On Mon, Oct 09, 2017 at 04:14:00PM -0700, Bart Van Assche wrote:
> The contexts from which a SCSI device can be quiesced or resumed are:
> * Writing into /sys/class/scsi_device/*/device/state.
> * SCSI parallel (SPI) domain validation.
> * The SCSI device power management methods. See also scsi_bus_pm_ops.
>
> It is essential during suspend and resume that neither the filesystem
> state nor the filesystem metadata in RAM changes. This is why while
> the hibernation image is being written or restored that SCSI devices
> are quiesced. The SCSI core quiesces devices through scsi_device_quiesce()
> and scsi_device_resume(). In the SDEV_QUIESCE state execution of
> non-preempt requests is deferred. This is realized by returning
> BLKPREP_DEFER from inside scsi_prep_state_check() for quiesced SCSI
> devices. Avoid that a full queue prevents power management requests
> to be submitted by deferring allocation of non-preempt requests for
> devices in the quiesced state. This patch has been tested by running
> the following commands and by verifying that after resume the fio job
> is still running:
>
> for d in /sys/class/block/sd*[a-z]; do
> hcil=$(readlink "$d/device")
> hcil=${hcil#../../../}
> echo 4 > "$d/queue/nr_requests"
> echo 1 > "/sys/class/scsi_device/$hcil/device/queue_depth"
> done
> bdev=$(readlink /dev/disk/by-uuid/5217d83f-213e-4b42-b86e-20013325ba6c)
> bdev=${bdev#../../}
> hcil=$(readlink "/sys/block/$bdev/device")
> hcil=${hcil#../../../}
> fio --name="$bdev" --filename="/dev/$bdev" --buffered=0 --bs=512 --rw=randread \
> --ioengine=libaio --numjobs=4 --iodepth=16 --iodepth_batch=1 --thread \
> --loops=$((2**31)) &
> pid=$!
> sleep 1
> systemctl hibernate
> sleep 10
> kill $pid
>
> Reported-by: Oleksandr Natalenko <oleksandr@xxxxxxxxxxxxxx>
> References: "I/O hangs after resuming from suspend-to-ram" (https://marc.info/?l=linux-block&m=150340235201348).
> Signed-off-by: Bart Van Assche <bart.vanassche@xxxxxxx>
> Cc: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
> Cc: Ming Lei <ming.lei@xxxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: Hannes Reinecke <hare@xxxxxxxx>
> Cc: Johannes Thumshirn <jthumshirn@xxxxxxx>
> ---
> block/blk-core.c | 42 +++++++++++++++++++++++++++++++++++-------
> block/blk-mq.c | 4 ++--
> block/blk-timeout.c | 2 +-
> drivers/scsi/scsi_lib.c | 28 ++++++++++++++++++----------
> fs/block_dev.c | 4 ++--
> include/linux/blkdev.h | 2 +-
> 6 files changed, 59 insertions(+), 23 deletions(-)
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index ed992cbd107f..3847ea42e341 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -372,6 +372,7 @@ void blk_clear_preempt_only(struct request_queue *q)
>
> spin_lock_irqsave(q->queue_lock, flags);
> queue_flag_clear(QUEUE_FLAG_PREEMPT_ONLY, q);
> + wake_up_all(&q->mq_freeze_wq);
> spin_unlock_irqrestore(q->queue_lock, flags);
> }
> EXPORT_SYMBOL_GPL(blk_clear_preempt_only);
> @@ -793,15 +794,40 @@ struct request_queue *blk_alloc_queue(gfp_t gfp_mask)
> }
> EXPORT_SYMBOL(blk_alloc_queue);
>
> -int blk_queue_enter(struct request_queue *q, bool nowait)
> +/**
> + * blk_queue_enter() - try to increase q->q_usage_counter
> + * @q: request queue pointer
> + * @flags: BLK_MQ_REQ_NOWAIT and/or BLK_MQ_REQ_PREEMPT
> + */
> +int blk_queue_enter(struct request_queue *q, unsigned int flags)
> {
> + const bool preempt = flags & BLK_MQ_REQ_PREEMPT;
> +
> while (true) {
> + bool success = false;
> int ret;
>
> - if (percpu_ref_tryget_live(&q->q_usage_counter))
> + rcu_read_lock_sched();
> + if (percpu_ref_tryget_live(&q->q_usage_counter)) {
> + /*
> + * The code that sets the PREEMPT_ONLY flag is
> + * responsible for ensuring that that flag is globally
> + * visible before the queue is unfrozen.
> + */
> + if (preempt || !blk_queue_preempt_only(q)) {
> + success = true;
> + } else {
> + percpu_ref_put(&q->q_usage_counter);
> + WARN_ONCE("%s: Attempt to allocate non-preempt request in preempt-only mode.\n",
> + kobject_name(q->kobj.parent));
> + }
> + }
> + rcu_read_unlock_sched();
> +
> + if (success)
> return 0;
>
> - if (nowait)
> + if (flags & BLK_MQ_REQ_NOWAIT)
> return -EBUSY;
>
> /*
> @@ -814,7 +840,8 @@ int blk_queue_enter(struct request_queue *q, bool nowait)
> smp_rmb();
>
> ret = wait_event_interruptible(q->mq_freeze_wq,
> - !atomic_read(&q->mq_freeze_depth) ||
> + (atomic_read(&q->mq_freeze_depth) == 0 &&
> + (preempt || !blk_queue_preempt_only(q))) ||
> blk_queue_dying(q));
> if (blk_queue_dying(q))
> return -ENODEV;
> @@ -1442,8 +1469,7 @@ 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) ||
> - (op & REQ_NOWAIT));
> + ret = blk_queue_enter(q, flags);
> if (ret)
> return ERR_PTR(ret);
> spin_lock_irq(q->queue_lock);
> @@ -2264,8 +2290,10 @@ blk_qc_t generic_make_request(struct bio *bio)
> current->bio_list = bio_list_on_stack;
> do {
> struct request_queue *q = bio->bi_disk->queue;
> + unsigned int flags = bio->bi_opf & REQ_NOWAIT ?
> + BLK_MQ_REQ_NOWAIT : 0;
>
> - if (likely(blk_queue_enter(q, bio->bi_opf & REQ_NOWAIT) == 0)) {
> + if (likely(blk_queue_enter(q, flags) == 0)) {
> struct bio_list lower, same;
>
> /* Create a fresh bio_list for all subordinate requests */
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index bdbfe760bda0..44a06e8541f2 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -386,7 +386,7 @@ struct request *blk_mq_alloc_request(struct request_queue *q, unsigned int op,
> struct request *rq;
> int ret;
>
> - ret = blk_queue_enter(q, flags & BLK_MQ_REQ_NOWAIT);
> + ret = blk_queue_enter(q, flags);
> if (ret)
> return ERR_PTR(ret);
>
> @@ -425,7 +425,7 @@ struct request *blk_mq_alloc_request_hctx(struct request_queue *q,
> if (hctx_idx >= q->nr_hw_queues)
> return ERR_PTR(-EIO);
>
> - ret = blk_queue_enter(q, true);
> + ret = blk_queue_enter(q, flags);
> if (ret)
> return ERR_PTR(ret);
>
> diff --git a/block/blk-timeout.c b/block/blk-timeout.c
> index e3e9c9771d36..1eba71486716 100644
> --- a/block/blk-timeout.c
> +++ b/block/blk-timeout.c
> @@ -134,7 +134,7 @@ void blk_timeout_work(struct work_struct *work)
> struct request *rq, *tmp;
> int next_set = 0;
>
> - if (blk_queue_enter(q, true))
> + if (blk_queue_enter(q, BLK_MQ_REQ_NOWAIT | BLK_MQ_REQ_PREEMPT))
> return;
> spin_lock_irqsave(q->queue_lock, flags);
>
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 1c16a247fae6..a3cf36c8079b 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -2926,21 +2926,29 @@ static void scsi_wait_for_queuecommand(struct scsi_device *sdev)
> int
> scsi_device_quiesce(struct scsi_device *sdev)
> {
> + struct request_queue *q = sdev->request_queue;
> int err;
>
> + /* If the SCSI device already has been quiesced, do nothing. */
> + if (blk_set_preempt_only(q))
> + return 0;
This way isn't safe:
1) suppose path1 sets the flag, and blk_mq_freeze_queue() isn't
finished, or even not started;
2) path2 sees the flag set at the exact time, and returns immediately,
and unfortunately SCSI QUIESCE isn't respected in this context.
> +
> + /*
> + * Since blk_mq_freeze_queue() calls synchronize_rcu() indirectly the
> + * effect of blk_set_preempt_only() will be visible for
> + * percpu_ref_tryget() callers that occur after the queue
> + * unfreeze. See also https://lwn.net/Articles/573497/.
> + */
> + blk_mq_freeze_queue(q);
> + blk_mq_unfreeze_queue(q);
This way isn't safe too, because queue may has been frozen before
scsi_device_quiesce() is run, then there isn't synchronize_rcu()
implicated in blk_mq_freeze_queue().
Please take a look at my previous post in the following link:
https://marc.info/?l=linux-block&m=150703957529335&w=2
https://marc.info/?l=linux-kernel&m=150703956929333&w=2
--
Ming
