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Boris Burkov 7a2339058e btrfs: fix read corruption due to race with extent map merging 
In debugging some corrupt squashfs files, we observed symptoms of
corrupt page cache pages but correct on-disk contents. Further
investigation revealed that the exact symptom was a correct page
followed by an incorrect, duplicate, page. This got us thinking about
extent maps.

commit ac05ca913e ("Btrfs: fix race between using extent maps and merging them")
enforces a reference count on the primary `em` extent_map being merged,
as that one gets modified.

However, since,
commit 3d2ac99224 ("btrfs: introduce new members for extent_map")
both 'em' and 'merge' get modified, which started modifying 'merge'
and thus introduced the same race.

We were able to reproduce this by looping the affected squashfs workload
in parallel on a bunch of separate btrfs-es while also dropping caches.
We are still working on a simple enough reproducer to make into an fstest.

The simplest fix is to stop modifying 'merge', which is not essential,
as it is dropped immediately after the merge. This behavior is simply
a consequence of the order of the two extent maps being important in
computing the new values. Modify merge_ondisk_extents to take prev and
next by const* and also take a third merged parameter that it puts the
results in. Note that this introduces the rather odd behavior of passing
'em' to merge_ondisk_extents as a const * and as a regular ptr.

Fixes: 3d2ac99224 ("btrfs: introduce new members for extent_map")
CC: stable@vger.kernel.org # 6.11+
Reviewed-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Boris Burkov <boris@bur.io>
Signed-off-by: David Sterba <dsterba@suse.com>
2024-10-22 16:10:13 +02:00
arch KVM: x86: don't fall through case statements without annotations 2024-09-06 15:23:33 -07:00
block bio-integrity: don't restrict the size of integrity metadata 2024-09-04 07:17:00 -06:00
certs kbuild: use $(src) instead of $(srctree)/$(src) for source directory 2024-05-10 04:34:52 +09:00
crypto crypto: testmgr - generate power-of-2 lengths more often 2024-07-13 11:50:28 +12:00
Documentation Char/Misc driver fixes for 6.11-rc7 2024-09-08 10:13:39 -07:00
drivers - Remove percpu irq related code in the timer-of initialization 2024-09-08 10:25:25 -07:00
fs btrfs: fix read corruption due to race with extent map merging 2024-10-22 16:10:13 +02:00
include btrfs: tracepoints: end assignment with semicolon at btrfs_qgroup_extent event class 2024-10-01 19:14:10 +02:00
init Rust fixes for v6.11 2024-08-16 11:24:06 -07:00
io_uring io_uring/kbuf: return correct iovec count from classic buffer peek 2024-08-30 10:45:54 -06:00
ipc sysctl: treewide: constify the ctl_table argument of proc_handlers 2024-07-24 20:59:29 +02:00
kernel - Fix perf's AUX buffer serialization 2024-09-08 10:20:44 -07:00
lib linux_kselftest-kunit-fixes-6.11-rc7 2024-09-05 09:43:38 -07:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm vfs-6.11-rc7.fixes 2024-09-04 09:33:57 -07:00
net ila: call nf_unregister_net_hooks() sooner 2024-09-05 14:57:12 -07:00
rust rust: macros: provide correct provenance when constructing THIS_MODULE 2024-09-02 09:14:28 +02:00
samples treewide: remove unnecessary <linux/version.h> inclusion 2024-08-12 18:36:44 +09:00
scripts scripts: fix gfp-translate after ___GFP_*_BITS conversion to an enum 2024-09-01 17:59:01 -07:00
security Merge branch 'fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/groeck/linux-staging 2024-09-01 09:18:48 +12:00
sound sound fixes for 6.11-rc7 2024-09-06 11:56:03 -07:00
tools RISC-V Fixes for 6.11-rc7 2024-09-06 13:00:59 -07:00
usr initramfs: shorten cmd_initfs in usr/Makefile 2024-07-16 01:07:52 +09:00
virt KVM: x86: Disallow read-only memslots for SEV-ES and SEV-SNP (and TDX) 2024-08-14 12:28:24 -04:00
.clang-format Docs: Move clang-format from process/ to dev-tools/ 2024-06-26 16:36:00 -06:00
.cocciconfig
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore kbuild: add script and target to generate pacman package 2024-07-22 01:24:22 +09:00
.mailmap Rust fixes for v6.11 (2nd) 2024-09-05 16:35:57 -07:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS tracing: Update of MAINTAINERS and CREDITS file 2024-07-18 14:08:42 -07:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS drm fixes for 6.11-rc7 2024-09-06 11:15:40 -07:00
Makefile Linux 6.11-rc7 2024-09-08 14:50:28 -07:00
README README: Fix spelling 2024-03-18 03:36:32 -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 reStructuredText 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.