On 10/26/16 18:30, Ming Lei wrote:
On Thu, Oct 27, 2016 at 6:53 AM, Bart Van Assche
<bart.vanass...@sandisk.com> wrote:
blk_mq_quiesce_queue() waits until ongoing .queue_rq() invocations
have finished. This function does *not* wait until all outstanding
requests have finished (this means invocation of request.end_io()).
The algorithm used by blk_mq_quiesce_queue() is as follows:
* Hold either an RCU read lock or an SRCU read lock around
.queue_rq() calls. The former is used if .queue_rq() does not
block and the latter if .queue_rq() may block.
* blk_mq_quiesce_queue() calls synchronize_srcu() or
synchronize_rcu() to wait for .queue_rq() invocations that
started before blk_mq_quiesce_queue() was called.
* The blk_mq_hctx_stopped() calls that control whether or not
.queue_rq() will be called are called with the (S)RCU read lock
held. This is necessary to avoid race conditions against
the "blk_mq_stop_hw_queues(q); blk_mq_quiesce_queue(q);"
sequence from another thread.
Signed-off-by: Bart Van Assche <bart.vanass...@sandisk.com>
Cc: Christoph Hellwig <h...@lst.de>
Cc: Ming Lei <tom.leim...@gmail.com>
Cc: Hannes Reinecke <h...@suse.com>
Cc: Johannes Thumshirn <jthumsh...@suse.de>
---
block/Kconfig | 1 +
block/blk-mq.c | 69 +++++++++++++++++++++++++++++++++++++++++++++-----
include/linux/blk-mq.h | 3 +++
include/linux/blkdev.h | 1 +
4 files changed, 67 insertions(+), 7 deletions(-)
diff --git a/block/Kconfig b/block/Kconfig
index 1d4d624..0562ef9 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -5,6 +5,7 @@ menuconfig BLOCK
bool "Enable the block layer" if EXPERT
default y
select SBITMAP
+ select SRCU
help
Provide block layer support for the kernel.
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 0cf21c2..4945437 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -115,6 +115,31 @@ void blk_mq_unfreeze_queue(struct request_queue *q)
}
EXPORT_SYMBOL_GPL(blk_mq_unfreeze_queue);
+/**
+ * blk_mq_quiesce_queue() - wait until all ongoing queue_rq calls have finished
+ * @q: request queue.
+ *
+ * Note: this function does not prevent that the struct request end_io()
+ * callback function is invoked. Additionally, it is not prevented that
+ * new queue_rq() calls occur unless the queue has been stopped first.
+ */
+void blk_mq_quiesce_queue(struct request_queue *q)
+{
+ struct blk_mq_hw_ctx *hctx;
+ unsigned int i;
+ bool rcu = false;
Before synchronizing SRCU/RCU, we have to set a per-hctx flag
or per-queue flag to block comming .queue_rq(), seems I mentioned
that before:
https://www.spinics.net/lists/linux-rdma/msg41389.html
Hello Ming,
Thanks for having included an URL to an archived version of that
discussion. What I remember about that discussion is that I proposed to
use the existing flag BLK_MQ_S_STOPPED instead of introducing a
new QUEUE_FLAG_QUIESCING flag and that you agreed with that proposal.
See also https://www.spinics.net/lists/linux-rdma/msg41430.html.
Bart.
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