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Qu Wenruo 820cfaee9d btrfs: fix the incorrect max_bytes value for find_lock_delalloc_range() 
[ Upstream commit 7b26da4074 ]

[BUG]
With my local branch to enable bs > ps support for btrfs, sometimes I
hit the following ASSERT() inside submit_one_sector():

	ASSERT(block_start != EXTENT_MAP_HOLE);

Please note that it's not yet possible to hit this ASSERT() in the wild
yet, as it requires btrfs bs > ps support, which is not even in the
development branch.

But on the other hand, there is also a very low chance to hit above
ASSERT() with bs < ps cases, so this is an existing bug affect not only
the incoming bs > ps support but also the existing bs < ps support.

[CAUSE]
Firstly that ASSERT() means we're trying to submit a dirty block but
without a real extent map nor ordered extent map backing it.

Furthermore with extra debugging, the folio triggering such ASSERT() is
always larger than the fs block size in my bs > ps case.
(8K block size, 4K page size)

After some more debugging, the ASSERT() is trigger by the following
sequence:

 extent_writepage()
 |  We got a 32K folio (4 fs blocks) at file offset 0, and the fs block
 |  size is 8K, page size is 4K.
 |  And there is another 8K folio at file offset 32K, which is also
 |  dirty.
 |  So the filemap layout looks like the following:
 |
 |  "||" is the filio boundary in the filemap.
 |  "//| is the dirty range.
 |
 |  0        8K       16K        24K         32K       40K
 |  |////////|        |//////////////////////||////////|
 |
 |- writepage_delalloc()
 |  |- find_lock_delalloc_range() for [0, 8K)
 |  |  Now range [0, 8K) is properly locked.
 |  |
 |  |- find_lock_delalloc_range() for [16K, 40K)
 |  |  |- btrfs_find_delalloc_range() returned range [16K, 40K)
 |  |  |- lock_delalloc_folios() locked folio 0 successfully
 |  |  |
 |  |  |  The filemap range [32K, 40K) got dropped from filemap.
 |  |  |
 |  |  |- lock_delalloc_folios() failed with -EAGAIN on folio 32K
 |  |  |  As the folio at 32K is dropped.
 |  |  |
 |  |  |- loops = 1;
 |  |  |- max_bytes = PAGE_SIZE;
 |  |  |- goto again;
 |  |  |  This will re-do the lookup for dirty delalloc ranges.
 |  |  |
 |  |  |- btrfs_find_delalloc_range() called with @max_bytes == 4K
 |  |  |  This is smaller than block size, so
 |  |  |  btrfs_find_delalloc_range() is unable to return any range.
 |  |  \- return false;
 |  |
 |  \- Now only range [0, 8K) has an OE for it, but for dirty range
 |     [16K, 32K) it's dirty without an OE.
 |     This breaks the assumption that writepage_delalloc() will find
 |     and lock all dirty ranges inside the folio.
 |
 |- extent_writepage_io()
    |- submit_one_sector() for [0, 8K)
    |  Succeeded
    |
    |- submit_one_sector() for [16K, 24K)
       Triggering the ASSERT(), as there is no OE, and the original
       extent map is a hole.

Please note that, this also exposed the same problem for bs < ps
support. E.g. with 64K page size and 4K block size.

If we failed to lock a folio, and falls back into the "loops = 1;"
branch, we will re-do the search using 64K as max_bytes.
Which may fail again to lock the next folio, and exit early without
handling all dirty blocks inside the folio.

[FIX]
Instead of using the fixed size PAGE_SIZE as @max_bytes, use
@sectorsize, so that we are ensured to find and lock any remaining
blocks inside the folio.

And since we're here, add an extra ASSERT() to
before calling btrfs_find_delalloc_range() to make sure the @max_bytes is
at least no smaller than a block to avoid false negative.

Cc: stable@vger.kernel.org # 5.15+
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2025-10-19 16:34:02 +02:00
arch s390: Add -Wno-pointer-sign to KBUILD_CFLAGS_DECOMPRESSOR 2025-10-19 16:33:57 +02:00
block blk-crypto: fix missing blktrace bio split events 2025-10-19 16:33:48 +02:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: essiv - Check ssize for decryption and in-place encryption 2025-10-19 16:33:42 +02:00
Documentation dt-bindings: phy: rockchip-inno-csi-dphy: make power-domains non-required 2025-10-19 16:33:45 +02:00
drivers mfd: intel_soc_pmic_chtdc_ti: Set use_single_read regmap_config flag 2025-10-19 16:34:02 +02:00
fs btrfs: fix the incorrect max_bytes value for find_lock_delalloc_range() 2025-10-19 16:34:02 +02:00
include mm/ksm: fix incorrect KSM counter handling in mm_struct during fork 2025-10-19 16:34:01 +02:00
init init: handle bootloader identifier in kernel parameters 2025-10-19 16:33:50 +02:00
io_uring io_uring/waitid: always prune wait queue entry in io_waitid_wait() 2025-10-15 12:00:20 +02:00
ipc ipc: fix to protect IPCS lookups using RCU 2025-06-27 11:11:22 +01:00
kernel tracing: Fix race condition in kprobe initialization causing NULL pointer dereference 2025-10-19 16:34:01 +02:00
lib lib/crypto/curve25519-hacl64: Disable KASAN with clang-17 and older 2025-10-19 16:34:00 +02:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm mm/damon/lru_sort: use param_ctx for damon_attrs staging 2025-10-19 16:33:58 +02:00
net xsk: Harden userspace-supplied xdp_desc validation 2025-10-19 16:33:53 +02:00
rust rust: block: fix srctree/ links 2025-10-12 12:57:16 +02:00
samples ftrace/samples: Fix function size computation 2025-09-19 16:35:44 +02:00
scripts gcc-plugins: Remove TODO_verify_il for GCC >= 16 2025-10-06 11:17:52 +02:00
security KEYS: trusted_tpm1: Compare HMAC values in constant time 2025-10-19 16:33:51 +02:00
sound ASoC: SOF: ipc4-pcm: fix delay calculation when DSP resamples 2025-10-19 16:34:01 +02:00
tools selftests/mm: skip soft-dirty tests when CONFIG_MEM_SOFT_DIRTY is disabled 2025-10-19 16:34:00 +02:00
usr kbuild: hdrcheck: fix cross build with clang 2025-03-13 13:02:18 +01:00
virt KVM: Allow CPU to reschedule while setting per-page memory attributes 2025-07-17 18:37:08 +02:00
.clang-format clang-format: Update with v6.11-rc1's for_each macro list 2024-08-02 13:20:31 +02:00
.clippy.toml rust: give Clippy the minimum supported Rust version 2025-08-01 09:48:44 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.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 rust: introduce .clippy.toml 2025-03-13 13:01:42 +01:00
.mailmap mailmap: add entry for Thorsten Blum 2024-11-07 14:14:59 -08:00
.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 MAINTAINERS: Remove self from DSA entry 2024-11-03 12:52:38 -08:00
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: Update Alexey Makhalov's email address 2025-05-22 14:29:46 +02:00
Makefile Linux 6.12.53 2025-10-15 12:00:25 +02:00
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.