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From: Hannes Reinecke <hare@suse.de>
To: Ilya Dryomov <idryomov@gmail.com>
Cc: Sage Weil <sage@redhat.com>, Daniel Disseldorp <ddiss@suse.com>,
	Jens Axboe <axboe@kernel.dk>,
	ceph-devel@vger.kernel.org, linux-block@vger.kernel.org,
	Hannes Reinecke <hare@suse.de>
Subject: [PATCH 02/15] rbd: use READ_ONCE() when checking the mapping size
Date: Fri, 31 Jan 2020 11:37:26 +0100	[thread overview]
Message-ID: <20200131103739.136098-3-hare@suse.de> (raw)
In-Reply-To: <20200131103739.136098-1-hare@suse.de>

The mapping size is changed only very infrequently, so we don't
need to take the header mutex for checking; using READ_ONCE()
is sufficient here. And it avoids having to take a mutex in the
hot path.

Signed-off-by: Hannes Reinecke <hare@suse.de>
---
 drivers/block/rbd.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index db80b964d8ea..792180548e89 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -4788,13 +4788,13 @@ static void rbd_queue_workfn(struct work_struct *work)
 
 	blk_mq_start_request(rq);
 
-	down_read(&rbd_dev->header_rwsem);
-	mapping_size = rbd_dev->mapping.size;
+	mapping_size = READ_ONCE(rbd_dev->mapping.size);
 	if (op_type != OBJ_OP_READ) {
+		down_read(&rbd_dev->header_rwsem);
 		snapc = rbd_dev->header.snapc;
 		ceph_get_snap_context(snapc);
+		up_read(&rbd_dev->header_rwsem);
 	}
-	up_read(&rbd_dev->header_rwsem);
 
 	if (offset + length > mapping_size) {
 		rbd_warn(rbd_dev, "beyond EOD (%llu~%llu > %llu)", offset,
@@ -4981,9 +4981,9 @@ static int rbd_dev_refresh(struct rbd_device *rbd_dev)
 	u64 mapping_size;
 	int ret;
 
-	down_write(&rbd_dev->header_rwsem);
-	mapping_size = rbd_dev->mapping.size;
+	mapping_size = READ_ONCE(rbd_dev->mapping.size);
 
+	down_write(&rbd_dev->header_rwsem);
 	ret = rbd_dev_header_info(rbd_dev);
 	if (ret)
 		goto out;
@@ -4999,7 +4999,7 @@ static int rbd_dev_refresh(struct rbd_device *rbd_dev)
 	}
 
 	rbd_assert(!rbd_is_snap(rbd_dev));
-	rbd_dev->mapping.size = rbd_dev->header.image_size;
+	WRITE_ONCE(rbd_dev->mapping.size, rbd_dev->header.image_size);
 
 out:
 	up_write(&rbd_dev->header_rwsem);
-- 
2.16.4


  parent reply	other threads:[~2020-01-31 10:38 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-31 10:37 [PATCH 00/15] rbd: switch to blk-mq Hannes Reinecke
2020-01-31 10:37 ` [PATCH 01/15] rbd: lock object request list Hannes Reinecke
2020-02-03 16:38   ` Ilya Dryomov
2020-01-31 10:37 ` Hannes Reinecke [this message]
2020-02-03 16:50   ` [PATCH 02/15] rbd: use READ_ONCE() when checking the mapping size Ilya Dryomov
2020-02-04  7:05     ` Hannes Reinecke
2020-01-31 10:37 ` [PATCH 03/15] rbd: reorder rbd_img_advance() Hannes Reinecke
2020-01-31 10:37 ` [PATCH 04/15] rbd: reorder switch statement in rbd_advance_read() Hannes Reinecke
2020-01-31 10:37 ` [PATCH 05/15] rbd: reorder switch statement in rbd_advance_write() Hannes Reinecke
2020-01-31 10:37 ` [PATCH 06/15] rbd: add 'done' state for rbd_obj_advance_copyup() Hannes Reinecke
2020-01-31 10:37 ` [PATCH 07/15] rbd: use callback for image request completion Hannes Reinecke
2020-02-03 17:13   ` Ilya Dryomov
2020-01-31 10:37 ` [PATCH 08/15] rbd: add debugging statements for the state machine Hannes Reinecke
2020-01-31 10:37 ` [PATCH 09/15] rbd: count pending object requests in-line Hannes Reinecke
2020-02-03 17:47   ` Ilya Dryomov
2020-02-04  6:59     ` Hannes Reinecke
2020-01-31 10:37 ` [PATCH 10/15] rbd: kill 'work_result' Hannes Reinecke
2020-01-31 10:37 ` [PATCH 11/15] rbd: drop state_mutex in __rbd_img_handle_request() Hannes Reinecke
2020-02-03 18:01   ` Ilya Dryomov
2020-01-31 10:37 ` [PATCH 12/15] rbd: kill img_request kref Hannes Reinecke
2020-01-31 10:37 ` [PATCH 13/15] rbd: schedule image_request after preparation Hannes Reinecke
2020-02-03 18:40   ` Ilya Dryomov
2020-01-31 10:37 ` [PATCH 14/15] rbd: embed image request as blk_mq request payload Hannes Reinecke
2020-01-31 10:37 ` [PATCH 15/15] rbd: switch to blk-mq Hannes Reinecke
2020-02-03  8:36   ` Christoph Hellwig

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