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    Subject[PATCH 06/10] block: reorganize queue draining
    Date
    Reorganize queue draining related code in preparation of queue exit
    changes.

    * Factor out actual draining from elv_quiesce_start() to
    blk_drain_queue().

    * Make elv_quiesce_start/end() responsible for their own locking.

    * Replace open-coded ELVSWITCH clearing in elevator_switch() with
    elv_quiesce_end().

    This patch doesn't cause any visible functional difference.

    Signed-off-by: Tejun Heo <tj@kernel.org>
    Cc: Jens Axboe <axboe@kernel.dk>
    ---
    block/blk-core.c | 28 ++++++++++++++++++++++++++++
    block/blk.h | 1 +
    block/elevator.c | 37 +++++++++++--------------------------
    3 files changed, 40 insertions(+), 26 deletions(-)

    diff --git a/block/blk-core.c b/block/blk-core.c
    index fafa669..50e3144 100644
    --- a/block/blk-core.c
    +++ b/block/blk-core.c
    @@ -28,6 +28,7 @@
    #include <linux/task_io_accounting_ops.h>
    #include <linux/fault-inject.h>
    #include <linux/list_sort.h>
    +#include <linux/delay.h>

    #define CREATE_TRACE_POINTS
    #include <trace/events/block.h>
    @@ -345,6 +346,33 @@ void blk_put_queue(struct request_queue *q)
    }
    EXPORT_SYMBOL(blk_put_queue);

    +/**
    + * blk_drain_queue - drain requests from request_queue
    + * @q: queue to drain
    + *
    + * Drain ELV_PRIV requests from @q. The caller is responsible for ensuring
    + * that no new requests which need to be drained are queued.
    + */
    +void blk_drain_queue(struct request_queue *q)
    +{
    + while (true) {
    + int nr_rqs;
    +
    + spin_lock_irq(q->queue_lock);
    +
    + elv_drain_elevator(q);
    +
    + __blk_run_queue(q);
    + nr_rqs = q->rq.elvpriv;
    +
    + spin_unlock_irq(q->queue_lock);
    +
    + if (!nr_rqs)
    + break;
    + msleep(10);
    + }
    +}
    +
    /*
    * Note: If a driver supplied the queue lock, it should not zap that lock
    * unexpectedly as some queue cleanup components like elevator_exit() and
    diff --git a/block/blk.h b/block/blk.h
    index da247ba..2b66dc2 100644
    --- a/block/blk.h
    +++ b/block/blk.h
    @@ -15,6 +15,7 @@ void blk_rq_bio_prep(struct request_queue *q, struct request *rq,
    struct bio *bio);
    int blk_rq_append_bio(struct request_queue *q, struct request *rq,
    struct bio *bio);
    +void blk_drain_queue(struct request_queue *q);
    void blk_dequeue_request(struct request *rq);
    void __blk_queue_free_tags(struct request_queue *q);
    bool __blk_end_bidi_request(struct request *rq, int error,
    diff --git a/block/elevator.c b/block/elevator.c
    index cb332cb..74a277f 100644
    --- a/block/elevator.c
    +++ b/block/elevator.c
    @@ -31,7 +31,6 @@
    #include <linux/slab.h>
    #include <linux/init.h>
    #include <linux/compiler.h>
    -#include <linux/delay.h>
    #include <linux/blktrace_api.h>
    #include <linux/hash.h>
    #include <linux/uaccess.h>
    @@ -606,43 +605,35 @@ void elv_requeue_request(struct request_queue *q, struct request *rq)
    void elv_drain_elevator(struct request_queue *q)
    {
    static int printed;
    +
    + lockdep_assert_held(q->queue_lock);
    +
    while (q->elevator->ops->elevator_dispatch_fn(q, 1))
    ;
    - if (q->nr_sorted == 0)
    - return;
    - if (printed++ < 10) {
    + if (q->nr_sorted && printed++ < 10) {
    printk(KERN_ERR "%s: forced dispatching is broken "
    "(nr_sorted=%u), please report this\n",
    q->elevator->elevator_type->elevator_name, q->nr_sorted);
    }
    }

    -/*
    - * Call with queue lock held, interrupts disabled
    - */
    void elv_quiesce_start(struct request_queue *q)
    {
    if (!q->elevator)
    return;

    + spin_lock_irq(q->queue_lock);
    queue_flag_set(QUEUE_FLAG_ELVSWITCH, q);
    + spin_unlock_irq(q->queue_lock);

    - /*
    - * make sure we don't have any requests in flight
    - */
    - elv_drain_elevator(q);
    - while (q->rq.elvpriv) {
    - __blk_run_queue(q);
    - spin_unlock_irq(q->queue_lock);
    - msleep(10);
    - spin_lock_irq(q->queue_lock);
    - elv_drain_elevator(q);
    - }
    + blk_drain_queue(q);
    }

    void elv_quiesce_end(struct request_queue *q)
    {
    + spin_lock_irq(q->queue_lock);
    queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
    + spin_unlock_irq(q->queue_lock);
    }

    void __elv_add_request(struct request_queue *q, struct request *rq, int where)
    @@ -972,7 +963,6 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
    /*
    * Turn on BYPASS and drain all requests w/ elevator private data
    */
    - spin_lock_irq(q->queue_lock);
    elv_quiesce_start(q);

    /*
    @@ -983,8 +973,8 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
    /*
    * attach and start new elevator
    */
    + spin_lock_irq(q->queue_lock);
    elevator_attach(q, e, data);
    -
    spin_unlock_irq(q->queue_lock);

    if (old_elevator->registered) {
    @@ -999,9 +989,7 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
    * finally exit old elevator and turn off BYPASS.
    */
    elevator_exit(old_elevator);
    - spin_lock_irq(q->queue_lock);
    elv_quiesce_end(q);
    - spin_unlock_irq(q->queue_lock);

    blk_add_trace_msg(q, "elv switch: %s", e->elevator_type->elevator_name);

    @@ -1015,10 +1003,7 @@ fail_register:
    elevator_exit(e);
    q->elevator = old_elevator;
    elv_register_queue(q);
    -
    - spin_lock_irq(q->queue_lock);
    - queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
    - spin_unlock_irq(q->queue_lock);
    + elv_quiesce_end(q);

    return err;
    }
    --
    1.7.3.1


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