This patch adds 'blk_mq_ctx' parameter to blk_get_flush_queue(),
so that this function can find the corresponding blk_flush_queue
bound with current mq context since the flush queue will become
per hw-queue.

For legacy queue, the parameter can be simply 'NULL'.

For multiqueue case, the parameter should be set as the context
from which the related request is originated. With this context
info, the hw queue and related flush queue can be found easily.
Signed-off-by: NMing Lei <ming.lei@canonical.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

Just figuring out flush queue at the entry of kicking off flush
machinery and request's completion handler, then pass it through.
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NMing Lei <ming.lei@canonical.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

Now mission of the two helpers is over, and just call
blk_alloc_flush_queue() and blk_free_flush_queue() directly.
Signed-off-by: NMing Lei <ming.lei@canonical.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

This patch introduces 'struct blk_flush_queue' and puts all
flush machinery related fields into this structure, so that

	- flush implementation details aren't exposed to driver
	- it is easy to convert to per dispatch-queue flush machinery

This patch is basically a mechanical replacement.
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NMing Lei <ming.lei@canonical.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

This patch trys to use local variable to access flush request,
so that we can convert to per-queue flush machinery a bit easier.
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NMing Lei <ming.lei@canonical.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

These fields are always used with the flush request, so
initialize them together.
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NMing Lei <ming.lei@canonical.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

These two temporary functions are introduced for holding flush
initialization and de-initialization, so that we can
introduce 'flush queue' easier in the following patch. And
once 'flush queue' and its allocation/free functions are ready,
they will be removed for sake of code readability.
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NMing Lei <ming.lei@canonical.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

It is reasonable to allocate flush req in blk_mq_init_flush().
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NMing Lei <ming.lei@canonical.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

Failure of initializing one hctx isn't handled, so this patch
introduces blk_mq_init_hctx() and its pair to handle it explicitly.
Also this patch makes code cleaner.
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NMing Lei <ming.lei@canonical.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

Signed-off-by: NChristoph Hellwig <hch@lst.de>

Moved blk_mq_rq_timed_out() definition to the private blk-mq.h header.
Signed-off-by: NJens Axboe <axboe@fb.com>

Commit 8cb34819cdd5d(blk-mq: unshared timeout handler) introduces
blk-mq's own timeout handler, and removes following line:

	blk_queue_rq_timed_out(q, blk_mq_rq_timed_out);

which then causes blk_add_timer() to bypass adding the timer,
since blk-mq no longer has q->rq_timed_out_fn defined.

This patch fixes the problem by bypassing the check for blk-mq,
so that both request deadlines are still set and the rolling
timer updated.
Signed-off-by: NMing Lei <ming.lei@canonical.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

It's not uncommon for crash dump kernels to be limited to 128MB or
something low in that area. This is normally not a problem for
devices as we don't use that much memory, but for some shared SCSI
setups with huge queue depths, it can potentially fill most of
memory with tons of request allocations. blk-mq does scale back
when it fails to allocate memory, but it scales back just enough
so that blk-mq succeeds. This could still leave the system with
not enough memory to make any real progress.

Check if we are in a kdump environment and limit the hardware
queues and tag depth.
Signed-off-by: NJens Axboe <axboe@fb.com>

This patch removes two unnecessary blk_clear_rq_complete(),
the REQ_ATOM_COMPLETE flag is cleared inside blk_mq_start_request(),
so:

	- The blk_clear_rq_complete() in blk_flush_restore_request()
	needn't because the request will be freed later, and clearing
	it here may open a small race window with timeout.

	- The blk_clear_rq_complete() in blk_mq_requeue_request() isn't
	necessary too, even though REQ_ATOM_STARTED is cleared in
	__blk_mq_requeue_request(), in theory it still may cause a small
	race window with timeout since the two clear_bit() may be
	reordered.
Signed-off-by: NMing Lei <ming.lei@canoical.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

Allow blk-mq to pass an argument to the timeout handler to indicate
if we're timing out a reserved or regular command.  For many drivers
those need to be handled different.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@fb.com>

Duplicate the (small) timeout handler in blk-mq so that we can pass
arguments more easily to the driver timeout handler.  This enables
the next patch.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@fb.com>

Don't do a kmalloc from timer to handle timeouts, chances are we could be
under heavy load or similar and thus just miss out on the timeouts.
Fortunately it is very easy to just iterate over all in use tags, and doing
this properly actually cleans up the blk_mq_busy_iter API as well, and
prepares us for the next patch by passing a reserved argument to the
iterator.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@fb.com>

Now that we've changed the driver API on the submission side use the
opportunity to fix up the name on the completion side to fit into the
general scheme.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@fb.com>

When we call blk_mq_start_request from the core blk-mq code before calling into
->queue_rq there is a racy window where the timeout handler can hit before we've
fully set up the driver specific part of the command.

Move the call to blk_mq_start_request into the driver so the driver can start
the request only once it is fully set up.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@fb.com>

Pass an explicit parameter for the last request in a batch to ->queue_rq
instead of using a request flag.  Besides being a cleaner and non-stateful
interface this is also required for the next patch, which fixes the blk-mq
I/O submission code to not start a time too early.
Signed-off-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>

When a queue is registered, the block layer turns off the bypass
setting (because bypass is enabled when the queue is created).  This
doesn't work well for queues that are unregistered and then registered
again; we get a WARNING because of the unbalanced calls to
blk_queue_bypass_end().

This patch fixes the problem by making blk_register_queue() call
blk_queue_bypass_end() only the first time the queue is registered.
Signed-off-by: NAlan Stern <stern@rowland.harvard.edu>
Acked-by: NTejun Heo <tj@kernel.org>
CC: James Bottomley <James.Bottomley@HansenPartnership.com>
CC: Jens Axboe <axboe@kernel.dk>
Signed-off-by: NJens Axboe <axboe@fb.com>

bdev_get_queue() returns the request_queue associated with the
specified block_device.  blk_get_backing_dev_info() makes use of
bdev_get_queue() to determine the associated bdi given a block_device.

All the callers of bdev_get_queue() including
blk_get_backing_dev_info() assume that bdev_get_queue() may return
NULL and implement NULL handling; however, bdev_get_queue() requires
the passed in block_device is opened and attached to its gendisk.
Because an active gendisk always has a valid request_queue associated
with it, bdev_get_queue() can never return NULL and neither can
blk_get_backing_dev_info().

Make it clear that neither of the two functions can return NULL and
remove NULL handling from all the callers.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Chris Mason <clm@fb.com>
Cc: Dave Chinner <david@fromorbit.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

blkcg->id is a unique id given to each blkcg; however, the
cgroup_subsys_state which each blkcg embeds already has ->serial_nr
which can be used for the same purpose.  Drop blkcg->id and replace
its uses with blkcg->css.serial_nr.  Rename cfq_cgroup->blkcg_id to
->blkcg_serial_nr and @id in check_blkcg_changed() to @serial_nr for
consistency.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NVivek Goyal <vgoyal@redhat.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

Releases the dev_t minor when all references are closed to prevent
another device from acquiring the same major/minor.

Since the partition's release may be invoked from call_rcu's soft-irq
context, the ext_dev_idr's mutex had to be replaced with a spinlock so
as not so sleep.
Signed-off-by: NKeith Busch <keith.busch@intel.com>
Cc: stable@kernel.org
Signed-off-by: NJens Axboe <axboe@fb.com>

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>

QUEUE_FLAG_NO_SG_MERGE is set at default for blk-mq devices,
so bio->bi_phys_segment computed may be bigger than
queue_max_segments(q) for blk-mq devices, then drivers will
fail to handle the case, for example, BUG_ON() in
virtio_queue_rq() can be triggerd for virtio-blk:

	https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1359146

This patch fixes the issue by ignoring the QUEUE_FLAG_NO_SG_MERGE
flag if the computed bio->bi_phys_segment is bigger than
queue_max_segments(q), and the regression is caused by commit
05f1dd53(block: add queue flag for disabling SG merging).
Reported-by: NKick In <pierre-andre.morey@canonical.com>
Tested-by: NChris J Arges <chris.j.arges@canonical.com>
Signed-off-by: NMing Lei <ming.lei@canonical.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

Dan writes:

block/bsg.c:327 bsg_map_hdr() error: 'next_rq' dereferencing possible
ERR_PTR().

Fix this by setting next_rq to NULL, for the case where it can be
!= NULL but an error pointer.
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

The blk_get_request function may fail in low-memory conditions or during
device removal (even if __GFP_WAIT is set). To distinguish between these
errors, modify the blk_get_request call stack to return the appropriate
ERR_PTR. Verify that all callers check the return status and consider
IS_ERR instead of a simple NULL pointer check.

For consistency, make a similar change to the blk_mq_alloc_request leg
of blk_get_request.  It may fail if the queue is dead, or the caller was
unwilling to wait.
Signed-off-by: NJoe Lawrence <joe.lawrence@stratus.com>
Acked-by: Jiri Kosina <jkosina@suse.cz> [for pktdvd]
Acked-by: Boaz Harrosh <bharrosh@panasas.com> [for osd]
Reviewed-by: NJeff Moyer <jmoyer@redhat.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

Explain that weight has to be updated on activation.
This complements previous fix e15693ef ("cfq-iosched: Fix wrong
children_weight calculation").
Signed-off-by: NToshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
Signed-off-by: NJens Axboe <axboe@fb.com>

The blk-core dead queue checks introduce an error scenario to
blk_get_request that returns NULL if the request queue has been
shutdown. This affects the behavior for __GFP_WAIT callers, who should
verify the return value before dereferencing.
Signed-off-by: NJoe Lawrence <joe.lawrence@stratus.com>
Acked-by: Jiri Kosina <jkosina@suse.cz> [for pktdvd]
Reviewed-by: NJeff Moyer <jmoyer@redhat.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

cfq_group_service_tree_add() is applying new_weight at the beginning of
the function via cfq_update_group_weight().
This actually allows weight to change between adding it to and subtracting
it from children_weight, and triggers WARN_ON_ONCE() in
cfq_group_service_tree_del(), or even causes oops by divide error during
vfr calculation in cfq_group_service_tree_add().

The detailed scenario is as follows:
1. Create blkio cgroups X and Y as a child of X.
   Set X's weight to 500 and perform some I/O to apply new_weight.
   This X's I/O completes before starting Y's I/O.
2. Y starts I/O and cfq_group_service_tree_add() is called with Y.
3. cfq_group_service_tree_add() walks up the tree during children_weight
   calculation and adds parent X's weight (500) to children_weight of root.
   children_weight becomes 500.
4. Set X's weight to 1000.
5. X starts I/O and cfq_group_service_tree_add() is called with X.
6. cfq_group_service_tree_add() applies its new_weight (1000).
7. I/O of Y completes and cfq_group_service_tree_del() is called with Y.
8. I/O of X completes and cfq_group_service_tree_del() is called with X.
9. cfq_group_service_tree_del() subtracts X's weight (1000) from
   children_weight of root. children_weight becomes -500.
   This triggers WARN_ON_ONCE().
10. Set X's weight to 500.
11. X starts I/O and cfq_group_service_tree_add() is called with X.
12. cfq_group_service_tree_add() applies its new_weight (500) and adds it
    to children_weight of root. children_weight becomes 0. Calcularion of
    vfr triggers oops by divide error.

weight should be updated right before adding it to children_weight.
Reported-by: NRuki Sekiya <sekiya.ruki@lab.ntt.co.jp>
Signed-off-by: NToshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
Acked-by: NTejun Heo <tj@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: NJens Axboe <axboe@fb.com>

Before commit 2cada584 ("block: cleanup error handling in sg_io"),
we had ret = 0 before entering the last big if block of sg_io.

Since 2cada584, ret = -EFAULT, which breaks hdparm:

/dev/sda:
 setting Advanced Power Management level to 0xc8 (200)
 HDIO_DRIVE_CMD failed: Bad address
 APM_level      = 128
Signed-off-by: NSabrina Dubroca <sd@queasysnail.net>
Fixes: 2cada584 ("block: cleanup error handling in sg_io")
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@fb.com>

blk_rq_set_block_pc() memsets rq->cmd to 0, so it should come
immediately after blk_get_request() to avoid overwriting the
user-supplied CDB.  Also check for failure to allocate rq.

Fixes: f27b087b ("block: add blk_rq_set_block_pc()")
Cc: <stable@vger.kernel.org> # 3.16.x
Signed-off-by: NTony Battersby <tonyb@cybernetics.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>

Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NBoaz Harrosh <boaz@plexistor.com>
Signed-off-by: NJens Axboe <axboe@fb.com>