Provided the device driver does not implement dispatch budget accounting
(which only SCSI does) the loop in __blk_mq_do_dispatch_sched() pulls
requests from the IO scheduler as long as it is willing to give out any.
That defeats scheduling heuristics inside the scheduler by creating
false impression that the device can take more IO when it in fact
cannot.

For example with BFQ IO scheduler on top of virtio-blk device setting
blkio cgroup weight has barely any impact on observed throughput of
async IO because __blk_mq_do_dispatch_sched() always sucks out all the
IO queued in BFQ. BFQ first submits IO from higher weight cgroups but
when that is all dispatched, it will give out IO of lower weight cgroups
as well. And then we have to wait for all this IO to be dispatched to
the disk (which means lot of it actually has to complete) before the
IO scheduler is queried again for dispatching more requests. This
completely destroys any service differentiation.

So grab request tag for a request pulled out of the IO scheduler already
in __blk_mq_do_dispatch_sched() and do not pull any more requests if we
cannot get it because we are unlikely to be able to dispatch it. That
way only single request is going to wait in the dispatch list for some
tag to free.
Reviewed-by: NMing Lei <ming.lei@redhat.com>
Signed-off-by: NJan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20210603104721.6309-1-jack@suse.czSigned-off-by: NJens Axboe <axboe@kernel.dk>

The error handling on a nullb->disk allocation currently jumps to
out_cleanup_disk that calls blk_cleanup_disk with a null pointer causing
a null pointer dereference issue. Fix this by jumping to out_cleanup_tags
instead.

Addresses-Coverity: ("Dereference after null check")
Fixes: 132226b3 ("null_blk: convert to blk_alloc_disk/blk_cleanup_disk")
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Reviewed-by: NChaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20210602100659.11058-1-colin.king@canonical.comSigned-off-by: NJens Axboe <axboe@kernel.dk>

Just opencode the xa_load in the callers, as none of them actually
needs a reference to the bdev.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Reviewed-by: NMing Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20210525061301.2242282-9-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Add a helper to find the dev_t for a disk + partno tuple.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NMing Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20210525061301.2242282-8-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

The bd_part_count value only makes sense for whole devices, so move it
to struct gendisk and give it a more descriptive name.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Reviewed-by: NMing Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20210525061301.2242282-7-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Split __blkdev_put into one helper for the whole device, and one for
partitions as well as another shared helper for flushing the block
device inode mapping.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Reviewed-by: NMing Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20210525061301.2242282-6-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Keep in the callers and thus remove the for_part argument.  This mirrors
what is done on the blkdev_get side and slightly simplifies
blkdev_get_part as well.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NMing Lei <ming.lei@rehat.com>
Link: https://lore.kernel.org/r/20210525061301.2242282-5-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Replace the per-block device bd_mutex with a per-gendisk open_mutex,
thus simplifying locking wherever we deal with partitions.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NMing Lei <ming.lei@redhat.com>
Acked-by: NRoger Pau Monné <roger.pau@citrix.com>
Link: https://lore.kernel.org/r/20210525061301.2242282-4-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Do the early unlocked syncing even earlier to move more code out of
the recursive path.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NMing Lei <ming.lei@redhat.com>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Link: https://lore.kernel.org/r/20210525061301.2242282-3-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Split __blkdev_get into one helper for the whole device, and one for
opening partitions.  This removes the (bounded) recursion when opening
a partition.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NMing Lei <ming.lei@redhat.com>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Link: https://lore.kernel.org/r/20210525061301.2242282-2-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

blk_alloc_queue is just an internal helper now, unexport it and remove
it from the public header.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NUlf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210521055116.1053587-27-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Convert the null_blk driver to use the blk_alloc_disk and blk_cleanup_disk
helpers to simplify gendisk and request_queue allocation.  Note that the
blk-mq mode is left with its own allocations scheme, to be handled later.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NUlf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210521055116.1053587-26-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Convert the xpram driver to use the blk_alloc_disk and blk_cleanup_disk
helpers to simplify gendisk and request_queue allocation.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Reviewed-by: NUlf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210521055116.1053587-25-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Convert the dcssblk driver to use the blk_alloc_disk and blk_cleanup_disk
helpers to simplify gendisk and request_queue allocation.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Reviewed-by: NUlf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210521055116.1053587-24-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Convert the ps3vram driver to use the blk_alloc_disk and blk_cleanup_disk
helpers to simplify gendisk and request_queue allocation.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NUlf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210521055116.1053587-23-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Convert the n64cart driver to use the blk_alloc_disk helper to simplify
gendisk and request_queue allocation.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Reviewed-by: NUlf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210521055116.1053587-22-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Convert the simdisk driver to use the blk_alloc_disk and blk_cleanup_disk
helpers to simplify gendisk and request_queue allocation.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NUlf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210521055116.1053587-21-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Convert the nfblock driver to use the blk_alloc_disk and blk_cleanup_disk
helpers to simplify gendisk and request_queue allocation.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Acked-by: NGeert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Reviewed-by: NUlf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210521055116.1053587-20-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Convert the nvme-multipath driver to use the blk_alloc_disk and
blk_cleanup_disk helpers to simplify gendisk and request_queue
allocation.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NUlf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210521055116.1053587-19-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Convert the nvdimm-pmem driver to use the blk_alloc_disk and
blk_cleanup_disk helpers to simplify gendisk and request_queue
allocation.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NUlf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210521055116.1053587-18-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Convert the nvdimm-btt driver to use the blk_alloc_disk and
blk_cleanup_disk helpers to simplify gendisk and request_queue
allocation.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Reviewed-by: NUlf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210521055116.1053587-17-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Convert the nvdimm-blk driver to use the blk_alloc_disk and
blk_cleanup_disk helpers to simplify gendisk and request_queue
allocation.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NUlf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210521055116.1053587-16-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Convert the md driver to use the blk_alloc_disk and blk_cleanup_disk
helpers to simplify gendisk and request_queue allocation.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Reviewed-by: NUlf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210521055116.1053587-15-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Convert the dm driver to use the blk_alloc_disk and blk_cleanup_disk
helpers to simplify gendisk and request_queue allocation.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NUlf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210521055116.1053587-14-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Convert the bcache driver to use the blk_alloc_disk and blk_cleanup_disk
helpers to simplify gendisk and request_queue allocation.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Acked-by: NColy Li <colyli@suse.de>
Reviewed-by: NUlf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210521055116.1053587-13-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Convert the lightnvm driver to use the blk_alloc_disk and blk_cleanup_disk
helpers to simplify gendisk and request_queue allocation.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NUlf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210521055116.1053587-12-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Convert the zram driver to use the blk_alloc_disk and blk_cleanup_disk
helpers to simplify gendisk and request_queue allocation.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NUlf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210521055116.1053587-11-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Convert the rsxx driver to use the blk_alloc_disk and blk_cleanup_disk
helpers to simplify gendisk and request_queue allocation.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NUlf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210521055116.1053587-10-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Convert the pktcdvd driver to use the blk_alloc_disk and blk_cleanup_disk
helpers to simplify gendisk and request_queue allocation.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Reviewed-by: NUlf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210521055116.1053587-9-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Convert the drbd driver to use the blk_alloc_disk and blk_cleanup_disk
helpers to simplify gendisk and request_queue allocation.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Reviewed-by: NUlf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210521055116.1053587-8-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Convert the brd driver to use the blk_alloc_disk and blk_cleanup_disk
helpers to simplify gendisk and request_queue allocation.  This also
allows to remove the request_queue pointer in struct request_queue,
and to simplify the initialization as blk_cleanup_disk can be called
on any disk returned from blk_alloc_disk.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Reviewed-by: NUlf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210521055116.1053587-7-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Add two new APIs to allocate and free a gendisk including the
request_queue for use with BIO based drivers.  This is to avoid
boilerplate code in drivers.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Reviewed-by: NUlf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210521055116.1053587-6-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Add a flag to indicate that __device_add_disk did grab a queue reference
so that disk_release only drops it if we actually had it.  This sort
out one of the major pitfals with partially initialized gendisk that
a lot of drivers did get wrong or still do.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Reviewed-by: NLuis Chamberlain <mcgrof@kernel.org>
Reviewed-by: NUlf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210521055116.1053587-5-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Automatically set the GENHD_FL_EXT_DEVT flag for all disks allocated
without an explicit number of minors.  This is what all new block
drivers should do, so make sure it is the default without boilerplate
code.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Reviewed-by: NLuis Chamberlain <mcgrof@kernel.org>
Reviewed-by: NUlf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210521055116.1053587-4-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Keep this together with the first place that actually looks at
->minors and prepare for not passing a minors argument to
alloc_disk.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Reviewed-by: NLuis Chamberlain <mcgrof@kernel.org>
Reviewed-by: NUlf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210521055116.1053587-3-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

Untangle the mess around blk_alloc_devt by moving the check for
the used allocation scheme into the callers.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Reviewed-by: NLuis Chamberlain <mcgrof@kernel.org>
Reviewed-by: NUlf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210521055116.1053587-2-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

The tags used for an IO scheduler are currently per hctx.

As such, when q->nr_hw_queues grows, so does the request queue total IO
scheduler tag depth.

This may cause problems for SCSI MQ HBAs whose total driver depth is
fixed.

Ming and Yanhui report higher CPU usage and lower throughput in scenarios
where the fixed total driver tag depth is appreciably lower than the total
scheduler tag depth:
https://lore.kernel.org/linux-block/440dfcfc-1a2c-bd98-1161-cec4d78c6dfc@huawei.com/T/#mc0d6d4f95275a2743d1c8c3e4dc9ff6c9aa3a76b

In that scenario, since the scheduler tag is got first, much contention
is introduced since a driver tag may not be available after we have got
the sched tag.

Improve this scenario by introducing request queue-wide tags for when
a tagset-wide sbitmap is used. The static sched requests are still
allocated per hctx, as requests are initialised per hctx, as in
blk_mq_init_request(..., hctx_idx, ...) ->
set->ops->init_request(.., hctx_idx, ...).

For simplicity of resizing the request queue sbitmap when updating the
request queue depth, just init at the max possible size, so we don't need
to deal with the possibly with swapping out a new sbitmap for old if
we need to grow.
Signed-off-by: NJohn Garry <john.garry@huawei.com>
Reviewed-by: NMing Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/1620907258-30910-3-git-send-email-john.garry@huawei.comSigned-off-by: NJens Axboe <axboe@kernel.dk>

The tag allocation code to alloc the sbitmap pairs is common for regular
bitmaps tags and shared sbitmap, so refactor into a common function.

Also remove superfluous "flags" argument from blk_mq_init_shared_sbitmap().
Signed-off-by: NJohn Garry <john.garry@huawei.com>
Reviewed-by: NMing Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/1620907258-30910-2-git-send-email-john.garry@huawei.comSigned-off-by: NJens Axboe <axboe@kernel.dk>

Before we free request queue, clearing flush request reference in
tags->rqs[], so that potential UAF can be avoided.

Based on one patch written by David Jeffery.
Tested-by: NJohn Garry <john.garry@huawei.com>
Reviewed-by: NBart Van Assche <bvanassche@acm.org>
Reviewed-by: NDavid Jeffery <djeffery@redhat.com>
Signed-off-by: NMing Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20210511152236.763464-5-ming.lei@redhat.comSigned-off-by: NJens Axboe <axboe@kernel.dk>

refcount_inc_not_zero() in bt_tags_iter() still may read one freed
request.

Fix the issue by the following approach:

1) hold a per-tags spinlock when reading ->rqs[tag] and calling
refcount_inc_not_zero in bt_tags_iter()

2) clearing stale request referred via ->rqs[tag] before freeing
request pool, the per-tags spinlock is held for clearing stale
->rq[tag]

So after we cleared stale requests, bt_tags_iter() won't observe
freed request any more, also the clearing will wait for pending
request reference.

The idea of clearing ->rqs[] is borrowed from John Garry's previous
patch and one recent David's patch.
Tested-by: NJohn Garry <john.garry@huawei.com>
Reviewed-by: NDavid Jeffery <djeffery@redhat.com>
Reviewed-by: NBart Van Assche <bvanassche@acm.org>
Signed-off-by: NMing Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20210511152236.763464-4-ming.lei@redhat.comSigned-off-by: NJens Axboe <axboe@kernel.dk>