blk-mq uses percpu_ref for its usage counter which tracks the number
of in-flight commands and used to synchronously drain the queue on
freeze.  percpu_ref shutdown takes measureable wallclock time as it
involves a sched RCU grace period.  This means that draining a blk-mq
takes measureable wallclock time.  One would think that this shouldn't
matter as queue shutdown should be a rare event which takes place
asynchronously w.r.t. userland.

Unfortunately, SCSI probing involves synchronously setting up and then
tearing down a lot of request_queues back-to-back for non-existent
LUNs.  This means that SCSI probing may take more than ten seconds
when scsi-mq is used.

This will be properly fixed by implementing a mechanism to keep
q->mq_usage_counter in atomic mode till genhd registration; however,
that involves rather big updates to percpu_ref which is difficult to
apply late in the devel cycle (v3.17-rc6 at the moment).  As a
stop-gap measure till the proper fix can be implemented in the next
cycle, this patch introduces __percpu_ref_kill_expedited() and makes
blk_mq_freeze_queue() use it.  This is heavy-handed but should work
for testing the experimental SCSI blk-mq implementation.
Signed-off-by: NTejun Heo <tj@kernel.org>
Reported-by: NChristoph Hellwig <hch@infradead.org>
Link: http://lkml.kernel.org/g/20140919113815.GA10791@lst.de
Fixes: add703fd ("blk-mq: use percpu_ref for mq usage count")
Cc: Kent Overstreet <kmo@daterainc.com>
Cc: Jens Axboe <axboe@kernel.dk>
Tested-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@fb.com>

When requests are retried due to hw or sw resource shortages,
we often stop the associated hardware queue. So ensure that we
restart the queues when running the requeue work, otherwise the
queue run will be a no-op.
Signed-off-by: NJens Axboe <axboe@fb.com>

__blk_mq_alloc_rq_maps() can be invoked multiple times, if we scale
back the queue depth if we are low on memory. So don't clear
set->tags when we fail, this is handled directly in
the parent function, blk_mq_alloc_tag_set().
Reported-by: NRobert Elliott  <Elliott@hp.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

We should not insert requests into the flush state machine from
blk_mq_insert_request.  All incoming flush requests come through
blk_{m,s}q_make_request and are handled there, while blk_execute_rq_nowait
should only be called for BLOCK_PC requests.  All other callers
deal with requests that already went through the flush statemchine
and shouldn't be reinserted into it.
Reported-by: NRobert Elliott  <Elliott@hp.com>
Debugged-by: NMing Lei <ming.lei@canonical.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@fb.com>

This patch should fix the bug reported in
https://lkml.org/lkml/2014/9/11/249.

We have to initialize at least the atomic_flags and the cmd_flags when
allocating storage for the requests.

Otherwise blk_mq_timeout_check() might dereference uninitialized
pointers when racing with the creation of a request.

Also move the reset of cmd_flags for the initializing code to the point
where a request is freed. So we will never end up with pending flush
request indicators that might trigger dereferences of invalid pointers
in blk_mq_timeout_check().

Cc: stable@vger.kernel.org
Signed-off-by: NDavid Hildenbrand <dahi@linux.vnet.ibm.com>
Reported-by: NPaulo De Rezende Pinatti <ppinatti@linux.vnet.ibm.com>
Tested-by: NPaulo De Rezende Pinatti <ppinatti@linux.vnet.ibm.com>
Acked-by: NChristian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

When we start the request, we set the deadline and flip the bits
marking the request as started and non-complete. However, it's
important that the deadline store is ordered before flipping the
bits, otherwise we could have a small window where the request is
marked started but with an invalid deadline. This can confuse the
timeout handling.
Suggested-by: NMing Lei <tom.leiming@gmail.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

If we are running in a kdump environment, resources are scarce.
For some SCSI setups with a huge set of shared tags, we run out
of memory allocating what the drivers is asking for. So implement
a scale back logic to reduce the tag depth for those cases, allowing
the driver to successfully load.

We should extend this to detect low memory situations, and implement
a sane fallback for those (1 queue, 64 tags, or something like that).
Tested-by: NRobert Elliott <elliott@hp.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

Percpu allocator now supports allocation mask.  Add @gfp to
percpu_ref_init() so that !GFP_KERNEL allocation masks can be used
with percpu_refs too.

This patch doesn't make any functional difference.

v2: blk-mq conversion was missing.  Updated.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Kent Overstreet <koverstreet@google.com>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Nicholas A. Bellinger <nab@linux-iscsi.org>
Cc: Jens Axboe <axboe@kernel.dk>

In blk-mq.c blk_mq_alloc_tag_set, if:
	set->tags = kmalloc_node()
succeeds, but one of the blk_mq_init_rq_map() calls fails,
	goto out_unwind;
needs to free set->tags so the caller is not obligated
to do so.  None of the current callers (null_blk,
virtio_blk, virtio_blk, or the forthcoming scsi-mq)
do so.

set->tags needs to be set to NULL after doing so,
so other tag cleanup logic doesn't try to free
a stale pointer later.  Also set it to NULL
in blk_mq_free_tag_set.

Tested with error injection on the forthcoming
scsi-mq + hpsa combination.
Signed-off-by: NRobert Elliott <elliott@hp.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

This patch fixes code such as the following with scsi-mq enabled:

    rq = blk_get_request(...);
    blk_rq_set_block_pc(rq);

    rq->cmd = my_cmd_buffer; /* separate CDB buffer */

    blk_execute_rq_nowait(...);

Code like this appears in e.g. sg_start_req() in drivers/scsi/sg.c (for
large CDBs only).  Without this patch, scsi_mq_prep_fn() will set
rq->cmd back to rq->__cmd, causing the wrong CDB to be sent to the device.
Signed-off-by: NTony Battersby <tonyb@cybernetics.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

While converting to percpu_ref for freezing, add703fd ("blk-mq:
use percpu_ref for mq usage count") incorrectly made
blk_mq_freeze_queue() misbehave when freezing is nested due to
percpu_ref_kill() being invoked on an already killed ref.

Fix it by making blk_mq_freeze_queue() kill and kick the queue only
for the outermost freeze attempt.  All the nested ones can simply wait
for the ref to reach zero.

While at it, remove unnecessary @wake initialization from
blk_mq_unfreeze_queue().
Signed-off-by: NTejun Heo <tj@kernel.org>
Reported-by: NMing Lei <ming.lei@canonical.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

Just grammar or spelling errors, nothing major.
Signed-off-by: NJens Axboe <axboe@fb.com>

blk-mq uses BLK_MQ_F_SHOULD_MERGE, as set by the driver at init time,
to determine whether it should merge IO or not. However, this could
also be disabled by the admin, if merging is switched off through
sysfs. So check the general queue state as well before attempting
to merge IO.
Reported-by: NRob Elliott <Elliott@hp.com>
Tested-by: NRob Elliott <Elliott@hp.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

Before doing queue release, the queue has been freezed already
by blk_cleanup_queue(), so needn't to freeze queue for deleting
tag set.

This patch fixes the WARNING of "percpu_ref_kill() called more than once!"
which is triggered during unloading block driver.

Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: NMing Lei <ming.lei@canonical.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

Currently, blk-mq uses a percpu_counter to keep track of how many
usages are in flight.  The percpu_counter is drained while freezing to
ensure that no usage is left in-flight after freezing is complete.
blk_mq_queue_enter/exit() and blk_mq_[un]freeze_queue() implement this
per-cpu gating mechanism.

This type of code has relatively high chance of subtle bugs which are
extremely difficult to trigger and it's way too hairy to be open coded
in blk-mq.  percpu_ref can serve the same purpose after the recent
changes.  This patch replaces the open-coded per-cpu usage counting
and draining mechanism with percpu_ref.

blk_mq_queue_enter() performs tryget_live on the ref and exit()
performs put.  blk_mq_freeze_queue() kills the ref and waits until the
reference count reaches zero.  blk_mq_unfreeze_queue() revives the ref
and wakes up the waiters.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Nicholas A. Bellinger <nab@linux-iscsi.org>
Cc: Kent Overstreet <kmo@daterainc.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

Keeping __blk_mq_drain_queue() as a separate function doesn't buy us
anything and it's gonna be further simplified.  Let's flatten it into
its caller.

This patch doesn't make any functional change.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Nicholas A. Bellinger <nab@linux-iscsi.org>
Signed-off-by: NJens Axboe <axboe@fb.com>

blk_mq freezing is entangled with generic bypassing which bypasses
blkcg and io scheduler and lets IO requests fall through the block
layer to the drivers in FIFO order.  This allows forward progress on
IOs with the advanced features disabled so that those features can be
configured or altered without worrying about stalling IO which may
lead to deadlock through memory allocation.

However, generic bypassing doesn't quite fit blk-mq.  blk-mq currently
doesn't make use of blkcg or ioscheds and it maps bypssing to
freezing, which blocks request processing and drains all the in-flight
ones.  This causes problems as bypassing assumes that request
processing is online.  blk-mq works around this by conditionally
allowing request processing for the problem case - during queue
initialization.

Another weirdity is that except for during queue cleanup, bypassing
started on the generic side prevents blk-mq from processing new
requests but doesn't drain the in-flight ones.  This shouldn't break
anything but again highlights that something isn't quite right here.

The root cause is conflating blk-mq freezing and generic bypassing
which are two different mechanisms.  The only intersecting purpose
that they serve is during queue cleanup.  Let's properly separate
blk-mq freezing from generic bypassing and simply use it where
necessary.

* request_queue->mq_freeze_depth is added and
  blk_mq_[un]freeze_queue() now operate on this counter instead of
  ->bypass_depth.  The replacement for QUEUE_FLAG_BYPASS isn't added
  but the counter is tested directly.  This will be further updated by
  later changes.

* blk_mq_drain_queue() is dropped and "__" prefix is dropped from
  blk_mq_freeze_queue().  Queue cleanup path now calls
  blk_mq_freeze_queue() directly.

* blk_queue_enter()'s fast path condition is simplified to simply
  check @q->mq_freeze_depth.  Previously, the condition was

	!blk_queue_dying(q) &&
	    (!blk_queue_bypass(q) || !blk_queue_init_done(q))

  mq_freeze_depth is incremented right after dying is set and
  blk_queue_init_done() exception isn't necessary as blk-mq doesn't
  start frozen, which only leaves the blk_queue_bypass() test which
  can be replaced by @q->mq_freeze_depth test.

This change simplifies the code and reduces confusion in the area.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Nicholas A. Bellinger <nab@linux-iscsi.org>
Signed-off-by: NJens Axboe <axboe@fb.com>

Currently, both blk_queue_bypass_start() and blk_mq_freeze_queue()
skip queue draining if bypass_depth was already above zero.  The
assumption is that the one which bumped the bypass_depth should have
performed draining already; however, there's nothing which prevents a
new instance of bypassing/freezing from starting before the previous
one finishes draining.  The current code may allow the later
bypassing/freezing instances to complete while there still are
in-flight requests which haven't finished draining.

Fix it by draining regardless of bypass_depth.  We still skip draining
from blk_queue_bypass_start() while the queue is initializing to avoid
introducing excessive delays during boot.  INIT_DONE setting is moved
above the initial blk_queue_bypass_end() so that bypassing attempts
can't slip inbetween.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Nicholas A. Bellinger <nab@linux-iscsi.org>
Signed-off-by: NJens Axboe <axboe@fb.com>

blk-mq uses a percpu_counter to keep track of how many usages are in
flight.  The percpu_counter is drained while freezing to ensure that
no usage is left in-flight after freezing is complete.

blk_mq_queue_enter/exit() and blk_mq_[un]freeze_queue() implement this
per-cpu gating mechanism; unfortunately, it contains a subtle bug -
smp_wmb() in blk_mq_queue_enter() doesn't prevent prevent the cpu from
fetching @q->bypass_depth before incrementing @q->mq_usage_counter and
if freezing happens inbetween the caller can slip through and freezing
can be complete while there are active users.

Use smp_mb() instead so that bypass_depth and mq_usage_counter
modifications and tests are properly interlocked.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Nicholas A. Bellinger <nab@linux-iscsi.org>
Signed-off-by: NJens Axboe <axboe@fb.com>

Currently it calls __blk_mq_run_hw_queue(), which depends on the
CPU placement being correct. This means it's not possible to call
blk_mq_start_hw_queues(q) from a context that is correct for all
queues, leading to triggering the

WARN_ON(!cpumask_test_cpu(raw_smp_processor_id(), hctx->cpumask));

in __blk_mq_run_hw_queue().
Reported-by: NMing Lei <tom.leiming@gmail.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@fb.com>

If we need to drain a queue we need to run all queues, even if they
are marked stopped to make sure the driver has a chance to error out
on all queued requests.

This fixes surprise removal with scsi-mq.
Reported-by: NBart Van Assche <bvanassche@acm.org>
Tested-by: NBart Van Assche <bvanassche@acm.org>
Signed-off-by: NJens Axboe <axboe@fb.com>

This way will become consistent with non-mq case, also
avoid to update rq->deadline twice for mq.

The comment said: "We do this early, to ensure we are on
the right CPU.", but no percpu stuff is used in blk_add_timer(),
so it isn't necessary. Even when inserting from plug list, there
is no such guarantee at all.
Signed-off-by: NMing Lei <tom.leiming@gmail.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

The blk-mq core only initializes this if io stats are enabled, since
blk-mq only reads the field in that case. But drivers could
potentially use it internally, so ensure that we always set it to
the current time when the request is allocated.
Reported-by: NMing Lei <tom.leiming@gmail.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

It'll be used in blk_mq_start_request() to set a potential timeout
for the request, so clear it to zero at alloc time to ensure that
we know if someone has set it or not.

Fixes random early timeouts on NVMe testing.
Signed-off-by: NJens Axboe <axboe@fb.com>

If the queue is going away, don't let new allocs or queueing
happen on it. Go through the normal wait process, and exit with
ENODEV in that case.
Signed-off-by: NKeith Busch <keith.busch@intel.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

For some scsi-mq cases, the tag map can be huge. So increase the
max number of tags we support.

Additionally, don't fail with EINVAL if a user requests too many
tags. Warn that the tag depth has been adjusted down, and store
the new value inside the tag_set passed in.
Signed-off-by: NJens Axboe <axboe@fb.com>

We currently pass in the hardware queue, and get the tags from there.
But from scsi-mq, with a shared tag space, it's a lot more convenient
to pass in the blk_mq_tags instead as the hardware queue isn't always
directly available. So instead of having to re-map to a given
hardware queue from rq->mq_ctx, just pass in the tags structure.
Signed-off-by: NJens Axboe <axboe@fb.com>

When the code was collapsed to avoid duplication, the recent patch
for ensuring that a queue is idled before free was dropped, which was
added by commit 19c5d84f.

Add back the blk_mq_tag_idle(), to ensure we don't leak a reference
to an active queue when it is freed.
Signed-off-by: NJens Axboe <axboe@fb.com>

blk_mq_map_request() can return NULL if we fail entering the queue
(dying, or removed), in which case it has already ended IO on the
bio. So nothing more to do, except just return.
Signed-off-by: NJens Axboe <axboe@fb.com>

'struct blk_mq_ctx' is  __percpu, so add the annotation
and fix the sparse warning reported from Fengguang:

	[block:for-linus 2/3] block/blk-mq.h:75:16: sparse: incorrect
	type in initializer (different address spaces)
Reported-by: Nkbuild test robot <fengguang.wu@intel.com>
Signed-off-by: NMing Lei <tom.leiming@gmail.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

blk_mq_put_ctx() has to be called before io_schedule() in
bt_get().

This patch fixes the problem by taking similar approach from
percpu_ida allocation for the situation.
Signed-off-by: NMing Lei <tom.leiming@gmail.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

The blk-mq tag code need these helpers.
Signed-off-by: NMing Lei <tom.leiming@gmail.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

We have callers outside of the blk-mq proper (like timeouts) that
want to call __blk_mq_complete_request(), so rename the function
and put the decision code for whether to use ->softirq_done_fn
or blk_mq_endio() into __blk_mq_complete_request().

This also makes the interface more logical again.
blk_mq_complete_request() attempts to atomically mark the request
completed, and calls __blk_mq_complete_request() if successful.
__blk_mq_complete_request() then just ends the request.
Signed-off-by: NJens Axboe <axboe@fb.com>

Commit 07068d5b added a direct-to-hw-queue mode, but this mode
needs to remember to add the request timeout handler as well.
Without it, we don't track timeouts for these requests.
Signed-off-by: NJens Axboe <axboe@fb.com>

Currently blk-mq registers all the hardware queues in sysfs,
regardless of whether it uses them (e.g. they have CPU mappings)
or not. The unused hardware queues lack the cpux/ directories,
and the other sysfs entries (like active, pending, etc) are all
zeroes.

Change this so that sysfs correctly reflects the current mappings
of the hardware queues.
Signed-off-by: NJens Axboe <axboe@fb.com>

flush request is special, which borrows the tag from the parent
request. Hence blk_mq_tag_to_rq needs special handling to return
the flush request from the tag.
Signed-off-by: NShaohua Li <shli@fusionio.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

We currently clear a lot more than we need to, so make that a bit
more clever. Make some of the init dependent on features, like
only setting start_time if we are going to use it.
Signed-off-by: NJens Axboe <axboe@fb.com>

If devices are not SG starved, we waste a lot of time potentially
collapsing SG segments. Enough that 1.5% of the CPU time goes
to this, at only 400K IOPS. Add a queue flag, QUEUE_FLAG_NO_SG_MERGE,
which just returns the number of vectors in a bio instead of looping
over all segments and checking for collapsible ones.

Add a BLK_MQ_F_SG_MERGE flag so that drivers can opt-in on the sg
merging, if they so desire.
Signed-off-by: NJens Axboe <axboe@fb.com>

There is no need for drivers to control hardware context allocation
now that we do the context to node mapping in common code.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@fb.com>