[PATCH V7 5/6] block: support PREEMPT_ONLY
From: Ming Lei <hidden>
Date: 2017-09-30 06:13:36
Also in:
linux-scsi, lkml
Subsystem:
block layer, the rest · Maintainers:
Jens Axboe, Linus Torvalds
When queue is in PREEMPT_ONLY mode, only RQF_PREEMPT request can be allocated and dispatched, other requests won't be allowed to enter I/O path. This is useful for supporting safe SCSI quiesce. Part of this patch is from Bart's '[PATCH v4 4∕7] block: Add the QUEUE_FLAG_PREEMPT_ONLY request queue flag'. Tested-by: Oleksandr Natalenko <redacted> Tested-by: Martin Steigerwald <redacted> Cc: Bart Van Assche <redacted> Signed-off-by: Ming Lei <redacted> --- block/blk-core.c | 26 ++++++++++++++++++++++++-- include/linux/blkdev.h | 5 +++++ 2 files changed, 29 insertions(+), 2 deletions(-)
diff --git a/block/blk-core.c b/block/blk-core.c
index 95b1c5e50be3..bb683bfe37b2 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c@@ -346,6 +346,17 @@ void blk_sync_queue(struct request_queue *q) } EXPORT_SYMBOL(blk_sync_queue); +void blk_set_preempt_only(struct request_queue *q, bool preempt_only) +{ + blk_mq_freeze_queue(q); + if (preempt_only) + queue_flag_set_unlocked(QUEUE_FLAG_PREEMPT_ONLY, q); + else + queue_flag_clear_unlocked(QUEUE_FLAG_PREEMPT_ONLY, q); + blk_mq_unfreeze_queue(q); +} +EXPORT_SYMBOL(blk_set_preempt_only); + /** * __blk_run_queue_uncond - run a queue whether or not it has been stopped * @q: The queue to run
@@ -771,9 +782,18 @@ int blk_queue_enter(struct request_queue *q, unsigned flags) while (true) { int ret; + /* + * preempt_only flag has to be set after queue is frozen, + * so it can be checked here lockless and safely + */ + if (blk_queue_preempt_only(q)) { + if (!(flags & BLK_REQ_PREEMPT)) + goto slow_path; + } + if (percpu_ref_tryget_live(&q->q_usage_counter)) return 0; - + slow_path: if (flags & BLK_REQ_NOWAIT) return -EBUSY;
@@ -787,7 +807,9 @@ int blk_queue_enter(struct request_queue *q, unsigned flags) smp_rmb(); ret = wait_event_interruptible(q->mq_freeze_wq, - !atomic_read(&q->mq_freeze_depth) || + (!atomic_read(&q->mq_freeze_depth) && + ((flags & BLK_REQ_PREEMPT) || + !blk_queue_preempt_only(q))) || blk_queue_dying(q)); if (blk_queue_dying(q)) return -ENODEV;
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 68445adc8765..b01a0c6bb1f0 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h@@ -631,6 +631,7 @@ struct request_queue { #define QUEUE_FLAG_REGISTERED 26 /* queue has been registered to a disk */ #define QUEUE_FLAG_SCSI_PASSTHROUGH 27 /* queue supports SCSI commands */ #define QUEUE_FLAG_QUIESCED 28 /* queue has been quiesced */ +#define QUEUE_FLAG_PREEMPT_ONLY 29 /* only process REQ_PREEMPT requests */ #define QUEUE_FLAG_DEFAULT ((1 << QUEUE_FLAG_IO_STAT) | \ (1 << QUEUE_FLAG_STACKABLE) | \
@@ -735,6 +736,10 @@ static inline void queue_flag_clear(unsigned int flag, struct request_queue *q) ((rq)->cmd_flags & (REQ_FAILFAST_DEV|REQ_FAILFAST_TRANSPORT| \ REQ_FAILFAST_DRIVER)) #define blk_queue_quiesced(q) test_bit(QUEUE_FLAG_QUIESCED, &(q)->queue_flags) +#define blk_queue_preempt_only(q) \ + test_bit(QUEUE_FLAG_PREEMPT_ONLY, &(q)->queue_flags) + +extern void blk_set_preempt_only(struct request_queue *q, bool preempt_only); static inline bool blk_account_rq(struct request *rq) {
--
2.9.5