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Junbeom Yeom 28a6c420f0 erofs: fix unexpected EIO under memory pressure 
commit 4012d78562 upstream.

erofs readahead could fail with ENOMEM under the memory pressure because
it tries to alloc_page with GFP_NOWAIT | GFP_NORETRY, while GFP_KERNEL
for a regular read. And if readahead fails (with non-uptodate folios),
the original request will then fall back to synchronous read, and
`.read_folio()` should return appropriate errnos.

However, in scenarios where readahead and read operations compete,
read operation could return an unintended EIO because of an incorrect
error propagation.

To resolve this, this patch modifies the behavior so that, when the
PCL is for read(which means pcl.besteffort is true), it attempts actual
decompression instead of propagating the privios error except initial EIO.

- Page size: 4K
- The original size of FileA: 16K
- Compress-ratio per PCL: 50% (Uncompressed 8K -> Compressed 4K)
[page0, page1] [page2, page3]
[PCL0]---------[PCL1]

- functions declaration:
  . pread(fd, buf, count, offset)
  . readahead(fd, offset, count)
- Thread A tries to read the last 4K
- Thread B tries to do readahead 8K from 4K
- RA, besteffort == false
- R, besteffort == true

        <process A>                   <process B>

pread(FileA, buf, 4K, 12K)
  do readahead(page3) // failed with ENOMEM
  wait_lock(page3)
    if (!uptodate(page3))
      goto do_read
                               readahead(FileA, 4K, 8K)
                               // Here create PCL-chain like below:
                               // [null, page1] [page2, null]
                               //   [PCL0:RA]-----[PCL1:RA]
...
  do read(page3)        // found [PCL1:RA] and add page3 into it,
                        // and then, change PCL1 from RA to R
...
                               // Now, PCL-chain is as below:
                               // [null, page1] [page2, page3]
                               //   [PCL0:RA]-----[PCL1:R]

                                 // try to decompress PCL-chain...
                                 z_erofs_decompress_queue
                                   err = 0;

                                   // failed with ENOMEM, so page 1
                                   // only for RA will not be uptodated.
                                   // it's okay.
                                   err = decompress([PCL0:RA], err)

                                   // However, ENOMEM propagated to next
                                   // PCL, even though PCL is not only
                                   // for RA but also for R. As a result,
                                   // it just failed with ENOMEM without
                                   // trying any decompression, so page2
                                   // and page3 will not be uptodated.
                ** BUG HERE ** --> err = decompress([PCL1:R], err)

                                   return err as ENOMEM
...
    wait_lock(page3)
      if (!uptodate(page3))
        return EIO      <-- Return an unexpected EIO!
...

Fixes: 2349d2fa02 ("erofs: sunset unneeded NOFAILs")
Cc: stable@vger.kernel.org
Reviewed-by: Jaewook Kim <jw5454.kim@samsung.com>
Reviewed-by: Sungjong Seo <sj1557.seo@samsung.com>
Signed-off-by: Junbeom Yeom <junbeom.yeom@samsung.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2026-01-08 10:17:20 +01:00
arch LoongArch: BPF: Adjust the jump offset of tail calls 2026-01-08 10:17:13 +01:00
block block: Clear BLK_ZONE_WPLUG_PLUGGED when aborting plugged BIOs 2026-01-08 10:16:58 +01:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: seqiv - Do not use req->iv after crypto_aead_encrypt 2026-01-08 10:16:43 +01:00
Documentation dt-bindings: PCI: qcom,pcie-sm8550: Add missing required power-domains and resets 2026-01-02 12:57:27 +01:00
drivers drm/imagination: Disallow exporting of PM/FW protected objects 2026-01-08 10:17:20 +01:00
fs erofs: fix unexpected EIO under memory pressure 2026-01-08 10:17:20 +01:00
include drm/pagemap, drm/xe: Ensure that the devmem allocation is idle before use 2026-01-08 10:17:20 +01:00
init printk changes for 6.18 2025-10-04 11:13:11 -07:00
io_uring io_uring/rsrc: fix lost entries after cloned range 2026-01-02 12:57:30 +01:00
ipc namespace-6.18-rc1 2025-09-29 11:20:29 -07:00
kernel kernel/kexec: fix IMA when allocation happens in CMA area 2026-01-08 10:17:10 +01:00
lib idr: fix idr_alloc() returning an ID out of range 2026-01-08 10:17:10 +01:00
LICENSES LICENSES: Replace the obsolete address of the FSF in the GFDL-1.2 2025-07-24 11:15:39 +02:00
mm mm/page_owner: fix memory leak in page_owner_stack_fops->release() 2026-01-08 10:17:10 +01:00
net net: nfc: fix deadlock between nfc_unregister_device and rfkill_fop_write 2026-01-08 10:17:14 +01:00
rust rust: maple_tree: rcu_read_lock() in destructor to silence lockdep 2026-01-08 10:17:11 +01:00
samples samples/ftrace: Adjust LoongArch register restore order in direct calls 2026-01-08 10:17:11 +01:00
scripts mcb: Add missing modpost build support 2026-01-08 10:16:47 +01:00
security kernel/kexec: change the prototype of kimage_map_segment() 2026-01-08 10:17:10 +01:00
sound ASoC: qcom: qdsp6: q6asm-dai: set 10 ms period and buffer alignment. 2026-01-08 10:16:54 +01:00
tools selftests/mm: fix thread state check in uffd-unit-tests 2026-01-08 10:17:11 +01:00
usr gen_init_cpio: Ignore fsync() returning EINVAL on pipes 2025-10-07 09:53:05 -07:00
virt KVM: Fix last_boosted_vcpu index assignment bug 2026-01-02 12:57:21 +01:00
.clang-format memblock: drop for_each_free_mem_pfn_range_in_zone_from() 2025-09-14 08:49:03 +03:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-07 00:11:47 +02:00
.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 MAINTAINERS: remove Alyssa Rosenzweig 2025-09-18 21:17:31 +02:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore .gitignore: ignore compile_commands.json globally 2025-08-12 15:53:55 -07:00
.mailmap 8 hotfixes. 4 are cc:stable, 7 are against mm/. 2025-11-26 12:38:05 -08:00
.pylintrc tools: docs: parse-headers.py: move it from sphinx dir 2025-08-29 15:54:42 -06:00
.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: mark ISDN subsystem as orphan 2025-10-27 17:49:45 -07:00
Kbuild sched: Make migrate_{en,dis}able() inline 2025-09-25 09:57:16 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS soc: fixes for 6.18, part 4 2025-11-28 09:57:31 -08:00
Makefile Linux 6.18.3 2026-01-02 12:57:31 +01:00
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.