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Brian Foster 50e7d6c7a5 iomap: clean up writeback state logic on writepage error 
The iomap writepage error handling logic is a mash of old and
slightly broken XFS writepage logic. When keepwrite writeback state
tracking was introduced in XFS in commit 0d085a529b ("xfs: ensure
WB_SYNC_ALL writeback handles partial pages correctly"), XFS had an
additional cluster writeback context that scanned ahead of
->writepage() to process dirty pages over the current ->writepage()
extent mapping. This context expected a dirty page and required
retention of the TOWRITE tag on partial page processing so the
higher level writeback context would revisit the page (in contrast
to ->writepage(), which passes a page with the dirty bit already
cleared).

The cluster writeback mechanism was eventually removed and some of
the error handling logic folded into the primary writeback path in
commit 150d5be09c ("xfs: remove xfs_cancel_ioend"). This patch
accidentally conflated the two contexts by using the keepwrite logic
in ->writepage() without accounting for the fact that the page is
not dirty. Further, the keepwrite logic has no practical effect on
the core ->writepage() caller (write_cache_pages()) because it never
revisits a page in the current function invocation.

Technically, the page should be redirtied for the keepwrite logic to
have any effect. Otherwise, write_cache_pages() may find the tagged
page but will skip it since it is clean. Even if the page was
redirtied, however, there is still no practical effect to keepwrite
since write_cache_pages() does not wrap around within a single
invocation of the function. Therefore, the dirty page would simply
end up retagged on the next writeback sequence over the associated
range.

All that being said, none of this really matters because redirtying
a partially processed page introduces a potential infinite redirty
-> writeback failure loop that deviates from the current design
principle of clearing the dirty state on writepage failure to avoid
building up too much dirty, unreclaimable memory on the system.
Therefore, drop the spurious keepwrite usage and dirty state
clearing logic from iomap_writepage_map(), treat the partially
processed page the same as a fully processed page, and let the
imminent ioend failure clean up the writeback state.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
2020-11-04 08:52:46 -08:00
arch treewide: Convert macro and uses of __section(foo) to __section("foo") 2020-10-25 14:51:49 -07:00
block block-5.10-2020-10-24 2020-10-24 12:46:42 -07:00
certs .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
crypto drivers-5.10-2020-10-12 2020-10-13 13:04:41 -07:00
Documentation xen: branch for v5.10-rc1c 2020-10-25 10:55:35 -07:00
drivers treewide: Convert macro and uses of __section(foo) to __section("foo") 2020-10-25 14:51:49 -07:00
fs iomap: clean up writeback state logic on writepage error 2020-11-04 08:52:46 -08:00
include iomap: support partial page discard on writeback block mapping failure 2020-11-04 08:52:46 -08:00
init linux-kselftest-kunit-5.10-rc1 2020-10-18 14:45:59 -07:00
ipc ipc: adjust proc_ipc_sem_dointvec definition to match prototype 2020-09-05 12:14:29 -07:00
kernel treewide: Convert macro and uses of __section(foo) to __section("foo") 2020-10-25 14:51:49 -07:00
lib random32: make prandom_u32() less predictable 2020-10-25 10:40:08 -07:00
LICENSES LICENSES/deprecated: add Zlib license text 2020-09-16 14:33:49 +02:00
mm Refactored code for 5.10: 2020-10-23 11:33:41 -07:00
net mm: remove kzfree() compatibility definition 2020-10-25 11:39:02 -07:00
samples bpf, libbpf: Guard bpf inline asm from bpf_tail_call_static 2020-10-22 01:46:52 +02:00
scripts treewide: Convert macro and uses of __section(foo) to __section("foo") 2020-10-25 14:51:49 -07:00
security SafeSetID changes for v5.10 2020-10-25 10:45:26 -07:00
sound ARM: SoC platform updates 2020-10-24 10:33:08 -07:00
tools treewide: Convert macro and uses of __section(foo) to __section("foo") 2020-10-25 14:51:49 -07:00
usr Merge branch 'work.fdpic' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-08-07 13:29:39 -07:00
virt kvm: x86/mmu: Support dirty logging for the TDP MMU 2020-10-23 03:42:13 -04:00
.clang-format RDMA 5.10 pull request 2020-10-17 11:18:18 -07:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: docs: ignore sphinx_*/ directories 2020-09-10 10:44:31 -06:00
.mailmap MAINTAINERS: jarkko.sakkinen@linux.intel.com -> jarkko@kernel.org 2020-10-16 11:11:19 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS networking changes for the 5.10 merge window 2020-10-15 18:42:13 -07:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS ARM: Devicetree updates 2020-10-24 10:44:18 -07:00
Makefile Linux 5.10-rc1 2020-10-25 15:14:11 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -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.

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.