linux-sg2042/block
Tejun Heo 0a30288da1 blk-mq, percpu_ref: implement a kludge for SCSI blk-mq stall during probe
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: Tejun Heo <tj@kernel.org>
Reported-by: Christoph Hellwig <hch@infradead.org>
Link: http://lkml.kernel.org/g/20140919113815.GA10791@lst.de
Fixes: add703fda9 ("blk-mq: use percpu_ref for mq usage count")
Cc: Kent Overstreet <kmo@daterainc.com>
Cc: Jens Axboe <axboe@kernel.dk>
Tested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
2014-09-24 08:29:36 -06:00
..
partitions partitions: aix.c: off by one bug 2014-08-05 13:13:24 -06:00
Kconfig block: change config option name for cmdline partition parsing 2013-09-30 14:31:02 -07:00
Kconfig.iosched blkcg: make CONFIG_BLK_CGROUP bool 2012-03-06 21:27:21 +01:00
Makefile block: move mm/bounce.c to block/ 2014-05-19 20:01:52 -06:00
bio-integrity.c block: Fix BUG_ON when pi errors occur 2014-08-21 20:37:47 -05:00
bio.c block: use kmalloc alignment for bio slab 2014-08-01 12:30:34 -04:00
blk-cgroup.c Merge branch 'for-3.17' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup 2014-08-04 10:11:28 -07:00
blk-cgroup.h Revert "block: add __init to blkcg_policy_register" 2014-06-22 16:34:11 -06:00
blk-core.c scsi-mq: fix requests that use a separate CDB buffer 2014-08-22 15:04:31 -05:00
blk-exec.c blk-mq: avoid infinite recursion with the FUA flag 2014-09-22 11:55:19 -06:00
blk-flush.c block: remove elv_abort_queue and blk_abort_flushes 2014-06-11 15:31:21 -06:00
blk-integrity.c bio-integrity: Convert to bvec_iter 2013-11-23 22:33:50 -08:00
blk-ioc.c block: Substitute rcu_access_pointer() for rcu_dereference_raw() 2014-02-18 12:21:26 -08:00
blk-iopoll.c Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip into next 2014-06-03 12:57:53 -07:00
blk-lib.c block/blk-lib.c: make __blkdev_issue_zeroout static 2014-05-26 17:39:09 -06:00
blk-map.c block: remove struct request buffer member 2014-04-15 14:03:02 -06:00
blk-merge.c blk-merge: fix blk_recount_segments 2014-09-02 10:25:12 -06:00
blk-mq-cpu.c blk-mq: add file comments and update copyright notices 2014-05-28 10:15:41 -06:00
blk-mq-cpumap.c blk-mq: add file comments and update copyright notices 2014-05-28 10:15:41 -06:00
blk-mq-sysfs.c blk-mq: blk_mq_unregister_hctx() can be static 2014-05-30 10:31:13 -06:00
blk-mq-tag.c blk-mq: bitmap tag: fix races in bt_get() function 2014-06-17 22:13:08 -07:00
blk-mq-tag.h blk-mq: bitmap tag: fix races on shared ::wake_index fields 2014-06-17 22:12:35 -07:00
blk-mq.c blk-mq, percpu_ref: implement a kludge for SCSI blk-mq stall during probe 2014-09-24 08:29:36 -06:00
blk-mq.h blk-mq: decouble blk-mq freezing from generic bypassing 2014-07-01 10:31:13 -06:00
blk-settings.c block: ensure that bio_add_page() always accepts a page for an empty bio 2014-06-10 12:53:56 -06:00
blk-softirq.c block: fix regression with block enabled tagging 2014-04-09 21:54:06 -06:00
blk-sysfs.c Block: fix unbalanced bypass-disable in blk_register_queue 2014-09-09 10:44:24 -06:00
blk-tag.c block: don't assume last put of shared tags is for the host 2014-07-08 12:25:28 +02:00
blk-throttle.c cgroup: remove sane_behavior support on non-default hierarchies 2014-07-09 10:08:08 -04:00
blk-timeout.c block: ensure that the timer is always added 2014-05-30 15:41:39 -06:00
blk.h block: remove elv_abort_queue and blk_abort_flushes 2014-06-11 15:31:21 -06:00
bounce.c mm: convert some level-less printks to pr_* 2014-06-06 16:08:18 -07:00
bsg-lib.c bsg: Remove unused function bsg_goose_queue() 2012-12-06 14:33:02 +01:00
bsg.c block: add blk_rq_set_block_pc() 2014-06-06 07:57:37 -06:00
cfq-iosched.c cfq-iosched: Add comments on update timing of weight 2014-08-28 08:16:29 -06:00
cmdline-parser.c block: remove unrelated header files and export symbol 2014-01-21 20:18:26 -08:00
compat_ioctl.c Merge branch 'for-3.17/core' of git://git.kernel.dk/linux-block 2014-08-14 09:07:02 -06:00
deadline-iosched.c block: Stop abusing csd.list for fifo_time 2014-02-24 14:46:32 -08:00
elevator.c Revert "block: add __init to elv_register" 2014-06-22 16:34:11 -06:00
genhd.c genhd: fix leftover might_sleep() in blk_free_devt() 2014-09-22 14:45:45 -06:00
ioctl.c block: fix BLKSECTGET ioctl when max_sectors is greater than USHRT_MAX 2014-07-01 10:43:07 -06:00
ioprio.c block: move ioprio.c from fs/ to block/ 2014-05-19 11:02:18 -06:00
noop-iosched.c elevator: Fix a race in elevator switching 2013-07-03 13:25:24 +02:00
partition-generic.c block: Fix dev_t minor allocation lifetime 2014-09-03 15:01:02 -06:00
scsi_ioctl.c block: fix error handling in sg_io 2014-08-26 08:20:01 -06:00