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Eryu Guan c771c14baa iomap: invalidate page caches should be after iomap_dio_complete() in direct write After XFS switching to iomap based DIO (commit `acdda3aae1` ("xfs: use iomap_dio_rw")), I started to notice dio29/dio30 tests failures from LTP run on ppc64 hosts, and they can be reproduced on x86_64 hosts with 512B/1k block size XFS too. dio29 diotest3 -b 65536 -n 100 -i 1000 -o 1024000 dio30 diotest6 -b 65536 -n 100 -i 1000 -o 1024000 The failure message is like: bufcmp: offset 0: Expected: 0x62, got 0x0 diotest03 1 TPASS : Read with Direct IO, Write without diotest03 2 TFAIL : diotest3.c:142: comparsion failed; child=98 offset=1425408 diotest03 3 TFAIL : diotest3.c:194: Write Direct-child 98 failed Direct write wrote 0x62 but buffer read got zero. This is because, when doing direct write to a hole or preallocated file, we invalidate the page caches before converting the extent from unwritten state to normal state, which is done by iomap_dio_complete(), thus leave a window for other buffer reader to cache the unwritten state extent. Consider this case, with sub-page blocksize XFS, two processes are direct writing to different blocksize-aligned regions (say 512B) of the same preallocated file, and reading the region back via buffered I/O to compare contents. process A, region [0,512] process B, region [512,1024] xfs_file_write_iter xfs_file_aio_dio_write iomap_dio_rw iomap_apply invalidate_inode_pages2_range xfs_file_write_iter xfs_file_aio_dio_write iomap_dio_rw iomap_apply invalidate_inode_pages2_range iomap_dio_complete xfs_file_read_iter xfs_file_buffered_aio_read generic_file_read_iter do_generic_file_read <readahead fills pagecache with 0> iomap_dio_complete xfs_file_read_iter <read gets 0 from pagecache> Process A first invalidates page caches, at this point the underlying extent is still in unwritten state (iomap_dio_complete not called yet), and process B finishs direct write and populates page caches via readahead, which caches zeros in page for region A, then process A reads zeros from page cache, instead of the actual data. Fix it by invalidating page caches after converting unwritten extent to make sure we read content from disk after extent state changed, as what we did before switching to iomap based dio. Also introduce a new 'start' variable to save the original write offset (iomap_dio_complete() updates iocb->ki_pos), and a 'err' variable for invalidating caches result, cause we can't reuse 'ret' anymore. Signed-off-by: Eryu Guan <eguan@redhat.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>		2017-03-06 09:50:01 -08:00
arch	Second batch of KVM changes for 4.11 merge window	2017-03-04 11:36:19 -08:00
block	Merge branch 'for-linus' of git://git.kernel.dk/linux-block	2017-03-03 10:53:35 -08:00
certs	certs: Add a secondary system keyring that can be added to dynamically	2016-04-11 22:48:09 +01:00
crypto	Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6	2017-03-04 10:42:53 -08:00
Documentation	A few fixes for the docs tree, including one for a 4.11 build regression.	2017-03-04 11:32:18 -08:00
drivers	Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net	2017-03-04 17:31:39 -08:00
firmware	WHENCE: use https://linuxtv.org for LinuxTV URLs	2015-12-04 10:35:11 -02:00
fs	iomap: invalidate page caches should be after iomap_dio_complete() in direct write	2017-03-06 09:50:01 -08:00
include	Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net	2017-03-04 17:31:39 -08:00
init	sched/headers: Prepare to move _init() prototypes from <linux/sched.h> to <linux/sched/init.h>	2017-03-02 08:42:40 +01:00
ipc	Merge branch 'WIP.sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip	2017-03-03 10:16:38 -08:00
kernel	Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net	2017-03-04 17:31:39 -08:00
lib	Merge branch 'WIP.sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip	2017-03-03 10:16:38 -08:00
mm	Merge branch 'rebased-statx' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs	2017-03-03 11:38:56 -08:00
net	Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net	2017-03-04 17:31:39 -08:00
samples	Merge branch 'rebased-statx' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs	2017-03-03 11:38:56 -08:00
scripts	objtool, modules: Discard objtool annotation sections for modules	2017-03-01 20:32:25 +01:00
security	Merge branch 'WIP.sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip	2017-03-03 10:16:38 -08:00
sound	sched/headers: Prepare to move signal wakeup & sigpending methods from <linux/sched.h> into <linux/sched/signal.h>	2017-03-02 08:42:32 +01:00
tools	Second batch of KVM changes for 4.11 merge window	2017-03-04 11:36:19 -08:00
usr	kbuild: initramfs cleanup, set target from Kconfig	2017-01-05 09:40:16 -08:00
virt	Second batch of KVM changes for 4.11 merge window	2017-03-04 11:36:19 -08:00
.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	Merge branch 'misc' of git://git.kernel.org/pub/scm/linux/kernel/git/mmarek/kbuild	2016-08-02 16:48:52 -04:00
.mailmap	mailmap: add codeaurora.org names for nameless email commits	2017-01-10 18:31:55 -08:00
COPYING
CREDITS	MAINTAINERS: Remove old e-mail address	2017-02-13 12:24:56 -05:00
Kbuild	scripts/gdb: provide linux constants	2016-05-23 17:04:14 -07:00
Kconfig
MAINTAINERS	Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net	2017-03-04 17:31:39 -08:00
Makefile	Linux 4.11-rc1	2017-03-05 12:59:56 -08:00
README	README: add a new README file, pointing to the Documentation/	2016-10-24 08:12:35 -02:00

README

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.