This reverts commit 6d4d2735.

bfq.limit_depth passes word_depths[] as shallow_depth down to sbitmap core
sbitmap_get_shallow, which uses just the number to limit the scan depth of
each bitmap word, formula:
scan_percentage_for_each_word = shallow_depth / (1 << sbimap->shift) * 100%

That means the comments's percentiles 50%, 75%, 18%, 37% of bfq are correct.
But after commit patch 'bfq: Fix computation of shallow depth', we use
sbitmap.depth instead, as a example in following case:

sbitmap.depth = 256, map_nr = 4, shift = 6; sbitmap_word.depth = 64.
The resulsts of computed bfqd->word_depths[] are {128, 192, 48, 96}, and
three of the numbers exceed core dirver's 'sbitmap_word.depth=64' limit
nothing.
Signed-off-by: NLin Feng <linf@wangsu.com>
Reviewed-by: NJan Kara <jack@suse.cz>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Currently whenever bfq queue has a request queued we add now -
last_completion_time to the think time statistics. This is however
misleading in case the process is able to submit several requests in
parallel because e.g. if the queue has request completed at time T0 and
then queues new requests at times T1, T2, then we will add T1-T0 and
T2-T0 to think time statistics which just doesn't make any sence (the
queue's think time is penalized by the queue being able to submit more
IO). So add to think time statistics only time intervals when the queue
had no IO pending.
Signed-off-by: NJan Kara <jack@suse.cz>
Acked-by: NPaolo Valente <paolo.valente@linaro.org>
[axboe: fix whitespace on empty line]
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Use local variable 'ttime' instead of dereferencing bfqq.
Signed-off-by: NJan Kara <jack@suse.cz>
Acked-by: NPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

bfq_setup_cooperator() uses bfqd->in_serv_last_pos so detect whether it
makes sense to merge current bfq queue with the in-service queue.
However if the in-service queue is freshly scheduled and didn't dispatch
any requests yet, bfqd->in_serv_last_pos is stale and contains value
from the previously scheduled bfq queue which can thus result in a bogus
decision that the two queues should be merged. This bug can be observed
for example with the following fio jobfile:

[global]
direct=0
ioengine=sync
invalidate=1
size=1g
rw=read

[reader]
numjobs=4
directory=/mnt

where the 4 processes will end up in the one shared bfq queue although
they do IO to physically very distant files (for some reason I was able to
observe this only with slice_idle=1ms setting).

Fix the problem by invalidating bfqd->in_serv_last_pos when switching
in-service queue.

Fixes: 058fdecc ("block, bfq: fix in-service-queue check for queue merging")
CC: stable@vger.kernel.org
Signed-off-by: NJan Kara <jack@suse.cz>
Acked-by: NPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

It's only used in the same file, mark is appropriately static.

Fixes: 71217df3 ("block, bfq: make waker-queue detection more robust")
Reported-by: Nkernel test robot <lkp@intel.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

In the presence of many parallel I/O flows, the detection of waker
bfq_queues suffers from false positives. This commits addresses this
issue by making the filtering of actual wakers more selective. In more
detail, a candidate waker must be found to meet waker requirements
three times before being promoted to actual waker.
Tested-by: NJan Kara <jack@suse.cz>
Signed-off-by: NPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

To prevent injection information from being lost on bfq_queue merging,
also the amount of service that a bfq_queue receives must be saved and
restored when the bfq_queue is merged and split, respectively.
Tested-by: NJan Kara <jack@suse.cz>
Signed-off-by: NPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

To prevent weight-raising information from being lost on bfq_queue merging,
also the amount of service that a bfq_queue receives must be saved and
restored when the bfq_queue is merged and split, respectively.
Tested-by: NJan Kara <jack@suse.cz>
Signed-off-by: NPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

A bfq_queue may happen to be deemed as soft real-time while it is
still enjoying interactive weight-raising. If this happens because of
a false positive, then the bfq_queue is likely to loose its soft
real-time status soon. Upon losing such a status, the bfq_queue must
get back its interactive weight-raising, if its interactive period is
not over yet. But this case is not handled. This commit corrects this
error.
Tested-by: NJan Kara <jack@suse.cz>
Signed-off-by: NPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Upon an I/O-dispatch attempt, BFQ may detect that it was better to
plug I/O dispatch, and to wait for a new request to arrive for the
currently in-service queue. But the arrival of a new request for an
empty bfq_queue, and thus the switch from idle to busy of the
bfq_queue, may cause the scenario to change, and make plugging no
longer needed for service guarantees, or more convenient for
throughput. In this case, keeping I/O-dispatch plugged would certainly
lower throughput.

To address this issue, this commit makes such a check, and stops
plugging I/O if it is better to stop plugging I/O.
Tested-by: NJan Kara <jack@suse.cz>
Signed-off-by: NPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Some BFQ mechanisms make their decisions on a bfq_queue basing also on
whether the bfq_queue is I/O bound. In this respect, the current logic
for evaluating whether a bfq_queue is I/O bound is rather rough. This
commits replaces this logic with a more effective one.

The new logic measures the percentage of time during which a bfq_queue
is active, and marks the bfq_queue as I/O bound if the latter if this
percentage is above a fixed threshold.
Tested-by: NJan Kara <jack@suse.cz>
Signed-off-by: NPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

This reverts commit b445547e.

Since both mq-deadline and BFQ completely ignore hctx they are passed to
their dispatch function and dispatch whatever request they deem fit
checking whether any request for a particular hctx is queued is just
pointless since we'll very likely get a request from a different hctx
anyway. In the following commit we'll deal with lock contention in these
IO schedulers in presence of multiple HW queues in a different way.
Signed-off-by: NJan Kara <jack@suse.cz>
Reviewed-by: NMing Lei <ming.lei@redhat.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

This commits preserves I/O-dispatch plugging for a special symmetric
case that may suddenly turn into asymmetric: the case where only one
bfq_queue, say bfqq, is busy. In this case, not expiring bfqq does not
cause any harm to any other queues in terms of service guarantees. In
contrast, it avoids the following unlucky sequence of events: (1) bfqq
is expired, (2) a new queue with a lower weight than bfqq becomes busy
(or more queues), (3) the new queue is served until a new request
arrives for bfqq, (4) when bfqq is finally served, there are so many
requests of the new queue in the drive that the pending requests for
bfqq take a lot of time to be served. In particular, event (2) may
case even already dispatched requests of bfqq to be delayed, inside
the drive. So, to avoid this series of events, the scenario is
preventively declared as asymmetric also if bfqq is the only busy
queues. By doing so, I/O-dispatch plugging is performed for bfqq.
Tested-by: NJan Kara <jack@suse.cz>
Signed-off-by: NPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

BFQ tags some bfq_queues as interactive or soft_rt if it deems that
these bfq_queues contain the I/O of, respectively, interactive or soft
real-time applications. BFQ privileges both these special types of
bfq_queues over normal bfq_queues. To privilege a bfq_queue, BFQ
mainly raises the weight of the bfq_queue. In particular, soft_rt
bfq_queues get a higher weight than interactive bfq_queues.

A bfq_queue may turn from interactive to soft_rt. And this leads to a
tricky issue. Soft real-time applications usually start with an
I/O-bound, interactive phase, in which they load themselves into main
memory. BFQ correctly detects this phase, and keeps the bfq_queues
associated with the application in interactive mode for a
while. Problems arise when the I/O pattern of the application finally
switches to soft real-time. One of the conditions for a bfq_queue to
be deemed as soft_rt is that the bfq_queue does not consume too much
bandwidth. But the bfq_queues associated with a soft real-time
application consume as much bandwidth as they can in the loading phase
of the application. So, after the application becomes truly soft
real-time, a lot of time should pass before the average bandwidth
consumed by its bfq_queues finally drops to a value acceptable for
soft_rt bfq_queues. As a consequence, there might be a time gap during
which the application is not privileged at all, because its bfq_queues
are not interactive any longer, but cannot be deemed as soft_rt yet.

To avoid this problem, BFQ pretends that an interactive bfq_queue
consumes zero bandwidth, and allows an interactive bfq_queue to switch
to soft_rt. Yet, this fake zero-bandwidth consumption easily causes
the bfq_queue to often switch to soft_rt deceptively, during its
loading phase. As in soft_rt mode, the bfq_queue gets its bandwidth
correctly computed, and therefore soon switches back to
interactive. Then it switches again to soft_rt, and so on. These
spurious fluctuations usually cause losses of throughput, because they
deceive BFQ's mechanisms for boosting throughput (injection,
I/O-plugging avoidance, ...).

This commit addresses this issue as follows:
1) It does compute actual bandwidth consumption also for interactive
   bfq_queues. This avoids the above false positives.
2) When a bfq_queue switches from interactive to normal mode, the
   consumed bandwidth is reset (forgotten). This allows the
   bfq_queue to enjoy soft_rt very quickly. In particular, two
   alternatives are possible in this switch:
    - the bfq_queue still has backlog, and therefore there is a budget
      already scheduled to serve the bfq_queue; in this case, the
      scheduling of the current budget of the bfq_queue is not
      hindered, because only the scheduling of the next budget will
      be affected by the weight drop. After that, if the bfq_queue is
      actually in a soft_rt phase, and becomes empty during the
      service of its current budget, which is the natural behavior of
      a soft_rt bfq_queue, then the bfq_queue will be considered as
      soft_rt when its next I/O arrives. If, in contrast, the
      bfq_queue remains constantly non-empty, then its next budget
      will be scheduled with a low weight, which is the natural
      treatment for an I/O-bound (non soft_rt) bfq_queue.
    - the bfq_queue is empty; in this case, the bfq_queue may be
      considered unjustly soft_rt when its new I/O arrives. Yet
      the problem is now much smaller than before, because it is
      unlikely that more than one spurious fluctuation occurs.
Tested-by: NJan Kara <jack@suse.cz>
Signed-off-by: NPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

BFQ heuristics try to detect interactive I/O, and raise the weight of
the queues containing such an I/O. Yet, if also the user changes the
weight of a queue (i.e., the user changes the ioprio of the process
associated with that queue), then it is most likely better to prevent
BFQ heuristics from silently changing the same weight.
Tested-by: NJan Kara <jack@suse.cz>
Signed-off-by: NPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Tests on slower machines showed current window to be way too
small. This commit increases it.
Tested-by: NJan Kara <jack@suse.cz>
Signed-off-by: NPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Since commit c5089591c3ba ("block, bfq: detect wakers and
unconditionally inject their I/O"), when the in-service bfq_queue, say
Q, is temporarily empty, BFQ checks whether there are I/O requests to
inject (also) from the waker bfq_queue for Q. To this goal, the value
pointed by bfqq->waker_bfqq->next_rq must be controlled. However, the
current implementation mistakenly looks at bfqq->next_rq, which
instead points to the next request of the currently served queue.

This mistake evidently causes losses of throughput in scenarios with
waker bfq_queues.

This commit corrects this mistake.

Fixes: c5089591c3ba ("block, bfq: detect wakers and unconditionally inject their I/O")
Signed-off-by: NJia Cheng Hu <jia.jiachenghu@gmail.com>
Signed-off-by: NJan Kara <jack@suse.cz>
Signed-off-by: NPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

The value of the I/O plugging (idling) timeout is used also as the
think-time threshold to decide whether a process has a short think
time.  In this respect, a good value of this timeout for rotational
drives is un the order of several ms. Yet, this is often too long a
time interval to be effective as a think-time threshold. This commit
mitigates this problem (by a lot, according to tests), by halving the
threshold.
Tested-by: NJan Kara <jack@suse.cz>
Signed-off-by: NPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

BFQ computes number of tags it allows to be allocated for each request type
based on tag bitmap. However it uses 1 << bitmap.shift as number of
available tags which is wrong. 'shift' is just an internal bitmap value
containing logarithm of how many bits bitmap uses in each bitmap word.
Thus number of tags allowed for some request types can be far to low.
Use proper bitmap.depth which has the number of tags instead.
Signed-off-by: NJan Kara <jack@suse.cz>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Yang Yang reported the following crash caused by requeueing a flush
request in Kyber:

  [    2.517297] Unable to handle kernel paging request at virtual address ffffffd8071c0b00
  ...
  [    2.517468] pc : clear_bit+0x18/0x2c
  [    2.517502] lr : sbitmap_queue_clear+0x40/0x228
  [    2.517503] sp : ffffff800832bc60 pstate : 00c00145
  ...
  [    2.517599] Process ksoftirqd/5 (pid: 51, stack limit = 0xffffff8008328000)
  [    2.517602] Call trace:
  [    2.517606]  clear_bit+0x18/0x2c
  [    2.517619]  kyber_finish_request+0x74/0x80
  [    2.517627]  blk_mq_requeue_request+0x3c/0xc0
  [    2.517637]  __scsi_queue_insert+0x11c/0x148
  [    2.517640]  scsi_softirq_done+0x114/0x130
  [    2.517643]  blk_done_softirq+0x7c/0xb0
  [    2.517651]  __do_softirq+0x208/0x3bc
  [    2.517657]  run_ksoftirqd+0x34/0x60
  [    2.517663]  smpboot_thread_fn+0x1c4/0x2c0
  [    2.517667]  kthread+0x110/0x120
  [    2.517669]  ret_from_fork+0x10/0x18

This happens because Kyber doesn't track flush requests, so
kyber_finish_request() reads a garbage domain token. Only call the
scheduler's requeue_request() hook if RQF_ELVPRIV is set (like we do for
the finish_request() hook in blk_mq_free_request()). Now that we're
handling it in blk-mq, also remove the check from BFQ.
Reported-by: NYang Yang <yang.yang@vivo.com>
Signed-off-by: NOmar Sandoval <osandov@fb.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

High CPU utilization on "native_queued_spin_lock_slowpath" due to lock
contention is possible for mq-deadline and bfq IO schedulers
when nr_hw_queues is more than one.

It is because kblockd work queue can submit IO from all online CPUs
(through blk_mq_run_hw_queues()) even though only one hctx has pending
commands.

The elevator callback .has_work for mq-deadline and bfq scheduler considers
pending work if there are any IOs on request queue but it does not account
hctx context.

Add a per-hctx 'elevator_queued' count to the hctx to avoid triggering
the elevator even though there are no requests queued.

[jpg: Relocated atomic_dec() in dd_dispatch_request(), update commit message per Kashyap]
Signed-off-by: NKashyap Desai <kashyap.desai@broadcom.com>
Signed-off-by: NHannes Reinecke <hare@suse.de>
Signed-off-by: NJohn Garry <john.garry@huawei.com>
Tested-by: NDouglas Gilbert <dgilbert@interlog.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Introduce pointers for the blk_mq_tags regular and reserved bitmap tags,
with the goal of later being able to use a common shared tag bitmap across
all HW contexts in a set.
Signed-off-by: NJohn Garry <john.garry@huawei.com>
Tested-by: Don Brace<don.brace@microsemi.com> #SCSI resv cmds patches used
Tested-by: NDouglas Gilbert <dgilbert@interlog.com>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Replace the existing /* fall through */ comments and its variants with
the new pseudo-keyword macro fallthrough[1]. Also, remove unnecessary
fall-through markings when it is the case.

[1] https://www.kernel.org/doc/html/v5.7/process/deprecated.html?highlight=fallthrough#implicit-switch-case-fall-throughSigned-off-by: NGustavo A. R. Silva <gustavoars@kernel.org>

Change "at at" to "at a".
Signed-off-by: NRandy Dunlap <rdunlap@infradead.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: linux-block@vger.kernel.org
Signed-off-by: NJens Axboe <axboe@kernel.dk>

None of the I/O schedulers actually needs it.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NMing Lei <ming.lei@redhat.com>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: NBart Van Assche <bvanassche@acm.org>
Reviewed-by: NDaniel Wagner <dwagner@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Use the common interface bdi_dev_name() to get device name.
Signed-off-by: NYufen Yu <yuyufen@huawei.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: NJan Kara <jack@suse.cz>
Reviewed-by: NBart Van Assche <bvanassche@acm.org>

Add missing <linux/backing-dev.h> include BFQ
Signed-off-by: NJens Axboe <axboe@kernel.dk>

A bfq_put_queue() may be invoked in __bfq_bic_change_cgroup(). The
goal of this put is to release a process reference to a bfq_queue. But
process-reference releases may trigger also some extra operation, and,
to this goal, are handled through bfq_release_process_ref(). So, turn
the invocation of bfq_put_queue() into an invocation of
bfq_release_process_ref().

Tested-by: cki-project@redhat.com
Signed-off-by: NPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

In bfq_idle_slice_timer func, bfqq = bfqd->in_service_queue is
not in bfqd-lock critical section. The bfqq, which is not
equal to NULL in bfq_idle_slice_timer, may be freed after passing
to bfq_idle_slice_timer_body. So we will access the freed memory.

In addition, considering the bfqq may be in race, we should
firstly check whether bfqq is in service before doing something
on it in bfq_idle_slice_timer_body func. If the bfqq in race is
not in service, it means the bfqq has been expired through
__bfq_bfqq_expire func, and wait_request flags has been cleared in
__bfq_bfqd_reset_in_service func. So we do not need to re-clear the
wait_request of bfqq which is not in service.

KASAN log is given as follows:
[13058.354613] ==================================================================
[13058.354640] BUG: KASAN: use-after-free in bfq_idle_slice_timer+0xac/0x290
[13058.354644] Read of size 8 at addr ffffa02cf3e63f78 by task fork13/19767
[13058.354646]
[13058.354655] CPU: 96 PID: 19767 Comm: fork13
[13058.354661] Call trace:
[13058.354667]  dump_backtrace+0x0/0x310
[13058.354672]  show_stack+0x28/0x38
[13058.354681]  dump_stack+0xd8/0x108
[13058.354687]  print_address_description+0x68/0x2d0
[13058.354690]  kasan_report+0x124/0x2e0
[13058.354697]  __asan_load8+0x88/0xb0
[13058.354702]  bfq_idle_slice_timer+0xac/0x290
[13058.354707]  __hrtimer_run_queues+0x298/0x8b8
[13058.354710]  hrtimer_interrupt+0x1b8/0x678
[13058.354716]  arch_timer_handler_phys+0x4c/0x78
[13058.354722]  handle_percpu_devid_irq+0xf0/0x558
[13058.354731]  generic_handle_irq+0x50/0x70
[13058.354735]  __handle_domain_irq+0x94/0x110
[13058.354739]  gic_handle_irq+0x8c/0x1b0
[13058.354742]  el1_irq+0xb8/0x140
[13058.354748]  do_wp_page+0x260/0xe28
[13058.354752]  __handle_mm_fault+0x8ec/0x9b0
[13058.354756]  handle_mm_fault+0x280/0x460
[13058.354762]  do_page_fault+0x3ec/0x890
[13058.354765]  do_mem_abort+0xc0/0x1b0
[13058.354768]  el0_da+0x24/0x28
[13058.354770]
[13058.354773] Allocated by task 19731:
[13058.354780]  kasan_kmalloc+0xe0/0x190
[13058.354784]  kasan_slab_alloc+0x14/0x20
[13058.354788]  kmem_cache_alloc_node+0x130/0x440
[13058.354793]  bfq_get_queue+0x138/0x858
[13058.354797]  bfq_get_bfqq_handle_split+0xd4/0x328
[13058.354801]  bfq_init_rq+0x1f4/0x1180
[13058.354806]  bfq_insert_requests+0x264/0x1c98
[13058.354811]  blk_mq_sched_insert_requests+0x1c4/0x488
[13058.354818]  blk_mq_flush_plug_list+0x2d4/0x6e0
[13058.354826]  blk_flush_plug_list+0x230/0x548
[13058.354830]  blk_finish_plug+0x60/0x80
[13058.354838]  read_pages+0xec/0x2c0
[13058.354842]  __do_page_cache_readahead+0x374/0x438
[13058.354846]  ondemand_readahead+0x24c/0x6b0
[13058.354851]  page_cache_sync_readahead+0x17c/0x2f8
[13058.354858]  generic_file_buffered_read+0x588/0xc58
[13058.354862]  generic_file_read_iter+0x1b4/0x278
[13058.354965]  ext4_file_read_iter+0xa8/0x1d8 [ext4]
[13058.354972]  __vfs_read+0x238/0x320
[13058.354976]  vfs_read+0xbc/0x1c0
[13058.354980]  ksys_read+0xdc/0x1b8
[13058.354984]  __arm64_sys_read+0x50/0x60
[13058.354990]  el0_svc_common+0xb4/0x1d8
[13058.354994]  el0_svc_handler+0x50/0xa8
[13058.354998]  el0_svc+0x8/0xc
[13058.354999]
[13058.355001] Freed by task 19731:
[13058.355007]  __kasan_slab_free+0x120/0x228
[13058.355010]  kasan_slab_free+0x10/0x18
[13058.355014]  kmem_cache_free+0x288/0x3f0
[13058.355018]  bfq_put_queue+0x134/0x208
[13058.355022]  bfq_exit_icq_bfqq+0x164/0x348
[13058.355026]  bfq_exit_icq+0x28/0x40
[13058.355030]  ioc_exit_icq+0xa0/0x150
[13058.355035]  put_io_context_active+0x250/0x438
[13058.355038]  exit_io_context+0xd0/0x138
[13058.355045]  do_exit+0x734/0xc58
[13058.355050]  do_group_exit+0x78/0x220
[13058.355054]  __wake_up_parent+0x0/0x50
[13058.355058]  el0_svc_common+0xb4/0x1d8
[13058.355062]  el0_svc_handler+0x50/0xa8
[13058.355066]  el0_svc+0x8/0xc
[13058.355067]
[13058.355071] The buggy address belongs to the object at ffffa02cf3e63e70#012 which belongs to the cache bfq_queue of size 464
[13058.355075] The buggy address is located 264 bytes inside of#012 464-byte region [ffffa02cf3e63e70, ffffa02cf3e64040)
[13058.355077] The buggy address belongs to the page:
[13058.355083] page:ffff7e80b3cf9800 count:1 mapcount:0 mapping:ffff802db5c90780 index:0xffffa02cf3e606f0 compound_mapcount: 0
[13058.366175] flags: 0x2ffffe0000008100(slab|head)
[13058.370781] raw: 2ffffe0000008100 ffff7e80b53b1408 ffffa02d730c1c90 ffff802db5c90780
[13058.370787] raw: ffffa02cf3e606f0 0000000000370023 00000001ffffffff 0000000000000000
[13058.370789] page dumped because: kasan: bad access detected
[13058.370791]
[13058.370792] Memory state around the buggy address:
[13058.370797]  ffffa02cf3e63e00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fb fb
[13058.370801]  ffffa02cf3e63e80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[13058.370805] >ffffa02cf3e63f00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[13058.370808]                                                                 ^
[13058.370811]  ffffa02cf3e63f80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[13058.370815]  ffffa02cf3e64000: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
[13058.370817] ==================================================================
[13058.370820] Disabling lock debugging due to kernel taint

Here, we directly pass the bfqd to bfq_idle_slice_timer_body func.
--
V2->V3: rewrite the comment as suggested by Paolo Valente
V1->V2: add one comment, and add Fixes and Reported-by tag.

Fixes: aee69d78 ("block, bfq: introduce the BFQ-v0 I/O scheduler as an extra scheduler")
Acked-by: NPaolo Valente <paolo.valente@linaro.org>
Reported-by: NWang Wang <wangwang2@huawei.com>
Signed-off-by: NZhiqiang Liu <liuzhiqiang26@huawei.com>
Signed-off-by: NFeilong Lin <linfeilong@huawei.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

The exact, general goal of the function bfq_split_bfqq() is not that
apparent. Add a comment to make it clear.
Tested-by: NOleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: NPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

ifdefs around gets and puts of bfq groups reduce readability, remove them.
Tested-by: NOleksandr Natalenko <oleksandr@natalenko.name>
Reported-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

The flag on_st in the bfq_entity data structure is true if the entity
is on a service tree or is in service. Yet the name of the field,
confusingly, does not mention the second, very important case. Extend
the name to mention the second case too.
Tested-by: NOleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: NPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

BFQ maintains an ordered list, implemented with an RB tree, of
head-request positions of non-empty bfq_queues. This position tree,
inherited from CFQ, is used to find bfq_queues that contain I/O close
to each other. BFQ merges these bfq_queues into a single shared queue,
if this boosts throughput on the device at hand.

There is however a special-purpose bfq_queue that does not participate
in queue merging, the oom bfq_queue. Yet, also this bfq_queue could be
wrongly added to the position tree. So bfqq_find_close() could return
the oom bfq_queue, which is a source of further troubles in an
out-of-memory situation. This commit prevents the oom bfq_queue from
being inserted into the position tree.
Tested-by: NPatrick Dung <patdung100@gmail.com>
Tested-by: NOleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: NPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Commit 478de338 ("block, bfq: deschedule empty bfq_queues not
referred by any process") fixed commit 3726112e ("block, bfq:
re-schedule empty queues if they deserve I/O plugging") by
descheduling an empty bfq_queue when it remains with not process
reference. Yet, this still left a case uncovered: an empty bfq_queue
with not process reference that remains in service. This happens for
an in-service sync bfq_queue that is deemed to deserve I/O-dispatch
plugging when it remains empty. Yet no new requests will arrive for
such a bfq_queue if no process sends requests to it any longer. Even
worse, the bfq_queue may happen to be prematurely freed while still in
service (because there may remain no reference to it any longer).

This commit solves this problem by preventing I/O dispatch from being
plugged for the in-service bfq_queue, if the latter has no process
reference (the bfq_queue is then prevented from remaining in service).

Fixes: 3726112e ("block, bfq: re-schedule empty queues if they deserve I/O plugging")
Tested-by: NOleksandr Natalenko <oleksandr@natalenko.name>
Reported-by: NPatrick Dung <patdung100@gmail.com>
Tested-by: NPatrick Dung <patdung100@gmail.com>
Signed-off-by: NPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

This macro is never used after introduced from commit aee69d78
("block, bfq: introduce the BFQ-v0 I/O scheduler as an extra scheduler")

Better to remove it.
Signed-off-by: NAlex Shi <alex.shi@linux.alibaba.com>
Cc: Paolo Valente <paolo.valente@linaro.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: linux-block@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Since commit 3726112e ("block, bfq: re-schedule empty queues if
they deserve I/O plugging"), to prevent the service guarantees of a
bfq_queue from being violated, the bfq_queue may be left busy, i.e.,
scheduled for service, even if empty (see comments in
__bfq_bfqq_expire() for details). But, if no process will send
requests to the bfq_queue any longer, then there is no point in
keeping the bfq_queue scheduled for service.

In addition, keeping the bfq_queue scheduled for service, but with no
process reference any longer, may cause the bfq_queue to be freed when
descheduled from service. But this is assumed to never happen, and
causes a UAF if it happens. This, in turn, caused crashes [1, 2].

This commit fixes this issue by descheduling an empty bfq_queue when
it remains with not process reference.

[1] https://bugzilla.redhat.com/show_bug.cgi?id=1767539
[2] https://bugzilla.kernel.org/show_bug.cgi?id=205447

Fixes: 3726112e ("block, bfq: re-schedule empty queues if they deserve I/O plugging")
Reported-by: NChris Evich <cevich@redhat.com>
Reported-by: NPatrick Dung <patdung100@gmail.com>
Reported-by: NThorsten Schubert <tschubert@bafh.org>
Tested-by: NThorsten Schubert <tschubert@bafh.org>
Tested-by: NOleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: NPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

When used on cgroup1, bfq uses the blkg->stat_bytes and ->stat_ios
from blk-cgroup core to populate six stat knobs.  blk-cgroup core is
moving away from blkg_rwstat to improve scalability and won't be able
to support this usage.

It isn't like the sharing gains all that much.  Let's break it out to
dedicated rwstat counters which are updated when on cgroup1.  This
makes use of bfqg_*rwstat*() helpers outside of
CONFIG_BFQ_CGROUP_DEBUG.  Move them out.

v2: Compile fix when !CONFIG_BFQ_CGROUP_DEBUG.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

If equal to 0, the injection limit for a bfq_queue is pushed to 1
after a first sample of the total service time of the I/O requests of
the queue is computed (to allow injection to start). Yet, because of a
mistake in the branch that performs this action, the push may happen
also in some other case. This commit fixes this issue.
Tested-by: NOleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: NPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

The update period of the injection limit has been tentatively set to
100 ms, to reduce fluctuations. This value however proved to cause,
occasionally, the limit to be decremented for some bfq_queue only
after the queue underwent excessive injection for a lot of time. This
commit reduces the period to 10 ms.
Tested-by: NOleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: NPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Upon an increment attempt of the injection limit, the latter is
constrained not to become higher than twice the maximum number
max_rq_in_driver of I/O requests that have happened to be in service
in the drive. This high bound allows the injection limit to grow
beyond max_rq_in_driver, which may then cause max_rq_in_driver itself
to grow.

However, since the limit is incremented by only one unit at a time,
there is no need for such a high bound, and just max_rq_in_driver+1 is
enough.
Tested-by: NOleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: NPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

BFQ updates the injection limit of each bfq_queue as a function of how
much the limit inflates the service times experienced by the I/O
requests of the queue. So only service times affected by injection
must be taken into account. Unfortunately, in the current
implementation of this update scheme, the service time of an I/O
request rq not affected by injection may happen to be considered in
the following case: there is no I/O request in service when rq
arrives.

This commit fixes this issue by making sure that only service times
affected by injection are considered for updating the injection
limit. In particular, the service time of an I/O request rq is now
considered only if at least one of the following two conditions holds:
- the destination bfq_queue for rq underwent injection before rq
arrival, and there is still I/O in service in the drive on rq arrival
(the service of such unfinished I/O may delay the service of rq);
- injection occurs between the arrival and the completion time of rq.
Tested-by: NOleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: NPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>