[PATCH V2 6/8] block: allow to allocate req with REQF_PREEMPT when queue is frozen

Ming Lei
2017-09-01T18:51:45Z

REQF_PREEMPT is a bit special because it is required to be
dispatched to lld even when SCSI device is quiesced.

So this patch introduces __blk_get_request() to allow block
layer to allocate request when queue is frozen, since we
will freeze queue before quiescing SCSI device in the
following patch for supporting safe SCSI quiescing.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
block/blk-core.c | 25 +++++++++++++++++--------
block/blk-mq.c | 11 +++++++++--
block/blk.h | 5 +++++
include/linux/blk-mq.h | 7 ++++---
include/linux/blkdev.h | 17 +++++++++++++++--
5 files changed, 50 insertions(+), 15 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 85b15833a7a5..c199910d4fe1 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1402,7 +1402,8 @@ static struct request *get_request(struct request_queue *q, unsigned int op,
}

static struct request *blk_old_get_request(struct request_queue *q,
- unsigned int op, gfp_t gfp_mask)
+ unsigned int op, gfp_t gfp_mask,
+ unsigned int flags)
{
struct request *rq;
int ret = 0;
@@ -1412,9 +1413,17 @@ static struct request *blk_old_get_request(struct request_queue *q,
/* create ioc upfront */
create_io_context(gfp_mask, q->node);

- ret = blk_queue_enter(q, !(gfp_mask & __GFP_DIRECT_RECLAIM));
+ /*
+ * When queue is frozen, we still need to allocate req for
+ * REQF_PREEMPT.
+ */
+ if ((flags & BLK_MQ_REQ_PREEMPT) && blk_queue_is_freezing(q))
+ blk_queue_enter_live(q);
+ else
+ ret = blk_queue_enter(q, !(gfp_mask & __GFP_DIRECT_RECLAIM));
if (ret)
return ERR_PTR(ret);
+
spin_lock_irq(q->queue_lock);
rq = get_request(q, op, NULL, gfp_mask);
if (IS_ERR(rq)) {
@@ -1430,26 +1439,26 @@ static struct request *blk_old_get_request(struct request_queue *q,
return rq;
}

-struct request *blk_get_request(struct request_queue *q, unsigned int op,
- gfp_t gfp_mask)
+struct request *__blk_get_request(struct request_queue *q, unsigned int op,
+ gfp_t gfp_mask, unsigned int flags)
{
struct request *req;

if (q->mq_ops) {
req = blk_mq_alloc_request(q, op,
- (gfp_mask & __GFP_DIRECT_RECLAIM) ?
- 0 : BLK_MQ_REQ_NOWAIT);
+ flags | ((gfp_mask & __GFP_DIRECT_RECLAIM) ?
+ 0 : BLK_MQ_REQ_NOWAIT));
if (!IS_ERR(req) && q->mq_ops->initialize_rq_fn)
q->mq_ops->initialize_rq_fn(req);
} else {
- req = blk_old_get_request(q, op, gfp_mask);
+ req = blk_old_get_request(q, op, gfp_mask, flags);
if (!IS_ERR(req) && q->initialize_rq_fn)
q->initialize_rq_fn(req);
}

return req;
}
-EXPORT_SYMBOL(blk_get_request);
+EXPORT_SYMBOL(__blk_get_request);

/**
* blk_requeue_request - put a request back on queue
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 24de78afbe9a..695d2eeaf41a 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -382,9 +382,16 @@ struct request *blk_mq_alloc_request(struct request_queue *q, unsigned int op,
{
struct blk_mq_alloc_data alloc_data = { .flags = flags };
struct request *rq;
- int ret;
+ int ret = 0;

- ret = blk_queue_enter(q, flags & BLK_MQ_REQ_NOWAIT);
+ /*
+ * When queue is frozen, we still need to allocate req for
+ * REQF_PREEMPT.
+ */
+ if ((flags & BLK_MQ_REQ_PREEMPT) && blk_queue_is_freezing(q))
+ blk_queue_enter_live(q);
+ else
+ ret = blk_queue_enter(q, flags & BLK_MQ_REQ_NOWAIT);
if (ret)
return ERR_PTR(ret);

diff --git a/block/blk.h b/block/blk.h
index 242486e26a81..b71f8cc047aa 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -80,6 +80,11 @@ static inline void blk_queue_enter_live(struct request_queue *q)
percpu_ref_get(&q->q_usage_counter);
}

+static inline bool blk_queue_is_freezing(struct request_queue *q)
+{
+ return percpu_ref_is_dying(&q->q_usage_counter);
+}
+
#ifdef CONFIG_BLK_DEV_INTEGRITY
void blk_flush_integrity(void);
bool __bio_integrity_endio(struct bio *);
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index f90d78eb85df..0ba5cb043172 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -200,9 +200,10 @@ void blk_mq_free_request(struct request *rq);
bool blk_mq_can_queue(struct blk_mq_hw_ctx *);

enum {
- BLK_MQ_REQ_NOWAIT = (1 << 0), /* return when out of requests */
- BLK_MQ_REQ_RESERVED = (1 << 1), /* allocate from reserved pool */
- BLK_MQ_REQ_INTERNAL = (1 << 2), /* allocate internal/sched tag */
+ BLK_MQ_REQ_PREEMPT = BLK_REQ_PREEMPT, /* allocate for RQF_PREEMPT */
+ BLK_MQ_REQ_NOWAIT = (1 << 8), /* return when out of requests */
+ BLK_MQ_REQ_RESERVED = (1 << 9), /* allocate from reserved pool */
+ BLK_MQ_REQ_INTERNAL = (1 << 10), /* allocate internal/sched tag */
};

struct request *blk_mq_alloc_request(struct request_queue *q, unsigned int op,
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index f45f157b2910..a43422f5379a 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -858,6 +858,11 @@ enum {
BLKPREP_INVALID, /* invalid command, kill, return -EREMOTEIO */
};

+/* passed to __blk_get_request */
+enum {
+ BLK_REQ_PREEMPT = (1 << 0), /* allocate for RQF_PREEMPT */
+};
+
extern unsigned long blk_max_low_pfn, blk_max_pfn;

/*
@@ -940,8 +945,9 @@ extern void blk_rq_init(struct request_queue *q, struct request *rq);
extern void blk_init_request_from_bio(struct request *req, struct bio *bio);
extern void blk_put_request(struct request *);
extern void __blk_put_request(struct request_queue *, struct request *);
-extern struct request *blk_get_request(struct request_queue *, unsigned int op,
- gfp_t gfp_mask);
+extern struct request *__blk_get_request(struct request_queue *,
+ unsigned int op, gfp_t gfp_mask,
+ unsigned int flags);
extern void blk_requeue_request(struct request_queue *, struct request *);
extern int blk_lld_busy(struct request_queue *q);
extern int blk_rq_prep_clone(struct request *rq, struct request *rq_src,
@@ -992,6 +998,13 @@ blk_status_t errno_to_blk_status(int errno);

bool blk_mq_poll(struct request_queue *q, blk_qc_t cookie);

+static inline struct request *blk_get_request(struct request_queue *q,
+ unsigned int op,
+ gfp_t gfp_mask)
+{
+ return __blk_get_request(q, op, gfp_mask, 0);
+}
+
static inline struct request_queue *bdev_get_queue(struct block_device *bdev)
{
return bdev->bd_disk->queue; /* this is never NULL */
--
2.9.5