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Guoqing Jiang 54541a75bf md: fix raid10 hang issue caused by barrier [ Upstream commit `e820d55cb9` ] When both regular IO and resync IO happen at the same time, and if we also need to split regular. Then we can see tasks hang due to barrier. 1. resync thread [ 1463.757205] INFO: task md1_resync:5215 blocked for more than 480 seconds. [ 1463.757207] Not tainted 4.19.5-1-default #1 [ 1463.757209] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 1463.757212] md1_resync D 0 5215 2 0x80000000 [ 1463.757216] Call Trace: [ 1463.757223] ? __schedule+0x29a/0x880 [ 1463.757231] ? raise_barrier+0x8d/0x140 [raid10] [ 1463.757236] schedule+0x78/0x110 [ 1463.757243] raise_barrier+0x8d/0x140 [raid10] [ 1463.757248] ? wait_woken+0x80/0x80 [ 1463.757257] raid10_sync_request+0x1f6/0x1e30 [raid10] [ 1463.757265] ? _raw_spin_unlock_irq+0x22/0x40 [ 1463.757284] ? is_mddev_idle+0x125/0x137 [md_mod] [ 1463.757302] md_do_sync.cold.78+0x404/0x969 [md_mod] [ 1463.757311] ? wait_woken+0x80/0x80 [ 1463.757336] ? md_rdev_init+0xb0/0xb0 [md_mod] [ 1463.757351] md_thread+0xe9/0x140 [md_mod] [ 1463.757358] ? _raw_spin_unlock_irqrestore+0x2e/0x60 [ 1463.757364] ? __kthread_parkme+0x4c/0x70 [ 1463.757369] kthread+0x112/0x130 [ 1463.757374] ? kthread_create_worker_on_cpu+0x40/0x40 [ 1463.757380] ret_from_fork+0x3a/0x50 2. regular IO [ 1463.760679] INFO: task kworker/0:8:5367 blocked for more than 480 seconds. [ 1463.760683] Not tainted 4.19.5-1-default #1 [ 1463.760684] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 1463.760687] kworker/0:8 D 0 5367 2 0x80000000 [ 1463.760718] Workqueue: md submit_flushes [md_mod] [ 1463.760721] Call Trace: [ 1463.760731] ? __schedule+0x29a/0x880 [ 1463.760741] ? wait_barrier+0xdd/0x170 [raid10] [ 1463.760746] schedule+0x78/0x110 [ 1463.760753] wait_barrier+0xdd/0x170 [raid10] [ 1463.760761] ? wait_woken+0x80/0x80 [ 1463.760768] raid10_write_request+0xf2/0x900 [raid10] [ 1463.760774] ? wait_woken+0x80/0x80 [ 1463.760778] ? mempool_alloc+0x55/0x160 [ 1463.760795] ? md_write_start+0xa9/0x270 [md_mod] [ 1463.760801] ? try_to_wake_up+0x44/0x470 [ 1463.760810] raid10_make_request+0xc1/0x120 [raid10] [ 1463.760816] ? wait_woken+0x80/0x80 [ 1463.760831] md_handle_request+0x121/0x190 [md_mod] [ 1463.760851] md_make_request+0x78/0x190 [md_mod] [ 1463.760860] generic_make_request+0x1c6/0x470 [ 1463.760870] raid10_write_request+0x77a/0x900 [raid10] [ 1463.760875] ? wait_woken+0x80/0x80 [ 1463.760879] ? mempool_alloc+0x55/0x160 [ 1463.760895] ? md_write_start+0xa9/0x270 [md_mod] [ 1463.760904] raid10_make_request+0xc1/0x120 [raid10] [ 1463.760910] ? wait_woken+0x80/0x80 [ 1463.760926] md_handle_request+0x121/0x190 [md_mod] [ 1463.760931] ? _raw_spin_unlock_irq+0x22/0x40 [ 1463.760936] ? finish_task_switch+0x74/0x260 [ 1463.760954] submit_flushes+0x21/0x40 [md_mod] So resync io is waiting for regular write io to complete to decrease nr_pending (conf->barrier++ is called before waiting). The regular write io splits another bio after call wait_barrier which call nr_pending++, then the splitted bio would continue with raid10_write_request -> wait_barrier, so the splitted bio has to wait for barrier to be zero, then deadlock happens as follows. resync io regular io raise_barrier wait_barrier generic_make_request wait_barrier To resolve the issue, we need to call allow_barrier to decrease nr_pending before generic_make_request since regular IO is not issued to underlying devices, and wait_barrier is called again to ensure no internal IO happening. Fixes: `fc9977dd06` ("md/raid10: simplify the splitting of requests.") Reported-and-tested-by: Siniša Bandin <sinisa@4net.rs> Signed-off-by: Guoqing Jiang <gqjiang@suse.com> Signed-off-by: Shaohua Li <shli@fb.com> Signed-off-by: Sasha Levin <sashal@kernel.org>		2019-02-12 19:47:15 +01:00
arch	powerpc/powernv/ioda: Allocate indirect TCE levels of cached userspace addresses on demand	2019-02-12 19:47:14 +01:00
block	block: use rcu_work instead of call_rcu to avoid sleep in softirq	2019-01-22 21:40:35 +01:00
certs	export.h: remove VMLINUX_SYMBOL() and VMLINUX_SYMBOL_STR()	2018-08-22 23:21:44 +09:00
crypto	crypto: aes_ti - disable interrupts while accessing S-box	2019-02-12 19:46:58 +01:00
Documentation	mm, proc: be more verbose about unstable VMA flags in /proc/<pid>/smaps	2019-01-26 09:32:44 +01:00
drivers	md: fix raid10 hang issue caused by barrier	2019-02-12 19:47:15 +01:00
firmware	kbuild: remove all dummy assignments to obj-	2017-11-18 11:46:06 +09:00
fs	btrfs: use tagged writepage to mitigate livelock of snapshot	2019-02-12 19:47:11 +01:00
include	drbd: Avoid Clang warning about pointless switch statment	2019-02-12 19:47:14 +01:00
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	kobject: return error code if writing /sys/.../uevent fails	2019-02-12 19:47:06 +01:00
lib	fix int_sqrt64() for very large numbers	2019-01-22 21:40:34 +01:00
LICENSES	LICENSES: Remove CC-BY-SA-4.0 license text	2018-10-18 11:28:50 +02:00
mm	percpu: convert spin_lock_irq to spin_lock_irqsave.	2019-02-12 19:47:12 +01:00
net	xfrm6_tunnel: Fix spi check in __xfrm6_tunnel_alloc_spi	2019-02-12 19:47:13 +01:00
samples	livepatch: check kzalloc return values	2019-02-12 19:47:12 +01:00
scripts	modpost: validate symbol names also in find_elf_symbol	2019-02-12 19:47:01 +01:00
security	smack: fix access permissions for keyring	2019-02-12 19:47:05 +01:00
sound	ASoC: fsl: Fix SND_SOC_EUKREA_TLV320 build error on i.MX8M	2019-02-12 19:47:09 +01:00
tools	perf tools: Cast off_t to s64 to avoid warning on bionic libc	2019-02-12 19:47:12 +01:00
usr	initramfs: move gen_initramfs_list.sh from scripts/ to usr/	2018-08-22 23:21:44 +09:00
virt	arm64: KVM: Skip MMIO insn after emulation	2019-02-12 19:47:12 +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 4.19.20	2019-02-06 17:30:16 +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.