Commit Graph

52 Commits

Author SHA1 Message Date
Christoph Hellwig 39795d6534 block: don't hold the queue_lock over blk_abort_request
There is nothing it could synchronize against, so don't go through
the pains of acquiring the lock.

Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-11-15 12:13:18 -07:00
Christoph Hellwig 079076b341 block: remove deadline __deadline manipulation helpers
No users left since the removal of the legacy request interface, we can
remove all the magic bit stealing now and make it a normal field.

But use WRITE_ONCE/READ_ONCE on the new deadline field, given that we
don't seem to have any mechanism to guarantee a new value actually
gets seen by other threads.

Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-11-15 12:13:16 -07:00
Christoph Hellwig 9d037ad707 block: remove req->timeout_list
Unused now that the legacy request path is gone.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-11-09 11:44:10 -07:00
Jens Axboe 4316b79e43 block: kill legacy parts of timeout handling
The only user of legacy timing now is BSG, which is invoked
from the mq timeout handler. Kill the legacy code, and rename
the q->rq_timed_out_fn to q->bsg_job_timeout_fn.

Reviewed-by: Hannes Reinecke <hare@suse.com>
Tested-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-11-07 13:42:33 -07:00
Bart Van Assche f5e350f021 blk-mq: Fix timeout handling in case the timeout handler returns BLK_EH_DONE
Make sure that RQF_TIMED_OUT is cleared when a request is reused
after a block driver timeout handler has returned BLK_EH_DONE.

Fixes: da66126739 ("blk-mq: don't time out requests again that are in the timeout handler")
Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Jianchao Wang <jianchao.w.wang@oracle.com>
Cc: Andrew Randrianasulu <randrianasulu@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-06-23 10:25:45 -06:00
Christoph Hellwig f6e7d48a78 block: remove BLK_EH_HANDLED
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-05-29 08:59:21 -06:00
Christoph Hellwig 6600593cbd block: rename BLK_EH_NOT_HANDLED to BLK_EH_DONE
The BLK_EH_NOT_HANDLED implies nothing happen, but very often that
is not what is happening - instead the driver already completed the
command.  Fix the symbolic name to reflect that a little better.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-05-29 08:59:21 -06:00
Keith Busch 12f5b93145 blk-mq: Remove generation seqeunce
This patch simplifies the timeout handling by relying on the request
reference counting to ensure the iterator is operating on an inflight
and truly timed out request. Since the reference counting prevents the
tag from being reallocated, the block layer no longer needs to prevent
drivers from completing their requests while the timeout handler is
operating on it: a driver completing a request is allowed to proceed to
the next state without additional syncronization with the block layer.

This also removes any need for generation sequence numbers since the
request lifetime is prevented from being reallocated as a new sequence
while timeout handling is operating on it.

To enables this a refcount is added to struct request so that request
users can be sure they're operating on the same request without it
changing while they're processing it.  The request's tag won't be
released for reuse until both the timeout handler and the completion
are done with it.

Signed-off-by: Keith Busch <keith.busch@intel.com>
[hch: slight cleanups, added back submission side hctx lock, use cmpxchg
 for completions]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-05-29 08:59:21 -06:00
Tejun Heo bc6d65e6dc blk-mq: Directly schedule q->timeout_work when aborting a request
Request abortion is performed by overriding deadline to now and
scheduling timeout handling immediately.  For the latter part, the
code was using mod_timer(timeout, 0) which can't guarantee that the
timer runs afterwards.  Let's schedule the underlying work item
directly instead.

This fixes the hangs during probing reported by Sitsofe but it isn't
yet clear to me how the failure can happen reliably if it's just the
above described race condition.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Sitsofe Wheeler <sitsofe@gmail.com>
Reported-by: Meelis Roos <mroos@linux.ee>
Fixes: 358f70da49 ("blk-mq: make blk_abort_request() trigger timeout path")
Cc: stable@vger.kernel.org # v4.16
Link: http://lkml.kernel.org/r/CALjAwxh-PVYFnYFCJpGOja+m5SzZ8Sa4J7ohxdK=r8NyOF-EMA@mail.gmail.com
Link: http://lkml.kernel.org/r/alpine.LRH.2.21.1802261049140.4893@math.ut.ee
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-04-02 16:36:13 -06:00
Bart Van Assche 8814ce8a0f block: Introduce blk_queue_flag_{set,clear,test_and_{set,clear}}()
Introduce functions that modify the queue flags and that protect
these modifications with the request queue lock. Except for moving
one wake_up_all() call from inside to outside a critical section,
this patch does not change any functionality.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-03-08 14:13:48 -07:00
Jens Axboe 0a72e7f449 block: add accessors for setting/querying request deadline
We reduce the resolution of request expiry, but since we're already
using jiffies for this where resolution depends on the kernel
configuration and since the timeout resolution is coarse anyway,
that should be fine.

Reviewed-by: Bart Van Assche <bart.vanassche@wdc.com>
Reviewed-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-01-10 11:47:47 -07:00
Tejun Heo 634f9e4631 blk-mq: remove REQ_ATOM_COMPLETE usages from blk-mq
After the recent updates to use generation number and state based
synchronization, blk-mq no longer depends on REQ_ATOM_COMPLETE except
to avoid firing the same timeout multiple times.

Remove all REQ_ATOM_COMPLETE usages and use a new rq_flags flag
RQF_MQ_TIMEOUT_EXPIRED to avoid firing the same timeout multiple
times.  This removes atomic bitops from hot paths too.

v2: Removed blk_clear_rq_complete() from blk_mq_rq_timed_out().

v3: Added RQF_MQ_TIMEOUT_EXPIRED flag.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: "jianchao.wang" <jianchao.w.wang@oracle.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-01-09 09:31:15 -07:00
Tejun Heo 358f70da49 blk-mq: make blk_abort_request() trigger timeout path
With issue/complete and timeout paths now using the generation number
and state based synchronization, blk_abort_request() is the only one
which depends on REQ_ATOM_COMPLETE for arbitrating completion.

There's no reason for blk_abort_request() to be a completely separate
path.  This patch makes blk_abort_request() piggyback on the timeout
path instead of trying to terminate the request directly.

This removes the last dependency on REQ_ATOM_COMPLETE in blk-mq.

Note that this makes blk_abort_request() asynchronous - it initiates
abortion but the actual termination will happen after a short while,
even when the caller owns the request.  AFAICS, SCSI and ATA should be
fine with that and I think mtip32xx and dasd should be safe but not
completely sure.  It'd be great if people who know the drivers take a
look.

v2: - Add comment explaining the lack of synchronization around
      ->deadline update as requested by Bart.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Asai Thambi SP <asamymuthupa@micron.com>
Cc: Stefan Haberland <sth@linux.vnet.ibm.com>
Cc: Jan Hoeppner <hoeppner@linux.vnet.ibm.com>
Cc: Bart Van Assche <Bart.VanAssche@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-01-09 09:31:15 -07:00
Tejun Heo 1d9bd5161b blk-mq: replace timeout synchronization with a RCU and generation based scheme
Currently, blk-mq timeout path synchronizes against the usual
issue/completion path using a complex scheme involving atomic
bitflags, REQ_ATOM_*, memory barriers and subtle memory coherence
rules.  Unfortunately, it contains quite a few holes.

There's a complex dancing around REQ_ATOM_STARTED and
REQ_ATOM_COMPLETE between issue/completion and timeout paths; however,
they don't have a synchronization point across request recycle
instances and it isn't clear what the barriers add.
blk_mq_check_expired() can easily read STARTED from N-2'th iteration,
deadline from N-1'th, blk_mark_rq_complete() against Nth instance.

In fact, it's pretty easy to make blk_mq_check_expired() terminate a
later instance of a request.  If we induce 5 sec delay before
time_after_eq() test in blk_mq_check_expired(), shorten the timeout to
2s, and issue back-to-back large IOs, blk-mq starts timing out
requests spuriously pretty quickly.  Nothing actually timed out.  It
just made the call on a recycle instance of a request and then
terminated a later instance long after the original instance finished.
The scenario isn't theoretical either.

This patch replaces the broken synchronization mechanism with a RCU
and generation number based one.

1. Each request has a u64 generation + state value, which can be
   updated only by the request owner.  Whenever a request becomes
   in-flight, the generation number gets bumped up too.  This provides
   the basis for the timeout path to distinguish different recycle
   instances of the request.

   Also, marking a request in-flight and setting its deadline are
   protected with a seqcount so that the timeout path can fetch both
   values coherently.

2. The timeout path fetches the generation, state and deadline.  If
   the verdict is timeout, it records the generation into a dedicated
   request abortion field and does RCU wait.

3. The completion path is also protected by RCU (from the previous
   patch) and checks whether the current generation number and state
   match the abortion field.  If so, it skips completion.

4. The timeout path, after RCU wait, scans requests again and
   terminates the ones whose generation and state still match the ones
   requested for abortion.

   By now, the timeout path knows that either the generation number
   and state changed if it lost the race or the completion will yield
   to it and can safely timeout the request.

While it's more lines of code, it's conceptually simpler, doesn't
depend on direct use of subtle memory ordering or coherence, and
hopefully doesn't terminate the wrong instance.

While this change makes REQ_ATOM_COMPLETE synchronization unnecessary
between issue/complete and timeout paths, REQ_ATOM_COMPLETE isn't
removed yet as it's still used in other places.  Future patches will
move all state tracking to the new mechanism and remove all bitops in
the hot paths.

Note that this patch adds a comment explaining a race condition in
BLK_EH_RESET_TIMER path.  The race has always been there and this
patch doesn't change it.  It's just documenting the existing race.

v2: - Fixed BLK_EH_RESET_TIMER handling as pointed out by Jianchao.
    - s/request->gstate_seqc/request->gstate_seq/ as suggested by Peter.
    - READ_ONCE() added in blk_mq_rq_update_state() as suggested by Peter.

v3: - Fixed possible extended seqcount / u64_stats_sync read looping
      spotted by Peter.
    - MQ_RQ_IDLE was incorrectly being set in complete_request instead
      of free_request.  Fixed.

v4: - Rebased on top of hctx_lock() refactoring patch.
    - Added comment explaining the use of hctx_lock() in completion path.

v5: - Added comments requested by Bart.
    - Note the addition of BLK_EH_RESET_TIMER race condition in the
      commit message.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: "jianchao.wang" <jianchao.w.wang@oracle.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Bart Van Assche <Bart.VanAssche@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-01-09 09:31:15 -07:00
Bart Van Assche 4e9b6f2082 block: Fix a race between blk_cleanup_queue() and timeout handling
Make sure that if the timeout timer fires after a queue has been
marked "dying" that the affected requests are finished.

Reported-by: chenxiang (M) <chenxiang66@hisilicon.com>
Fixes: commit 287922eb0b ("block: defer timeouts to a workqueue")
Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Tested-by: chenxiang (M) <chenxiang66@hisilicon.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Keith Busch <keith.busch@intel.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-10-30 13:28:10 -06:00
Peter Zijlstra a7af0af321 blk-mq: attempt to fix atomic flag memory ordering
Attempt to untangle the ordering in blk-mq. The patch introducing the
single smp_mb__before_atomic() is obviously broken in that it doesn't
clearly specify a pairing barrier and an obtained guarantee.

The comment is further misleading in that it hints that the
deadline store and the COMPLETE store also need to be ordered, but
AFAICT there is no such dependency. However what does appear to be
important is the clear happening _after_ the store, and that worked by
pure accident.

This clarifies blk_mq_start_request() -- we should not get there with
STARTING set -- this simplifies the code and makes the barrier usage
sane (the old code could be read to allow not having _any_ atomic after
the barrier, in which case the barrier hasn't got anything to order). We
then also introduce the missing pairing barrier for it.

Also down-grade the barrier to smp_wmb(), this is cheaper for
PowerPC/ARM and doesn't cost anything extra on x86.

And it documents the STARTING vs COMPLETE ordering. Although I've not
been entirely successful in reverse engineering the blk-mq state
machine so there might still be more funnies around timeout vs
requeue.

If I got anything wrong, feel free to educate me by adding comments to
clarify things ;-)

Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Ming Lei <tom.leiming@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Andrea Parri <parri.andrea@gmail.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Bart Van Assche <bart.vanassche@wdc.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Fixes: 538b753418 ("blk-mq: request deadline must be visible before marking rq as started")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-10-04 11:20:11 -06:00
Bart Van Assche 2fff8a924d block: Check locking assumptions at runtime
Instead of documenting the locking assumptions of most block layer
functions as a comment, use lockdep_assert_held() to verify locking
assumptions at runtime.

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Omar Sandoval <osandov@fb.com>
Cc: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-06-20 19:27:14 -06:00
Christoph Hellwig caf7df1227 block: remove the errors field from struct request
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <Bart.VanAssche@sandisk.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
2017-04-20 12:16:10 -06:00
Christoph Hellwig bbc758ec04 block: remove REQ_NO_TIMEOUT flag
This was added for the 'magic' AEN requests in the NVMe driver that never
return.  We now handle them purely inside the driver and don't need this
core hack any more.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
2015-12-22 09:38:34 -07:00
Christoph Hellwig 287922eb0b block: defer timeouts to a workqueue
Timer context is not very useful for drivers to perform any meaningful abort
action from.  So instead of calling the driver from this useless context
defer it to a workqueue as soon as possible.

Note that while a delayed_work item would seem the right thing here I didn't
dare to use it due to the magic in blk_add_timer that pokes deep into timer
internals.  But maybe this encourages Tejun to add a sensible API for that to
the workqueue API and we'll all be fine in the end :)

Contains a major update from Keith Bush:

"This patch removes synchronizing the timeout work so that the timer can
 start a freeze on its own queue. The timer enters the queue, so timer
 context can only start a freeze, but not wait for frozen."

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
2015-12-22 09:38:16 -07:00
Jens Axboe 3b627a3f93 block: clarify blk_add_timer() use case for blk-mq
Just a comment update on not needing queue_lock, and that we aren't
really adding the request to a timeout list for !mq.

Signed-off-by: Jens Axboe <axboe@fb.com>
2015-11-24 15:58:53 -07:00
Christoph Hellwig 55ce0da1da block: fix blk_abort_request for blk-mq drivers
We only added the request to the request list for the !blk-mq case,
so we should only delete it in that case as well.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
2015-11-24 15:24:10 -07:00
Keith Busch 5b3f25fc34 blk-mq: Allow requests to never expire
Some types of requests may be started that are not gauranteed to ever
complete. This adds a request flag that a driver can use so mark the
request as such.

Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
2015-01-08 08:59:01 -07:00
Christoph Hellwig 9041583765 block: fix blk_abort_request on blk-mq
Signed-off-by: Christoph Hellwig <hch@lst.de>

Moved blk_mq_rq_timed_out() definition to the private blk-mq.h header.

Signed-off-by: Jens Axboe <axboe@fb.com>
2014-09-22 12:00:08 -06:00
Ming Lei 5e940aaa59 blk-timeout: fix blk_add_timer
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: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
2014-09-22 12:00:08 -06:00
Christoph Hellwig 46f92d42ee blk-mq: unshared timeout handler
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: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
2014-09-22 12:00:07 -06:00
Jens Axboe c7bca4183f block: ensure that the timer is always added
Commit f793aa5378 relaxed the timer addition a little too much.
If the timer isn't pending, we always need to add it.

Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-30 15:41:39 -06:00
Jens Axboe 0d2602ca30 blk-mq: improve support for shared tags maps
This adds support for active queue tracking, meaning that the
blk-mq tagging maintains a count of active users of a tag set.
This allows us to maintain a notion of fairness between users,
so that we can distribute the tag depth evenly without starving
some users while allowing others to try unfair deep queues.

If sharing of a tag set is detected, each hardware queue will
track the depth of its own queue. And if this exceeds the total
depth divided by the number of active queues, the user is actively
throttled down.

The active queue count is done lazily to avoid bouncing that data
between submitter and completer. Each hardware queue gets marked
active when it allocates its first tag, and gets marked inactive
when 1) the last tag is cleared, and 2) the queue timeout grace
period has passed.

Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-13 15:10:52 -06:00
Christoph Hellwig c4a634f432 block: fold __blk_add_timer into blk_add_timer
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
2014-04-25 08:24:40 -06:00
Jens Axboe 87ee7b1121 blk-mq: fix race with timeouts and requeue events
If a requeue event races with a timeout, we can get into the
situation where we attempt to complete a request from the
timeout handler when it's not start anymore. This causes a crash.
So have the timeout handler check that REQ_ATOM_STARTED is still
set on the request - if not, we ignore the event. If this happens,
the request has now been marked as complete. As a consequence, we
need to ensure to clear REQ_ATOM_COMPLETE in blk_mq_start_request(),
as to maintain proper request state.

Signed-off-by: Jens Axboe <axboe@fb.com>
2014-04-24 08:51:47 -06:00
Jens Axboe f793aa5378 block: relax when to modify the timeout timer
Since we are now, by default, applying timer slack to expiry times,
the logic for when to modify a timer in the block code is suboptimal.
The block layer keeps a forward rolling timer per queue for all
requests, and modifies this timer if a request has a shorter timeout
than what the current expiry time is. However, this breaks down
when our rounded timer values get applied slack. Then each new
request ends up modifying the timer, since we're still a little
in front of the timer + slack.

Fix this by allowing a tolerance of HZ / 2, the timeout handling
doesn't need to be very precise. This drastically cuts down
the number of timer modifications we have to make.

Signed-off-by: Jens Axboe <axboe@fb.com>
2014-04-16 14:15:25 -06:00
Christoph Hellwig 30a91cb4ef blk-mq: rework I/O completions
Rework I/O completions to work more like the old code path.  blk_mq_end_io
now stays out of the business of deferring completions to others CPUs
and calling blk_mark_rq_complete.  The latter is very important to allow
completing requests that have timed out and thus are already marked completed,
the former allows using the IPI callout even for driver specific completions
instead of having to reimplement them.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
2014-02-10 09:27:31 -07:00
Jens Axboe e37459b8e2 Merge branch 'blk-mq/core' into for-3.13/core
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Conflicts:
	block/blk-timeout.c
2013-11-08 09:08:12 -07:00
Duan Jiong 8616ebb16b block: replace IS_ERR and PTR_ERR with PTR_ERR_OR_ZERO
This patch fixes coccinelle error regarding usage of IS_ERR and
PTR_ERR instead of PTR_ERR_OR_ZERO.

Signed-off-by: Duan Jiong <duanj.fnst@cn.fujitsu.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2013-11-08 09:05:30 -07:00
Jeff Moyer 4912aa6c11 block: fix race between request completion and timeout handling
crocode i2c_i801 i2c_core iTCO_wdt iTCO_vendor_support shpchp ioatdma dca be2net sg ses enclosure ext4 mbcache jbd2 sd_mod crc_t10dif ahci megaraid_sas(U) dm_mirror dm_region_hash dm_log dm_mod [last unloaded: scsi_wait_scan]

Pid: 491, comm: scsi_eh_0 Tainted: G        W  ----------------   2.6.32-220.13.1.el6.x86_64 #1 IBM  -[8722PAX]-/00D1461
RIP: 0010:[<ffffffff8124e424>]  [<ffffffff8124e424>] blk_requeue_request+0x94/0xa0
RSP: 0018:ffff881057eefd60  EFLAGS: 00010012
RAX: ffff881d99e3e8a8 RBX: ffff881d99e3e780 RCX: ffff881d99e3e8a8
RDX: ffff881d99e3e8a8 RSI: ffff881d99e3e780 RDI: ffff881d99e3e780
RBP: ffff881057eefd80 R08: ffff881057eefe90 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff881057f92338
R13: 0000000000000000 R14: ffff881057f92338 R15: ffff883058188000
FS:  0000000000000000(0000) GS:ffff880040200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0018 ES: 0018 CR0: 000000008005003b
CR2: 00000000006d3ec0 CR3: 000000302cd7d000 CR4: 00000000000406b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process scsi_eh_0 (pid: 491, threadinfo ffff881057eee000, task ffff881057e29540)
Stack:
 0000000000001057 0000000000000286 ffff8810275efdc0 ffff881057f16000
<0> ffff881057eefdd0 ffffffff81362323 ffff881057eefe20 ffffffff8135f393
<0> ffff881057e29af8 ffff8810275efdc0 ffff881057eefe78 ffff881057eefe90
Call Trace:
 [<ffffffff81362323>] __scsi_queue_insert+0xa3/0x150
 [<ffffffff8135f393>] ? scsi_eh_ready_devs+0x5e3/0x850
 [<ffffffff81362a23>] scsi_queue_insert+0x13/0x20
 [<ffffffff8135e4d4>] scsi_eh_flush_done_q+0x104/0x160
 [<ffffffff8135fb6b>] scsi_error_handler+0x35b/0x660
 [<ffffffff8135f810>] ? scsi_error_handler+0x0/0x660
 [<ffffffff810908c6>] kthread+0x96/0xa0
 [<ffffffff8100c14a>] child_rip+0xa/0x20
 [<ffffffff81090830>] ? kthread+0x0/0xa0
 [<ffffffff8100c140>] ? child_rip+0x0/0x20
Code: 00 00 eb d1 4c 8b 2d 3c 8f 97 00 4d 85 ed 74 bf 49 8b 45 00 49 83 c5 08 48 89 de 4c 89 e7 ff d0 49 8b 45 00 48 85 c0 75 eb eb a4 <0f> 0b eb fe 0f 1f 84 00 00 00 00 00 55 48 89 e5 0f 1f 44 00 00
RIP  [<ffffffff8124e424>] blk_requeue_request+0x94/0xa0
 RSP <ffff881057eefd60>

The RIP is this line:
        BUG_ON(blk_queued_rq(rq));

After digging through the code, I think there may be a race between the
request completion and the timer handler running.

A timer is started for each request put on the device's queue (see
blk_start_request->blk_add_timer).  If the request does not complete
before the timer expires, the timer handler (blk_rq_timed_out_timer)
will mark the request complete atomically:

static inline int blk_mark_rq_complete(struct request *rq)
{
        return test_and_set_bit(REQ_ATOM_COMPLETE, &rq->atomic_flags);
}

and then call blk_rq_timed_out.  The latter function will call
scsi_times_out, which will return one of BLK_EH_HANDLED,
BLK_EH_RESET_TIMER or BLK_EH_NOT_HANDLED.  If BLK_EH_RESET_TIMER is
returned, blk_clear_rq_complete is called, and blk_add_timer is again
called to simply wait longer for the request to complete.

Now, if the request happens to complete while this is going on, what
happens?  Given that we know the completion handler will bail if it
finds the REQ_ATOM_COMPLETE bit set, we need to focus on the completion
handler running after that bit is cleared.  So, from the above
paragraph, after the call to blk_clear_rq_complete.  If the completion
sets REQ_ATOM_COMPLETE before the BUG_ON in blk_add_timer, we go boom
there (I haven't seen this in the cores).  Next, if we get the
completion before the call to list_add_tail, then the timer will
eventually fire for an old req, which may either be freed or reallocated
(there is evidence that this might be the case).  Finally, if the
completion comes in *after* the addition to the timeout list, I think
it's harmless.  The request will be removed from the timeout list,
req_atom_complete will be set, and all will be well.

This will only actually explain the coredumps *IF* the request
structure was freed, reallocated *and* queued before the error handler
thread had a chance to process it.  That is possible, but it may make
sense to keep digging for another race.  I think that if this is what
was happening, we would see other instances of this problem showing up
as null pointer or garbage pointer dereferences, for example when the
request structure was not re-used.  It looks like we actually do run
into that situation in other reports.

This patch moves the BUG_ON(test_bit(REQ_ATOM_COMPLETE,
&req->atomic_flags)); from blk_add_timer to the only caller that could
trip over it (blk_start_request).  It then inverts the calls to
blk_clear_rq_complete and blk_add_timer in blk_rq_timed_out to address
the race.  I've boot tested this patch, but nothing more.

Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Acked-by: Hannes Reinecke <hare@suse.de>
Cc: stable@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2013-11-08 08:59:04 -07:00
Jens Axboe 320ae51fee blk-mq: new multi-queue block IO queueing mechanism
Linux currently has two models for block devices:

- The classic request_fn based approach, where drivers use struct
  request units for IO. The block layer provides various helper
  functionalities to let drivers share code, things like tag
  management, timeout handling, queueing, etc.

- The "stacked" approach, where a driver squeezes in between the
  block layer and IO submitter. Since this bypasses the IO stack,
  driver generally have to manage everything themselves.

With drivers being written for new high IOPS devices, the classic
request_fn based driver doesn't work well enough. The design dates
back to when both SMP and high IOPS was rare. It has problems with
scaling to bigger machines, and runs into scaling issues even on
smaller machines when you have IOPS in the hundreds of thousands
per device.

The stacked approach is then most often selected as the model
for the driver. But this means that everybody has to re-invent
everything, and along with that we get all the problems again
that the shared approach solved.

This commit introduces blk-mq, block multi queue support. The
design is centered around per-cpu queues for queueing IO, which
then funnel down into x number of hardware submission queues.
We might have a 1:1 mapping between the two, or it might be
an N:M mapping. That all depends on what the hardware supports.

blk-mq provides various helper functions, which include:

- Scalable support for request tagging. Most devices need to
  be able to uniquely identify a request both in the driver and
  to the hardware. The tagging uses per-cpu caches for freed
  tags, to enable cache hot reuse.

- Timeout handling without tracking request on a per-device
  basis. Basically the driver should be able to get a notification,
  if a request happens to fail.

- Optional support for non 1:1 mappings between issue and
  submission queues. blk-mq can redirect IO completions to the
  desired location.

- Support for per-request payloads. Drivers almost always need
  to associate a request structure with some driver private
  command structure. Drivers can tell blk-mq this at init time,
  and then any request handed to the driver will have the
  required size of memory associated with it.

- Support for merging of IO, and plugging. The stacked model
  gets neither of these. Even for high IOPS devices, merging
  sequential IO reduces per-command overhead and thus
  increases bandwidth.

For now, this is provided as a potential 3rd queueing model, with
the hope being that, as it matures, it can replace both the classic
and stacked model. That would get us back to having just 1 real
model for block devices, leaving the stacked approach to dm/md
devices (as it was originally intended).

Contributions in this patch from the following people:

Shaohua Li <shli@fusionio.com>
Alexander Gordeev <agordeev@redhat.com>
Christoph Hellwig <hch@infradead.org>
Mike Christie <michaelc@cs.wisc.edu>
Matias Bjorling <m@bjorling.me>
Jeff Moyer <jmoyer@redhat.com>

Acked-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2013-10-25 11:56:00 +01:00
Hannes Reinecke 80bd7181b0 block: check for timeout function in blk_rq_timed_out()
rq_timed_out_fn might have been unset while the request
was in flight, so we need to check for it in blk_rq_timed_out().

Acked-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Stefan Weinhuber <wein@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
2013-07-01 17:31:23 +02:00
Asias He 76aaa5101f block: Drop dead function blk_abort_queue()
This function was only used by btrfs code in btrfs_abort_devices()
(seems in a wrong way).

It was removed in commit d07eb91170,
So, Let's remove the dead code to avoid any confusion.

Changes in v2: update commit log, btrfs_abort_devices() was removed
already.

Cc: Jens Axboe <axboe@kernel.dk>
Cc: linux-kernel@vger.kernel.org
Cc: Chris Mason <chris.mason@oracle.com>
Cc: linux-btrfs@vger.kernel.org
Cc: David Sterba <dave@jikos.cz>
Signed-off-by: Asias He <asias@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2012-06-15 08:46:23 +02:00
Akinobu Mita dd48c085c1 fault-injection: add ability to export fault_attr in arbitrary directory
init_fault_attr_dentries() is used to export fault_attr via debugfs.
But it can only export it in debugfs root directory.

Per Forlin is working on mmc_fail_request which adds support to inject
data errors after a completed host transfer in MMC subsystem.

The fault_attr for mmc_fail_request should be defined per mmc host and
export it in debugfs directory per mmc host like
/sys/kernel/debug/mmc0/mmc_fail_request.

init_fault_attr_dentries() doesn't help for mmc_fail_request.  So this
introduces fault_create_debugfs_attr() which is able to create a
directory in the arbitrary directory and replace
init_fault_attr_dentries().

[akpm@linux-foundation.org: extraneous semicolon, per Randy]
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Tested-by: Per Forlin <per.forlin@linaro.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Matt Mackall <mpm@selenic.com>
Cc: Randy Dunlap <rdunlap@xenotime.net>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-08-03 14:25:20 -10:00
Richard Kennedy a534dbe96e block: ensure jiffies wrap is handled correctly in blk_rq_timed_out_timer
blk_rq_timed_out_timer() relied on blk_add_timer() never returning a
timer value of zero, but commit 7838c15b8d
removed the code that bumped this value when it was zero.
Therefore when jiffies is near wrap we could get unlucky & not set the
timeout value correctly.

This patch uses a flag to indicate that the timeout value was set and so
handles jiffies wrap correctly, and it keeps all the logic in one
function so should be easier to maintain in the future.

Signed-off-by: Richard Kennedy <richard@rsk.demon.co.uk>
Cc: stable@kernel.org
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2010-04-21 17:42:08 +02:00
Tejun Heo 2eef33e439 block: clean up misc stuff after block layer timeout conversion
* In blk_rq_timed_out_timer(), else { if } to else if

* In blk_add_timer(), simplify if/else block

[ Impact: cleanup ]

Signed-off-by: Tejun Heo <tj@kernel.org>
2009-04-28 07:37:34 +02:00
Hannes Reinecke 17d5c8ca75 block: fix intermittent dm timeout based oops
Very rarely under stress testing of dm, oopses are occuring as
something tampers with an old stack frame.  This has been traced back
to blk_abort_queue() leaving a timeout_list pointing to the stack.
The reason is that sometimes blk_abort_request() won't delete the
timer (if the request is marked as complete but before the timer has
been removed, a small race window).  Fix this by splicing back from
the ususally empty list to the q->timeout_list.

Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-04-24 08:54:21 +02:00
Jens Axboe b759113499 block: make blk_abort_queue() ignore non-request based devices
There's nothing to do for those devices, since the timeout handling is
based on requests.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-04-22 08:35:10 +02:00
Hannes Reinecke be987fdb55 block: fix deadlock in blk_abort_queue() for drivers that readd to timeout list
blk_abort_queue() iterates the timeout list and aborts each request on the
list, but if the driver error handling readds a request to the timeout list
during this processing, we could be looping forever. Fix this by splicing
current entries to a local list and run over that list instead.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-02-18 10:34:16 +01:00
Jens Axboe 70ed28b92a block: leave the request timeout timer running even on an empty list
For sync IO, we'll often do them serialized. This means we'll be touching
the queue timer for every IO, as opposed to only occasionally like we
do for queued IO. Instead of deleting the timer when the last request
is removed, just let continue running. If a new request comes up soon
we then don't have to readd the timer again. If no new requests arrive,
the timer will expire without side effect later.

This improves high iops sync IO by ~1%.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-12-29 08:28:42 +01:00
Jens Axboe 65d3618ccf block: add comment in blk_rq_timed_out() about why next can not be 0
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-12-29 08:28:42 +01:00
malahal@us.ibm.com 565e411d76 block: optimizations in blk_rq_timed_out_timer()
Now the rq->deadline can't be zero if the request is in the
timeout_list, so there is no need to have next_set. There is no need to
access a request's deadline field if blk_rq_timed_out is called on it.

Signed-off-by: Malahal Naineni <malahal@us.ibm.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-12-29 08:28:42 +01:00
Alan Stern 7838c15b8d Block: use round_jiffies_up()
This patch (as1159b) changes the timeout routines in the block core to
use round_jiffies_up().  There's no point in rounding the timer
deadline down, since if it expires too early we will have to restart
it.

The patch also removes some unnecessary tests when a request is
removed from the queue's timer list.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-11-06 08:42:49 +01:00
Jens Axboe 7ba1fbaa4a block: use rq complete marking in blk_abort_request()
We cannot abort a request if we raced with the timeout handler already,
or with the IO completion. So make blk_abort_request() mark the request
as complete, and only continue if we succeeded.

Found and suggested by Mike Anderson <andmike@linux.vnet.ibm.com>

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09 08:56:17 +02:00
Jens Axboe 581d4e28d9 block: add fault injection mechanism for faking request timeouts
Only works for the generic request timer handling. Allows one to
sporadically ignore request completions, thus exercising the timeout
handling.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09 08:56:17 +02:00