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    Subject[PATCH block/for-linus 1/2] block: separate out blk_rq_merge_ok() and blk_try_merge() from elevator functions
    blk_rq_merge_ok() is the elevator-neutral part of merge eligibility
    test. blk_try_merge() determines merge direction and expects the
    caller to have tested elv_rq_merge_ok() previously.

    elv_rq_merge_ok() now wraps blk_rq_merge_ok() and then calls
    elv_iosched_allow_merge(). elv_try_merge() is removed and the two
    callers are updated to call elv_rq_merge_ok() explicitly followed by
    blk_try_merge(). While at it, make rq_merge_ok() functions return
    bool.

    This is to prepare for plug merge update and doesn't introduce any
    behavior change.

    This is based on Jens' patch to skip elevator_allow_merge_fn() from
    plug merge.

    Signed-off-by: Tejun Heo <tj@kernel.org>
    LKML-Reference: <4F16F3CA.90904@kernel.dk>
    Original-patch-by: Jens Axboe <axboe@kernel.dk>
    ---
    Jens, these two patches fix the easy-to-trigger oops on elevator
    switch bug. These are based on your previous patch.

    Thanks.

    block/blk-core.c | 4 +--
    block/blk-merge.c | 37 +++++++++++++++++++++++++++++++
    block/blk.h | 2 +
    block/elevator.c | 55 +++--------------------------------------------
    include/linux/elevator.h | 3 --
    5 files changed, 46 insertions(+), 55 deletions(-)

    Index: work/block/blk-merge.c
    ===================================================================
    --- work.orig/block/blk-merge.c
    +++ work/block/blk-merge.c
    @@ -471,3 +471,40 @@ int blk_attempt_req_merge(struct request
    {
    return attempt_merge(q, rq, next);
    }
    +
    +bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
    +{
    + if (!rq_mergeable(rq))
    + return false;
    +
    + /* don't merge file system requests and discard requests */
    + if ((bio->bi_rw & REQ_DISCARD) != (rq->bio->bi_rw & REQ_DISCARD))
    + return false;
    +
    + /* don't merge discard requests and secure discard requests */
    + if ((bio->bi_rw & REQ_SECURE) != (rq->bio->bi_rw & REQ_SECURE))
    + return false;
    +
    + /* different data direction or already started, don't merge */
    + if (bio_data_dir(bio) != rq_data_dir(rq))
    + return false;
    +
    + /* must be same device and not a special request */
    + if (rq->rq_disk != bio->bi_bdev->bd_disk || rq->special)
    + return false;
    +
    + /* only merge integrity protected bio into ditto rq */
    + if (bio_integrity(bio) != blk_integrity_rq(rq))
    + return false;
    +
    + return true;
    +}
    +
    +int blk_try_merge(struct request *rq, struct bio *bio)
    +{
    + if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_sector)
    + return ELEVATOR_BACK_MERGE;
    + else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_sector)
    + return ELEVATOR_FRONT_MERGE;
    + return ELEVATOR_NO_MERGE;
    +}
    Index: work/block/blk.h
    ===================================================================
    --- work.orig/block/blk.h
    +++ work/block/blk.h
    @@ -137,6 +137,8 @@ int blk_attempt_req_merge(struct request
    struct request *next);
    void blk_recalc_rq_segments(struct request *rq);
    void blk_rq_set_mixed_merge(struct request *rq);
    +bool blk_rq_merge_ok(struct request *rq, struct bio *bio);
    +int blk_try_merge(struct request *rq, struct bio *bio);

    void blk_queue_congestion_threshold(struct request_queue *q);

    Index: work/block/elevator.c
    ===================================================================
    --- work.orig/block/elevator.c
    +++ work/block/elevator.c
    @@ -70,39 +70,9 @@ static int elv_iosched_allow_merge(struc
    /*
    * can we safely merge with this request?
    */
    -int elv_rq_merge_ok(struct request *rq, struct bio *bio)
    +bool elv_rq_merge_ok(struct request *rq, struct bio *bio)
    {
    - if (!rq_mergeable(rq))
    - return 0;
    -
    - /*
    - * Don't merge file system requests and discard requests
    - */
    - if ((bio->bi_rw & REQ_DISCARD) != (rq->bio->bi_rw & REQ_DISCARD))
    - return 0;
    -
    - /*
    - * Don't merge discard requests and secure discard requests
    - */
    - if ((bio->bi_rw & REQ_SECURE) != (rq->bio->bi_rw & REQ_SECURE))
    - return 0;
    -
    - /*
    - * different data direction or already started, don't merge
    - */
    - if (bio_data_dir(bio) != rq_data_dir(rq))
    - return 0;
    -
    - /*
    - * must be same device and not a special request
    - */
    - if (rq->rq_disk != bio->bi_bdev->bd_disk || rq->special)
    - return 0;
    -
    - /*
    - * only merge integrity protected bio into ditto rq
    - */
    - if (bio_integrity(bio) != blk_integrity_rq(rq))
    + if (!blk_rq_merge_ok(rq, bio))
    return 0;

    if (!elv_iosched_allow_merge(rq, bio))
    @@ -112,23 +82,6 @@ int elv_rq_merge_ok(struct request *rq,
    }
    EXPORT_SYMBOL(elv_rq_merge_ok);

    -int elv_try_merge(struct request *__rq, struct bio *bio)
    -{
    - int ret = ELEVATOR_NO_MERGE;
    -
    - /*
    - * we can merge and sequence is ok, check if it's possible
    - */
    - if (elv_rq_merge_ok(__rq, bio)) {
    - if (blk_rq_pos(__rq) + blk_rq_sectors(__rq) == bio->bi_sector)
    - ret = ELEVATOR_BACK_MERGE;
    - else if (blk_rq_pos(__rq) - bio_sectors(bio) == bio->bi_sector)
    - ret = ELEVATOR_FRONT_MERGE;
    - }
    -
    - return ret;
    -}
    -
    static struct elevator_type *elevator_find(const char *name)
    {
    struct elevator_type *e;
    @@ -478,8 +431,8 @@ int elv_merge(struct request_queue *q, s
    /*
    * First try one-hit cache.
    */
    - if (q->last_merge) {
    - ret = elv_try_merge(q->last_merge, bio);
    + if (q->last_merge && elv_rq_merge_ok(q->last_merge, bio)) {
    + ret = blk_try_merge(q->last_merge, bio);
    if (ret != ELEVATOR_NO_MERGE) {
    *req = q->last_merge;
    return ret;
    Index: work/include/linux/elevator.h
    ===================================================================
    --- work.orig/include/linux/elevator.h
    +++ work/include/linux/elevator.h
    @@ -122,7 +122,6 @@ extern void elv_dispatch_add_tail(struct
    extern void elv_add_request(struct request_queue *, struct request *, int);
    extern void __elv_add_request(struct request_queue *, struct request *, int);
    extern int elv_merge(struct request_queue *, struct request **, struct bio *);
    -extern int elv_try_merge(struct request *, struct bio *);
    extern void elv_merge_requests(struct request_queue *, struct request *,
    struct request *);
    extern void elv_merged_request(struct request_queue *, struct request *, int);
    @@ -155,7 +154,7 @@ extern ssize_t elv_iosched_store(struct
    extern int elevator_init(struct request_queue *, char *);
    extern void elevator_exit(struct elevator_queue *);
    extern int elevator_change(struct request_queue *, const char *);
    -extern int elv_rq_merge_ok(struct request *, struct bio *);
    +extern bool elv_rq_merge_ok(struct request *, struct bio *);

    /*
    * Helper functions.
    Index: work/block/blk-core.c
    ===================================================================
    --- work.orig/block/blk-core.c
    +++ work/block/blk-core.c
    @@ -1282,10 +1282,10 @@ static bool attempt_plug_merge(struct re

    (*request_count)++;

    - if (rq->q != q)
    + if (rq->q != q || !elv_rq_merge_ok(rq, bio))
    continue;

    - el_ret = elv_try_merge(rq, bio);
    + el_ret = blk_try_merge(rq, bio);
    if (el_ret == ELEVATOR_BACK_MERGE) {
    ret = bio_attempt_back_merge(q, rq, bio);
    if (ret)

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