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Filipe Manana 505a948d05 btrfs: do not delete unused block group if it may be used soon 
commit f4a9f21941 upstream.

Before deleting a block group that is in the list of unused block groups
(fs_info->unused_bgs), we check if the block group became used before
deleting it, as extents from it may have been allocated after it was added
to the list.

However even if the block group was not yet used, there may be tasks that
have only reserved space and have not yet allocated extents, and they
might be relying on the availability of the unused block group in order
to allocate extents. The reservation works first by increasing the
"bytes_may_use" field of the corresponding space_info object (which may
first require flushing delayed items, allocating a new block group, etc),
and only later a task does the actual allocation of extents.

For metadata we usually don't end up using all reserved space, as we are
pessimistic and typically account for the worst cases (need to COW every
single node in a path of a tree at maximum possible height, etc). For
data we usually reserve the exact amount of space we're going to allocate
later, except when using compression where we always reserve space based
on the uncompressed size, as compression is only triggered when writeback
starts so we don't know in advance how much space we'll actually need, or
if the data is compressible.

So don't delete an unused block group if the total size of its space_info
object minus the block group's size is less then the sum of used space and
space that may be used (space_info->bytes_may_use), as that means we have
tasks that reserved space and may need to allocate extents from the block
group. In this case, besides skipping the deletion, re-add the block group
to the list of unused block groups so that it may be reconsidered later,
in case the tasks that reserved space end up not needing to allocate
extents from it.

Allowing the deletion of the block group while we have reserved space, can
result in tasks failing to allocate metadata extents (-ENOSPC) while under
a transaction handle, resulting in a transaction abort, or failure during
writeback for the case of data extents.

CC: stable@vger.kernel.org # 6.0+
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2024-02-23 09:24:47 +01:00
arch work around gcc bugs with 'asm goto' with outputs 2024-02-23 09:24:47 +01:00
block blk-iocost: Fix an UBSAN shift-out-of-bounds warning 2024-02-16 19:10:53 +01:00
certs certs: Reference revocation list for all keyrings 2023-08-17 20:12:41 +00:00
crypto crypto: api - Disallow identical driver names 2024-01-31 16:18:49 -08:00
Documentation rust: upgrade to Rust 1.73.0 2024-02-16 19:10:43 +01:00
drivers net: stmmac: xgmac: fix a typo of register name in DPP safety handling 2024-02-16 19:10:57 +01:00
fs btrfs: do not delete unused block group if it may be used soon 2024-02-23 09:24:47 +01:00
include update workarounds for gcc "asm goto" issue 2024-02-23 09:24:47 +01:00
init update workarounds for gcc "asm goto" issue 2024-02-23 09:24:47 +01:00
io_uring io_uring/net: limit inline multishot retries 2024-02-16 19:10:56 +01:00
ipc Add x86 shadow stack support 2023-08-31 12:20:12 -07:00
kernel hrtimer: Report offline hrtimer enqueue 2024-02-16 19:10:55 +01:00
lib kunit: run test suites only after module initialization completes 2024-02-05 20:14:34 +00:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm mm: Introduce flush_cache_vmap_early() 2024-02-16 19:10:52 +01:00
net work around gcc bugs with 'asm goto' with outputs 2024-02-23 09:24:47 +01:00
rust rust: upgrade to Rust 1.73.0 2024-02-16 19:10:43 +01:00
samples work around gcc bugs with 'asm goto' with outputs 2024-02-23 09:24:47 +01:00
scripts rust: upgrade to Rust 1.73.0 2024-02-16 19:10:43 +01:00
security lsm: new security_file_ioctl_compat() hook 2024-01-31 16:18:54 -08:00
sound ALSA: usb-audio: Sort quirk table entries 2024-02-16 19:10:56 +01:00
tools work around gcc bugs with 'asm goto' with outputs 2024-02-23 09:24:47 +01:00
usr initramfs: Encode dependency on KBUILD_BUILD_TIMESTAMP 2023-06-06 17:54:49 +09:00
virt ARM: 2023-09-07 13:52:20 -07:00
.clang-format iommu: Add for_each_group_device() 2023-05-23 08:15:51 +02:00
.cocciconfig
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore kbuild: rpm-pkg: rename binkernel.spec to kernel.spec 2023-07-25 00:59:33 +09:00
.mailmap 20 hotfixes. 12 are cc:stable and the remainder address post-6.5 issues 2023-10-24 09:52:16 -10:00
.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 USB: Remove Wireless USB and UWB documentation 2023-08-09 14:17:32 +02:00
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 MAINTAINERS: add Catherine as xfs maintainer for 6.6.y 2024-02-16 19:10:43 +01:00
Makefile Linux 6.6.17 2024-02-16 19:10:57 +01:00
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.