[PATCH 1/3] block: Initialize ->queue_lock to internal lock at queue allocation time

From: Vivek Goyal
Date: Mon Feb 28 2011 - 14:26:25 EST

o There does not seem to be a clear convention whether q->queue_lock is
initialized or not when blk_cleanup_queue() is called. In the past
it was not necessary but now blk_throtl_exit() takes up queue lock
by default and needs queue lock to be available.

In fact elevator_exit() code also has similar requirement just that
it is less stringent in the sense that elevator_exit() is called only
if elevator is initialized.

o Two problems have been noticed because of ambiguity about spin lock

- If a driver calls blk_alloc_queue() and then soon calls
blk_cleanup_queue() almost immediately, (because some other driver
structure allocation failed or some other error happened) then
blk_throtl_exit() will run into issues as queue lock is not
initialized. Loop driver ran into this issue recently and I noticed
error paths in md driver too. Similar error paths should exist in
other drivers too.

- If some driver provided external spin lock and zapped the lock
before blk_cleanup_queue(), then it can lead to issues.

o So this patch initializes the default queue lock at queue allocation time.
block throttling code is one of the users of queue lock and it is
initialized at the queue allocation time, so it makes sense to
initialize ->queue_lock also to internal lock. A driver can overide that
lock later. This will take care of the issue where a driver does not have
to worry about initializing the queue lock to default before calling

Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx>
block/blk-core.c | 16 +++++++++++++++-
block/blk-settings.c | 7 -------
2 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 3cc17e6..bc2b7c5 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -446,6 +446,11 @@ void blk_put_queue(struct request_queue *q)

+ * Note: If a driver supplied the queue lock, it should not zap that lock
+ * unexpectedly as some queue cleanup components like elevator_exit() and
+ * blk_throtl_exit() need queue lock.
+ */
void blk_cleanup_queue(struct request_queue *q)
@@ -540,6 +545,12 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)

+ /*
+ * By default initialize queue_lock to internal lock and driver can
+ * override it later if need be.
+ */
+ q->queue_lock = &q->__queue_lock;
return q;
@@ -624,7 +635,10 @@ blk_init_allocated_queue_node(struct request_queue *q, request_fn_proc *rfn,
q->unprep_rq_fn = NULL;
q->unplug_fn = generic_unplug_device;
q->queue_flags = QUEUE_FLAG_DEFAULT;
- q->queue_lock = lock;
+ /* Override internal queue lock with supplied lock pointer */
+ if (lock)
+ q->queue_lock = lock;

* This also sets hw/phys segments, boundary and size
diff --git a/block/blk-settings.c b/block/blk-settings.c
index 36c8c1f..df649fa 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -176,13 +176,6 @@ void blk_queue_make_request(struct request_queue *q, make_request_fn *mfn)
blk_queue_max_hw_sectors(q, BLK_SAFE_MAX_SECTORS);

- * If the caller didn't supply a lock, fall back to our embedded
- * per-queue locks
- */
- if (!q->queue_lock)
- q->queue_lock = &q->__queue_lock;
- /*
* by default assume old behaviour and bounce for any highmem page
blk_queue_bounce_limit(q, BLK_BOUNCE_HIGH);

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