
 	default:
@@ -2005,6 +2012,7 @@ static int thin_bio_map(struct dm_target
 		 * pool is switched to fail-io mode.
 		 */
 		bio_io_error(bio);
+		cell_defer_no_holder_no_free(tc, &cell1);
 		return DM_MAPIO_SUBMITTED;
 	}
 }


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