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Zygo Blaxell d35115930d btrfs: remove spurious WARN_ON(ref->count < 0) in find_parent_nodes
commit c8195a7b1a upstream.

Until v4.14, this warning was very infrequent:

	WARNING: CPU: 3 PID: 18172 at fs/btrfs/backref.c:1391 find_parent_nodes+0xc41/0x14e0
	Modules linked in: [...]
	CPU: 3 PID: 18172 Comm: bees Tainted: G      D W    L  4.11.9-zb64+ #1
	Hardware name: System manufacturer System Product Name/M5A78L-M/USB3, BIOS 2101    12/02/2014
	Call Trace:
	 dump_stack+0x85/0xc2
	 __warn+0xd1/0xf0
	 warn_slowpath_null+0x1d/0x20
	 find_parent_nodes+0xc41/0x14e0
	 __btrfs_find_all_roots+0xad/0x120
	 ? extent_same_check_offsets+0x70/0x70
	 iterate_extent_inodes+0x168/0x300
	 iterate_inodes_from_logical+0x87/0xb0
	 ? iterate_inodes_from_logical+0x87/0xb0
	 ? extent_same_check_offsets+0x70/0x70
	 btrfs_ioctl+0x8ac/0x2820
	 ? lock_acquire+0xc2/0x200
	 do_vfs_ioctl+0x91/0x700
	 ? __fget+0x112/0x200
	 SyS_ioctl+0x79/0x90
	 entry_SYSCALL_64_fastpath+0x23/0xc6
	 ? trace_hardirqs_off_caller+0x1f/0x140

Starting with v4.14 (specifically 86d5f99442 ("btrfs: convert prelimary
reference tracking to use rbtrees")) the WARN_ON occurs three orders of
magnitude more frequently--almost once per second while running workloads
like bees.

Replace the WARN_ON() with a comment rationale for its removal.
The rationale is paraphrased from an explanation by Edmund Nadolski
<enadolski@suse.de> on the linux-btrfs mailing list.

Fixes: 8da6d5815c ("Btrfs: added btrfs_find_all_roots()")
Signed-off-by: Zygo Blaxell <ce3g8jdj@umail.furryterror.org>
Reviewed-by: Lu Fengqi <lufq.fnst@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2018-03-21 12:06:44 +01:00
arch parisc: Handle case where flush_cache_range is called with no context 2018-03-21 12:06:42 +01:00
block blk-mq: don't call io sched's .requeue_request when requeueing rq to ->dispatch 2018-03-08 22:41:20 -08:00
certs License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
crypto crypto: ecc - Fix NULL pointer deref. on no default_rng 2018-03-19 08:42:49 +01:00
Documentation usb: host: xhci-rcar: add support for r8a77965 2018-03-19 08:42:45 +01:00
drivers irqchip/gic-v3-its: Ensure nr_ites >= nr_lpis 2018-03-21 12:06:44 +01:00
firmware License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
fs btrfs: remove spurious WARN_ON(ref->count < 0) in find_parent_nodes 2018-03-21 12:06:44 +01:00
include KVM: arm/arm64: vgic: Don't populate multiple LRs with the same vintid 2018-03-21 12:06:43 +01:00
init kmemcheck: stop using GFP_NOTRACK and SLAB_NOTRACK 2018-02-22 15:42:23 +01:00
ipc License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
kernel locking/locktorture: Fix num reader/writer corner cases 2018-03-19 08:42:56 +01:00
lib Fix misannotated out-of-line _copy_to_user() 2018-03-19 08:42:56 +01:00
mm mm/memblock.c: hardcode the end_pfn being -1 2018-03-15 10:54:32 +01:00
net mac80211: remove BUG() when interface type is invalid 2018-03-19 08:42:55 +01:00
samples samples/bpf: adjust rlimit RLIMIT_MEMLOCK for xdp1 2017-12-20 10:10:31 +01:00
scripts objtool, retpolines: Integrate objtool with retpoline support more closely 2018-03-15 10:54:38 +01:00
security ima: relax requiring a file signature for new files with zero length 2018-03-19 08:42:56 +01:00
sound ALSA: seq: Clear client entry before deleting else at closing 2018-03-21 12:06:42 +01:00
tools selftests/x86/entry_from_vm86: Add test cases for POPF 2018-03-21 12:06:41 +01:00
usr initramfs: fix initramfs rebuilds w/ compression after disabling 2017-11-03 07:39:19 -07:00
virt KVM: arm/arm64: vgic: Don't populate multiple LRs with the same vintid 2018-03-21 12:06:43 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Add hch to .get_maintainer.ignore 2015-08-21 14:30:10 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore kbuild: rpm-pkg: keep spec file until make mrproper 2018-02-13 10:19:46 +01:00
.mailmap .mailmap: Add Maciej W. Rozycki's Imagination e-mail address 2017-11-10 12:16:15 -08:00
COPYING [PATCH] update FSF address in COPYING 2005-09-10 10:06:29 -07:00
CREDITS MAINTAINERS: update TPM driver infrastructure changes 2017-11-09 17:58:40 -08:00
Kbuild License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
Kconfig License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
MAINTAINERS dt-bindings: Document mti,mips-cpc binding 2018-03-15 10:54:35 +01:00
Makefile Linux 4.14.28 2018-03-19 08:42:57 +01:00
README README: add a new README file, pointing to the Documentation/ 2016-10-24 08:12:35 -02:00

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

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

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.