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Liu Bo 6d482bc569 blk-iolatency: fix IO hang due to negative inflight counter 
[ Upstream commit 8c772a9bfc ]

Our test reported the following stack, and vmcore showed that
->inflight counter is -1.

[ffffc9003fcc38d0] __schedule at ffffffff8173d95d
[ffffc9003fcc3958] schedule at ffffffff8173de26
[ffffc9003fcc3970] io_schedule at ffffffff810bb6b6
[ffffc9003fcc3988] blkcg_iolatency_throttle at ffffffff813911cb
[ffffc9003fcc3a20] rq_qos_throttle at ffffffff813847f3
[ffffc9003fcc3a48] blk_mq_make_request at ffffffff8137468a
[ffffc9003fcc3b08] generic_make_request at ffffffff81368b49
[ffffc9003fcc3b68] submit_bio at ffffffff81368d7d
[ffffc9003fcc3bb8] ext4_io_submit at ffffffffa031be00 [ext4]
[ffffc9003fcc3c00] ext4_writepages at ffffffffa03163de [ext4]
[ffffc9003fcc3d68] do_writepages at ffffffff811c49ae
[ffffc9003fcc3d78] __filemap_fdatawrite_range at ffffffff811b6188
[ffffc9003fcc3e30] filemap_write_and_wait_range at ffffffff811b6301
[ffffc9003fcc3e60] ext4_sync_file at ffffffffa030cee8 [ext4]
[ffffc9003fcc3ea8] vfs_fsync_range at ffffffff8128594b
[ffffc9003fcc3ee8] do_fsync at ffffffff81285abd
[ffffc9003fcc3f18] sys_fsync at ffffffff81285d50
[ffffc9003fcc3f28] do_syscall_64 at ffffffff81003c04
[ffffc9003fcc3f50] entry_SYSCALL_64_after_swapgs at ffffffff81742b8e

The ->inflight counter may be negative (-1) if

1) blk-iolatency was disabled when the IO was issued,

2) blk-iolatency was enabled before this IO reached its endio,

3) the ->inflight counter is decreased from 0 to -1 in endio()

In fact the hang can be easily reproduced by the below script,

H=/sys/fs/cgroup/unified/
P=/sys/fs/cgroup/unified/test

echo "+io" > $H/cgroup.subtree_control
mkdir -p $P

echo $$ > $P/cgroup.procs

xfs_io -f -d -c "pwrite 0 4k" /dev/sdg

echo "`cat /sys/block/sdg/dev` target=1000000" > $P/io.latency

xfs_io -f -d -c "pwrite 0 4k" /dev/sdg

This fixes the problem by freezing the queue so that while
enabling/disabling iolatency, there is no inflight rq running.

Note that quiesce_queue is not needed as this only updating iolatency
configuration about which dispatching request_queue doesn't care.

Signed-off-by: Liu Bo <bo.liu@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2019-03-13 14:02:38 -07:00
arch MIPS: Remove function size check in get_frame_info() 2019-03-13 14:02:37 -07:00
block blk-iolatency: fix IO hang due to negative inflight counter 2019-03-13 14:02:38 -07:00
certs export.h: remove VMLINUX_SYMBOL() and VMLINUX_SYMBOL_STR() 2018-08-22 23:21:44 +09:00
crypto net: crypto set sk to NULL when af_alg_release. 2019-02-23 09:07:24 +01:00
Documentation dt-bindings: eeprom: at24: add "atmel,24c2048" compatible string 2019-02-20 10:25:35 +01:00
drivers qede: Fix system crash on configuring channels. 2019-03-13 14:02:38 -07:00
firmware kbuild: remove all dummy assignments to obj- 2017-11-18 11:46:06 +09:00
fs fs: ratelimit __find_get_block_slow() failure message. 2019-03-13 14:02:38 -07:00
include irqchip/gic-v3-its: Fix ITT_entry_size accessor 2019-03-13 14:02:35 -07:00
init kbuild: Disable LD_DEAD_CODE_DATA_ELIMINATION with ftrace & GCC <= 4.7 2019-01-22 21:40:34 +01:00
ipc ipc/shm.c: use ERR_CAST() for shm_lock() error return 2018-10-05 16:32:04 -07:00
kernel bpf: Fix syscall's stackmap lookup potential deadlock 2019-03-13 14:02:36 -07:00
lib lib/test_kmod.c: potential double free in error handling 2019-03-13 14:02:32 -07:00
LICENSES LICENSES: Remove CC-BY-SA-4.0 license text 2018-10-18 11:28:50 +02:00
mm mm, memory_hotplug: fix off-by-one in is_pageblock_removable 2019-03-13 14:02:32 -07:00
net netfilter: nf_nat: skip nat clash resolution for same-origin entries 2019-03-13 14:02:37 -07:00
samples samples: mei: use /dev/mei0 instead of /dev/mei 2019-02-15 08:10:11 +01:00
scripts scripts/gdb: fix lx-version string output 2019-02-12 19:47:20 +01:00
security apparmor: Fix aa_label_build() error handling for failed merges 2019-03-13 14:02:32 -07:00
sound ASoC: imx-audmux: change snprintf to scnprintf for possible overflow 2019-03-05 17:58:47 +01:00
tools perf trace: Support multiple "vfs_getname" probes 2019-03-13 14:02:37 -07:00
usr initramfs: move gen_initramfs_list.sh from scripts/ to usr/ 2018-08-22 23:21:44 +09:00
virt kvm: fix kvm_ioctl_create_device() reference counting (CVE-2019-6974) 2019-02-12 19:47:25 +01:00
.clang-format clang-format: Set IndentWrappedFunctionNames false 2018-08-01 18:38:51 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Kbuild updates for v4.17 (2nd) 2018-04-15 17:21:30 -07:00
.mailmap libnvdimm-for-4.19_misc 2018-08-25 18:13:10 -07:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS 9p: remove Ron Minnich from MAINTAINERS 2018-08-17 16:20:26 -07:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt 2018-08-02 08:06:55 +09:00
MAINTAINERS MAINTAINERS: Add Sasha as a stable branch maintainer 2018-12-01 09:37:25 +01:00
Makefile Linux 4.19.28 2019-03-10 07:17:22 +01:00
README Docs: Added a pointer to the formatted docs to README 2018-03-21 09:02:53 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.