Most of icq management is about to be moved out of cfq into blk-ioc.
This patch prepares for it.

* Move cfqd->icq_list to request_queue->icq_list

* Make request explicitly point to icq instead of through elevator
  private data.  ->elevator_private[3] is replaced with sub struct elv
  which contains icq pointer and priv[2].  cfq is updated accordingly.

* Meaningless clearing of ->elevator_private[0] removed from
  elv_set_request().  At that point in code, the field was guaranteed
  to be %NULL anyway.

This patch doesn't introduce any functional change.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Currently io_context and cfq logics are mixed without clear boundary.
Most of io_context is independent from cfq but cfq_io_context handling
logic is dispersed between generic ioc code and cfq.

cfq_io_context represents association between an io_context and a
request_queue, which is a concept useful outside of cfq, but it also
contains fields which are useful only to cfq.

This patch takes out generic part and put it into io_cq (io
context-queue) and the rest into cfq_io_cq (cic moniker remains the
same) which contains io_cq.  The following changes are made together.

* cfq_ttime and cfq_io_cq now live in cfq-iosched.c.

* All related fields, functions and constants are renamed accordingly.

* ioc->ioc_data is now "struct io_cq *" instead of "void *" and
  renamed to icq_hint.

This prepares for io_context API cleanup.  Documentation is currently
sparse.  It will be added later.

Changes in this patch are mechanical and don't cause functional
change.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

elevator_queue->ops points to the same ops struct ->elevator_type.ops
is pointing to.  The only effect of caching it in elevator_queue is
shorter notation - it doesn't save any indirect derefence.

Relocate elevator_type->list which used only during module init/exit
to the end of the structure, rename elevator_queue->elevator_type to
->type, and replace elevator_queue->ops with elevator_queue->type.ops.

This doesn't introduce any functional difference.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Elevator switch sequence first attached the new elevator, then tried
registering it (sysfs) and if that failed attached back the old
elevator.  However, sysfs registration doesn't require the elevator to
be attached, so there is no reason to do the "detach, attach new,
register, maybe re-attach old" sequence.  It can just do "register,
detach, attach".

* elevator_init_queue() is updated to set ->elevator_data directly and
  return 0 / -errno.  This allows elevator_exit() on an unattached
  elevator.

* __elv_unregister_queue() which was necessary to unregister
  unattached q is removed in favor of __elv_register_queue() which can
  register unattached q.

* elevator_attach() becomes a single assignment and obscures more then
  it helps.  Dropped.

This will help cleaning up io_context handling across elevator switch.

This patch doesn't introduce visible behavior change.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

When called under queue_lock, current_io_context() triggers lockdep
warning if it hits allocation path.  This is because io_context
installation is protected by task_lock which is not IRQ safe, so it
triggers irq-unsafe-lock -> irq -> irq-safe-lock -> irq-unsafe-lock
deadlock warning.

Given the restriction, accessor + creator rolled into one doesn't work
too well.  Drop current_io_context() and let the users access
task->io_context directly inside queue_lock combined with explicit
creation using create_io_context().

Future ioc updates will further consolidate ioc access and the create
interface will be unexported.

While at it, relocate ioc internal interface declarations in blk.h and
add section comments before and after.

This patch does not introduce functional change.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Now that lazy paths are removed, cfqd_dead_key() is meaningless and
cic->q can be used whereever cic->key is used.  Kill cic->key.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Now that cic's are immediately unlinked under both locks, there's no
need to count and drain cic's before module unload.  RCU callback
completion is waited with rcu_barrier().

While at it, remove residual RCU operations on cic_list.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Now that all cic's are immediately unlinked from both ioc and queue,
lazy dropping from lookup path and trimming on elevator unregister are
unnecessary.  Kill them and remove now unused elevator_ops->trim().

This also leaves call_for_each_cic() without any user.  Removed.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

cic is association between io_context and request_queue.  A cic is
linked from both ioc and q and should be destroyed when either one
goes away.  As ioc and q both have their own locks, locking becomes a
bit complex - both orders work for removal from one but not from the
other.

Currently, cfq tries to circumvent this locking order issue with RCU.
ioc->lock nests inside queue_lock but the radix tree and cic's are
also protected by RCU allowing either side to walk their lists without
grabbing lock.

This rather unconventional use of RCU quickly devolves into extremely
fragile convolution.  e.g. The following is from cfqd going away too
soon after ioc and q exits raced.

 general protection fault: 0000 [#1] PREEMPT SMP
 CPU 2
 Modules linked in:
 [   88.503444]
 Pid: 599, comm: hexdump Not tainted 3.1.0-rc10-work+ #158 Bochs Bochs
 RIP: 0010:[<ffffffff81397628>]  [<ffffffff81397628>] cfq_exit_single_io_context+0x58/0xf0
 ...
 Call Trace:
  [<ffffffff81395a4a>] call_for_each_cic+0x5a/0x90
  [<ffffffff81395ab5>] cfq_exit_io_context+0x15/0x20
  [<ffffffff81389130>] exit_io_context+0x100/0x140
  [<ffffffff81098a29>] do_exit+0x579/0x850
  [<ffffffff81098d5b>] do_group_exit+0x5b/0xd0
  [<ffffffff81098de7>] sys_exit_group+0x17/0x20
  [<ffffffff81b02f2b>] system_call_fastpath+0x16/0x1b

The only real hot path here is cic lookup during request
initialization and avoiding extra locking requires very confined use
of RCU.  This patch makes cic removal from both ioc and request_queue
perform double-locking and unlink immediately.

* From q side, the change is almost trivial as ioc->lock nests inside
  queue_lock.  It just needs to grab each ioc->lock as it walks
  cic_list and unlink it.

* From ioc side, it's a bit more difficult because of inversed lock
  order.  ioc needs its lock to walk its cic_list but can't grab the
  matching queue_lock and needs to perform unlock-relock dancing.

  Unlinking is now wholly done from put_io_context() and fast path is
  optimized by using the queue_lock the caller already holds, which is
  by far the most common case.  If the ioc accessed multiple devices,
  it tries with trylock.  In unlikely cases of fast path failure, it
  falls back to full double-locking dance from workqueue.

Double-locking isn't the prettiest thing in the world but it's *far*
simpler and more understandable than RCU trick without adding any
meaningful overhead.

This still leaves a lot of now unnecessary RCU logics.  Future patches
will trim them.

-v2: Vivek pointed out that cic->q was being dereferenced after
     cic->release() was called.  Updated to use local variable @this_q
     instead.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

* cfq_cic_lookup() may be called without queue_lock and multiple tasks
  can execute it simultaneously for the same shared ioc.  Nothing
  prevents them racing each other and trying to drop the same dead cic
  entry multiple times.

* smp_wmb() in cfq_exit_cic() doesn't really do anything and nothing
  prevents cfq_cic_lookup() seeing stale cic->key.  This usually
  doesn't blow up because by the time cic is exited, all requests have
  been drained and new requests are terminated before going through
  elevator.  However, it can still be triggered by plug merge path
  which doesn't grab queue_lock and thus can't check DEAD state
  reliably.

This patch updates lookup locking such that,

* Lookup is always performed under queue_lock.  This doesn't add any
  more locking.  The only issue is cfq_allow_merge() which can be
  called from plug merge path without holding any lock.  For now, this
  is worked around by using cic of the request to merge into, which is
  guaranteed to have the same ioc.  For longer term, I think it would
  be best to separate out plug merge method from regular one.

* Spurious ioc->lock locking around cic lookup hint assignment
  dropped.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

cfq_get_io_context() would fail if multiple tasks race to insert cic's
for the same association.  This patch restructures
cfq_get_io_context() such that slow path insertion race is handled
properly.

Note that the restructuring also makes cfq_get_io_context() called
under queue_lock and performs both ioc and cfqd insertions while
holding both ioc and queue locks.  This is part of on-going locking
tightening and will be used to simplify synchronization rules.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

ioprio/cgroup change was handled by marking the changed state in ioc
and, on the following access to the ioc, performing RCU-protected
iteration through all cic's grabbing the matching queue_lock.

This patch moves the changed state to each cic.  When ioprio or cgroup
changes, the respective bit is set on all cic's of the ioc and when
each of those cic (not ioc) is accessed, change is applied for that
specific ioc-queue pair.

This also fixes the following two race conditions between setting and
clearing of changed states.

* Missing barrier between assign/load of ioprio and ioprio_changed
  allowed applying old ioprio.

* Change requests could happen between application of change and
  clearing of changed variables.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Make the following changes to prepare for ioc/cic management cleanup.

* Add cic->q so that ioc can determine the associated queue without
  querying cfq.  This will eventually replace ->key.

* Factor out cfq_release_cic() from cic_free_func().  This function
  assumes that the caller handled locking.

* Rename __cfq_exit_single_io_context() to cfq_exit_cic() and make it
  take only @cic.

* Restructure cfq_cic_link() for future updates.

This patch doesn't introduce any functional changes.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

* blk_get_queue() is peculiar in that it returns 0 on success and 1 on
  failure instead of 0 / -errno or boolean.  Update it such that it
  returns %true on success and %false on failure.

* Make sure the caller checks for the return value.

* Separate out __blk_get_queue() which doesn't check whether @q is
  dead and put it in blk.h.  This will be used later.

This patch doesn't introduce any functional changes.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Ignoring copy_io() during fork, io_context can be allocated from two
places - current_io_context() and set_task_ioprio().  The former is
always called from local task while the latter can be called from
different task.  The synchornization between them are peculiar and
dubious.

* current_io_context() doesn't grab task_lock() and assumes that if it
  saw %NULL ->io_context, it would stay that way until allocation and
  assignment is complete.  It has smp_wmb() between alloc/init and
  assignment.

* set_task_ioprio() grabs task_lock() for assignment and does
  smp_read_barrier_depends() between "ioc = task->io_context" and "if
  (ioc)".  Unfortunately, this doesn't achieve anything - the latter
  is not a dependent load of the former.  ie, if ioc itself were being
  dereferenced "ioc->xxx", it would mean something (not sure what tho)
  but as the code currently stands, the dependent read barrier is
  noop.

As only one of the the two test-assignment sequences is task_lock()
protected, the task_lock() can't do much about race between the two.
Nothing prevents current_io_context() and set_task_ioprio() allocating
its own ioc for the same task and overwriting the other's.

Also, set_task_ioprio() can race with exiting task and create a new
ioc after exit_io_context() is finished.

ioc get/put doesn't have any reason to be complex.  The only hot path
is accessing the existing ioc of %current, which is simple to achieve
given that ->io_context is never destroyed as long as the task is
alive.  All other paths can happily go through task_lock() like all
other task sub structures without impacting anything.

This patch updates ioc get/put so that it becomes more conventional.

* alloc_io_context() is replaced with get_task_io_context().  This is
  the only interface which can acquire access to ioc of another task.
  On return, the caller has an explicit reference to the object which
  should be put using put_io_context() afterwards.

* The functionality of current_io_context() remains the same but when
  creating a new ioc, it shares the code path with
  get_task_io_context() and always goes through task_lock().

* get_io_context() now means incrementing ref on an ioc which the
  caller already has access to (be that an explicit refcnt or implicit
  %current one).

* PF_EXITING inhibits creation of new io_context and once
  exit_io_context() is finished, it's guaranteed that both ioc
  acquisition functions return %NULL.

* All users are updated.  Most are trivial but
  smp_read_barrier_depends() removal from cfq_get_io_context() needs a
  bit of explanation.  I suppose the original intention was to ensure
  ioc->ioprio is visible when set_task_ioprio() allocates new
  io_context and installs it; however, this wouldn't have worked
  because set_task_ioprio() doesn't have wmb between init and install.
  There are other problems with this which will be fixed in another
  patch.

* While at it, use NUMA_NO_NODE instead of -1 for wildcard node
  specification.

-v2: Vivek spotted contamination from debug patch.  Removed.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

* int return from put_io_context() wasn't used by anybody.  Make it
  return void like other put functions and docbook-fy the function
  comment.

* Reorder dummy declarations for !CONFIG_BLOCK case a bit.

* Make alloc_ioc_context() use __GFP_ZERO allocation, take init out of
  if block and drop 0'ing.

* Docbook-fy current_io_context() comment.

This patch doesn't introduce any functional change.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

cfq allocates per-queue id using ida and uses it to index cic radix
tree from io_context.  Move it to q->id and allocate on queue init and
free on queue release.  This simplifies cfq a bit and will allow for
further improvements of io context life-cycle management.

This patch doesn't introduce any functional difference.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

blk_insert_cloned_request(), blk_execute_rq_nowait() and
blk_flush_plug_list() either didn't check whether the queue was dead
or did it without holding queue_lock.  Update them so that dead state
is checked while holding queue_lock.

AFAICS, this plugs all holes (requeue doesn't matter as the request is
transitioning atomically from in_flight to queued).
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

When trying to drain all requests, blk_drain_queue() checked only
q->rq.count[]; however, this only tracks REQ_ALLOCED requests.  This
patch updates blk_drain_queue() such that it looks at all the counters
and queues so that request_queue is actually empty on completion.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

There are a number of QUEUE_FLAG_DEAD tests.  Add blk_queue_dead()
macro and use it.

This patch doesn't introduce any functional difference.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

The only user left for blk_insert_request() is sx8 and it can be
trivially switched to use blk_execute_rq_nowait() - special requests
aren't included in io stat and sx8 doesn't use block layer tagging.
Switch sx8 and kill blk_insert_requeset().

This patch doesn't introduce any functional difference.

Only compile tested.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NJeff Garzik <jgarzik@pobox.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

After flush plug list, the list has no request, so we need to add a
trace_block_plug().
Signed-off-by: NShaohua Li <shaohua.li@intel.com>
Reviewed-by: NNamhyung Kim <namhyung@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

get_request_wait() could sleep and flush the plug list.  If the list is
already flushed, don't flush again.
Signed-off-by: NShaohua Li <shaohua.li@intel.com>
Reviewed-by: NNamhyung Kim <namhyung@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Even after commit 54787556
("block: check for proper length of iov entries earlier ...")
we still won't check for zero-length entries after an unaligned
entry.  Remove the break-statement, so all entries are checked.
Signed-off-by: NBen Hutchings <ben@decadent.org.uk>
Cc: stable@vger.kernel.org
Signed-off-by: NJens Axboe <axboe@kernel.dk>

This reverts commit a72c5e5e.

The commit introduced alias for block devices which is intended to be
used during logging although actual usage hasn't been committed yet.
This approach adds very limited benefit (raw log might be easier to
follow) which can be trivially implemented in userland but has a lot
of problems.

It is much worse than netif renames because it doesn't rename the
actual device but just adds conveninence name which isn't used
universally or enforced.  Everything internal including device lookup
and sysfs still uses the internal name and nothing prevents two
devices from using conflicting alias - ie. sda can have sdb as its
alias.

This has been nacked by people working on device driver core, block
layer and kernel-userland interface and shouldn't have been
upstreamed.  Revert it.

 http://thread.gmane.org/gmane.linux.kernel/1155104
 http://thread.gmane.org/gmane.linux.scsi/68632
 http://thread.gmane.org/gmane.linux.scsi/69776Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NGreg Kroah-Hartman <gregkh@suse.de>
Acked-by: NKay Sievers <kay.sievers@vrfy.org>
Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Cc: Nao Nishijima <nao.nishijima.xt@hitachi.com>
Cc: Alan Cox <alan@linux.intel.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

blk_cleanup_queue() may be called before elevator is set up on a
queue which triggers the following oops.

 BUG: unable to handle kernel NULL pointer dereference at           (null)
 IP: [<ffffffff8125a69c>] elv_drain_elevator+0x1c/0x70
 ...
 Pid: 830, comm: kworker/0:2 Not tainted 3.1.0-next-20111025_64+ #1590
 Bochs Bochs
 RIP: 0010:[<ffffffff8125a69c>]  [<ffffffff8125a69c>] elv_drain_elevator+0x1c/0x70
 ...
 Call Trace:
  [<ffffffff8125da92>] blk_drain_queue+0x42/0x70
  [<ffffffff8125db90>] blk_cleanup_queue+0xd0/0x1c0
  [<ffffffff81469640>] md_free+0x50/0x70
  [<ffffffff8126f43b>] kobject_release+0x8b/0x1d0
  [<ffffffff81270d56>] kref_put+0x36/0xa0
  [<ffffffff8126f2b7>] kobject_put+0x27/0x60
  [<ffffffff814693af>] mddev_delayed_delete+0x2f/0x40
  [<ffffffff81083450>] process_one_work+0x100/0x3b0
  [<ffffffff8108527f>] worker_thread+0x15f/0x3a0
  [<ffffffff81089937>] kthread+0x87/0x90
  [<ffffffff81621834>] kernel_thread_helper+0x4/0x10

Fix it by making blk_cleanup_queue() check whether q->elevator is set
up before invoking blk_drain_queue.
Signed-off-by: NTejun Heo <tj@kernel.org>
Reported-and-tested-by: NJiri Slaby <jslaby@suse.cz>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

This file isn't using full modular functionality, and hence
can be "downgraded" to just using the export.h header.
Reported-by: NStephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: NPaul Gortmaker <paul.gortmaker@windriver.com>

These files were getting <linux/module.h> via an implicit include
path, but we want to crush those out of existence since they cost
time during compiles of processing thousands of lines of headers
for no reason.  Give them the lightweight header that just contains
the EXPORT_SYMBOL infrastructure.
Signed-off-by: NPaul Gortmaker <paul.gortmaker@windriver.com>

We can't use the latter if !CONFIG_LOCKDEP.
Reported-by: NSedat Dilek <sedat.dilek@googlemail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

blkcg->policy_list is protected by blkcg->lock. Its not rcu protected
list. So even for readers, they need to take blkcg->lock. There are
few functions which were reading the list without taking lock. Fix it.
Signed-off-by: NVivek Goyal <vgoyal@redhat.com>
Acked-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

If a rule is being deleted, free up associated policy node. Otherwise
that memory is leaked.
Signed-off-by: NVivek Goyal <vgoyal@redhat.com>
Acked-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

In case tag depth is reduced, it is max_depth not real_max_depth.
So we should allow a request with tag >= max_depth, but for a
tag >= real_max_depth, there really should be some problem.
Signed-off-by: NTao Ma <boyu.mt@taobao.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

The following command sequence triggers an oops.

# mount /dev/sdb1 /mnt
# echo 1 > /sys/class/scsi_device/0\:0\:1\:0/device/delete
# umount /mnt

 general protection fault: 0000 [#1] PREEMPT SMP
 CPU 2
 Modules linked in:

 Pid: 791, comm: umount Not tainted 3.1.0-rc3-work+ #8 Bochs Bochs
 RIP: 0010:[<ffffffff810d0879>]  [<ffffffff810d0879>] __lock_acquire+0x389/0x1d60
...
 Call Trace:
  [<ffffffff810d2845>] lock_acquire+0x95/0x140
  [<ffffffff81aed87b>] _raw_spin_lock+0x3b/0x50
  [<ffffffff811573bc>] bdi_lock_two+0x5c/0x70
  [<ffffffff811c2f6c>] bdev_inode_switch_bdi+0x4c/0xf0
  [<ffffffff811c3fcb>] __blkdev_put+0x11b/0x1d0
  [<ffffffff811c4010>] __blkdev_put+0x160/0x1d0
  [<ffffffff811c40df>] blkdev_put+0x5f/0x190
  [<ffffffff8118f18d>] kill_block_super+0x4d/0x80
  [<ffffffff8118f4a5>] deactivate_locked_super+0x45/0x70
  [<ffffffff8119003a>] deactivate_super+0x4a/0x70
  [<ffffffff811ac4ad>] mntput_no_expire+0xed/0x130
  [<ffffffff811acf2e>] sys_umount+0x7e/0x3a0
  [<ffffffff81aeeeab>] system_call_fastpath+0x16/0x1b

This is because bdev holds on to disk but disk doesn't pin the
associated queue.  If a SCSI device is removed while the device is
still open, the sdev puts the base reference to the queue on release.
When the bdev is finally released, the associated queue is already
gone along with the bdi and bdev_inode_switch_bdi() ends up
dereferencing already freed bdi.

Even if it were not for this bug, disk not holding onto the associated
queue is very unusual and error-prone.

Fix it by making add_disk() take an extra reference to its queue and
put it on disk_release() and ensuring that disk and its fops owner are
put in that order after all accesses to the disk and queue are
complete.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: stable@kernel.org
Signed-off-by: NJens Axboe <axboe@kernel.dk>

A dm-multipath user reported[1] a problem when trying to boot
a kernel with commit 4853abaa
(block: fix flush machinery for stacking drivers with differring
flush flags) applied.  It turns out that an empty flush request
can be sent into blk_insert_flush.  When the BUG_ON was fixed
to allow for this, I/O on the underlying device would stall.  The
reason is that blk_insert_cloned_request does not kick the queue.
In the aforementioned commit, I had added a special case to
kick the queue if data was sent down but the queue flags did
not require a flush.  A better solution is to push the queue
kick up into blk_insert_cloned_request.

This patch, along with a follow-on which fixes the BUG_ON, fixes
the issue reported.

[1] http://www.redhat.com/archives/dm-devel/2011-September/msg00154.htmlReported-by: NChristophe Saout <christophe@saout.de>
Signed-off-by: NJeff Moyer <jmoyer@redhat.com>
Acked-by: NTejun Heo <tj@kernel.org>

Stable note: 3.1
Cc: stable@vger.kernel.org
Signed-off-by: NJens Axboe <axboe@kernel.dk>

A user reported a regression due to commit
4853abaa (block: fix flush
machinery for stacking drivers with differring flush flags).
Part of the problem is that blk_insert_flush required a
single bio be attached to the request.  In reality, having
no attached bio is also a valid case, as can be observed with
an empty flush.

[1] http://www.redhat.com/archives/dm-devel/2011-September/msg00154.htmlReported-by: NChristophe Saout <christophe@saout.de>
Signed-off-by: Jeff Moyer <jmoyer@redhat.com
Acked-by: NTejun Heo <tj@kernel.org>

Stable note: 3.1
Cc: stable@vger.kernel.org
Signed-off-by: NJens Axboe <axboe@kernel.dk>

bio originally has the functionality to set the complete cpu, but
it is broken.

Chirstoph said that "This code is unused, and from the all the
discussions lately pretty obviously broken.  The only thing keeping
it serves is creating more confusion and possibly more bugs."

And Jens replied with "We can kill bio_set_completion_cpu(). I'm fine
with leaving cpu control to the request based drivers, they are the
only ones that can toggle the setting anyway".

So this patch tries to remove all the work of controling complete cpu
from a bio.

Cc: Shaohua Li <shaohua.li@intel.com>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: NTao Ma <boyu.mt@taobao.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

byptes -> bytes.
Signed-off-by: NJie Liu <jeff.liu@oracle.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

request_queue is refcounted but actually depdends on lifetime
management from the queue owner - on blk_cleanup_queue(), block layer
expects that there's no request passing through request_queue and no
new one will.

This is fundamentally broken.  The queue owner (e.g. SCSI layer)
doesn't have a way to know whether there are other active users before
calling blk_cleanup_queue() and other users (e.g. bsg) don't have any
guarantee that the queue is and would stay valid while it's holding a
reference.

With delay added in blk_queue_bio() before queue_lock is grabbed, the
following oops can be easily triggered when a device is removed with
in-flight IOs.

 sd 0:0:1:0: [sdb] Stopping disk
 ata1.01: disabled
 general protection fault: 0000 [#1] PREEMPT SMP
 CPU 2
 Modules linked in:

 Pid: 648, comm: test_rawio Not tainted 3.1.0-rc3-work+ #56 Bochs Bochs
 RIP: 0010:[<ffffffff8137d651>]  [<ffffffff8137d651>] elv_rqhash_find+0x61/0x100
 ...
 Process test_rawio (pid: 648, threadinfo ffff880019efa000, task ffff880019ef8a80)
 ...
 Call Trace:
  [<ffffffff8137d774>] elv_merge+0x84/0xe0
  [<ffffffff81385b54>] blk_queue_bio+0xf4/0x400
  [<ffffffff813838ea>] generic_make_request+0xca/0x100
  [<ffffffff81383994>] submit_bio+0x74/0x100
  [<ffffffff811c53ec>] dio_bio_submit+0xbc/0xc0
  [<ffffffff811c610e>] __blockdev_direct_IO+0x92e/0xb40
  [<ffffffff811c39f7>] blkdev_direct_IO+0x57/0x60
  [<ffffffff8113b1c5>] generic_file_aio_read+0x6d5/0x760
  [<ffffffff8118c1ca>] do_sync_read+0xda/0x120
  [<ffffffff8118ce55>] vfs_read+0xc5/0x180
  [<ffffffff8118cfaa>] sys_pread64+0x9a/0xb0
  [<ffffffff81afaf6b>] system_call_fastpath+0x16/0x1b

This happens because blk_queue_cleanup() destroys the queue and
elevator whether IOs are in progress or not and DEAD tests are
sprinkled in the request processing path without proper
synchronization.

Similar problem exists for blk-throtl.  On queue cleanup, blk-throtl
is shutdown whether it has requests in it or not.  Depending on
timing, it either oopses or throttled bios are lost putting tasks
which are waiting for bio completion into eternal D state.

The way it should work is having the usual clear distinction between
shutdown and release.  Shutdown drains all currently pending requests,
marks the queue dead, and performs partial teardown of the now
unnecessary part of the queue.  Even after shutdown is complete,
reference holders are still allowed to issue requests to the queue
although they will be immmediately failed.  The rest of teardown
happens on release.

This patch makes the following changes to make blk_queue_cleanup()
behave as proper shutdown.

* QUEUE_FLAG_DEAD is now set while holding both q->exit_mutex and
  queue_lock.

* Unsynchronized DEAD check in generic_make_request_checks() removed.
  This couldn't make any meaningful difference as the queue could die
  after the check.

* blk_drain_queue() updated such that it can drain all requests and is
  now called during cleanup.

* blk_throtl updated such that it checks DEAD on grabbing queue_lock,
  drains all throttled bios during cleanup and free td when queue is
  released.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

attempt_plug_merge() accesses elevator without holding queue_lock and
may call into ->elevator_bio_merge_fn().  The elvator is guaranteed to
be valid because it's accessed iff the plugged list has requests and
elevator is never exited with live requests, so as long as the
elevator method can deal with unlocked access, this is safe.

Explain the sync rules around attempt_plug_merge() and drop the
unnecessary @tsk parameter.

This patch doesn't introduce any functional change.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Currently get_request[_wait]() allocates request whether queue is dead
or not.  This patch makes get_request[_wait]() return NULL if @q is
dead.  blk_queue_bio() is updated to fail the submitted bio if request
allocation fails.  While at it, add docbook comments for
get_request[_wait]().

Note that the current code has rather unclear (there are spurious DEAD
tests scattered around) assumption that the owner of a queue
guarantees that no request travels block layer if the queue is dead
and this patch in itself doesn't change much; however, this will allow
fixing the broken assumption in the next patch.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>