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Raphael S. Carvalho 182db972c9 mm: fix error handling in __filemap_get_folio() with FGP_NOWAIT
original report:
https://lore.kernel.org/all/CAKhLTr1UL3ePTpYjXOx2AJfNk8Ku2EdcEfu+CH1sf3Asr=B-Dw@mail.gmail.com/T/

When doing buffered writes with FGP_NOWAIT, under memory pressure, the
system returned ENOMEM despite there being plenty of available memory, to
be reclaimed from page cache.  The user space used io_uring interface,
which in turn submits I/O with FGP_NOWAIT (the fast path).

retsnoop pointed to iomap_get_folio:

00:34:16.180612 -> 00:34:16.180651 TID/PID 253786/253721
(reactor-1/combined_tests):

                    entry_SYSCALL_64_after_hwframe+0x76
                    do_syscall_64+0x82
                    __do_sys_io_uring_enter+0x265
                    io_submit_sqes+0x209
                    io_issue_sqe+0x5b
                    io_write+0xdd
                    xfs_file_buffered_write+0x84
                    iomap_file_buffered_write+0x1a6
    32us [-ENOMEM]  iomap_write_begin+0x408
iter=&{.inode=0xffff8c67aa031138,.len=4096,.flags=33,.iomap={.addr=0xffffffffffffffff,.length=4096,.type=1,.flags=3,.bdev=0x…
pos=0 len=4096 foliop=0xffffb32c296b7b80
!    4us [-ENOMEM]  iomap_get_folio
iter=&{.inode=0xffff8c67aa031138,.len=4096,.flags=33,.iomap={.addr=0xffffffffffffffff,.length=4096,.type=1,.flags=3,.bdev=0x…
pos=0 len=4096

This is likely a regression caused by 66dabbb65d ("mm: return an ERR_PTR
from __filemap_get_folio"), which moved error handling from
io_map_get_folio() to __filemap_get_folio(), but broke FGP_NOWAIT
handling, so ENOMEM is being escaped to user space.  Had it correctly
returned -EAGAIN with NOWAIT, either io_uring or user space itself would
be able to retry the request.

It's not enough to patch io_uring since the iomap interface is the one
responsible for it, and pwritev2(RWF_NOWAIT) and AIO interfaces must
return the proper error too.

The patch was tested with scylladb test suite (its original reproducer),
and the tests all pass now when memory is pressured.

Link: https://lkml.kernel.org/r/20250224143700.23035-1-raphaelsc@scylladb.com
Fixes: 66dabbb65d ("mm: return an ERR_PTR from __filemap_get_folio")
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Cc: "Darrick J. Wong" <djwong@kernel.org>
Cc: Matthew Wilcow (Oracle) <willy@infradead.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2025-03-16 17:40:25 -07:00
arch KVM/arm64 fixes for 6.14, take #4 2025-03-09 09:04:08 -10:00
block block-6.14-20250306 2025-03-07 11:12:33 -10:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto treewide: const qualify ctl_tables where applicable 2025-01-28 13:48:37 +01:00
Documentation Kbuild fixes for v6.14 (3rd) 2025-03-09 09:23:14 -10:00
drivers USB fixes for 6.14-rc6 2025-03-09 09:14:07 -10:00
fs squashfs: fix invalid pointer dereference in squashfs_cache_delete 2025-03-16 17:40:24 -07:00
include mm: memcontrol: fix swap counter leak from offline cgroup 2025-03-16 17:40:24 -07:00
init Kbuild updates for v6.14 2025-01-31 12:07:07 -08:00
io_uring io_uring-6.14-20250306 2025-03-07 11:09:33 -10:00
ipc treewide: const qualify ctl_tables where applicable 2025-01-28 13:48:37 +01:00
kernel Miscellaneous scheduler fixes: 2025-03-07 10:58:54 -10:00
lib 33 hotfixes. 24 are cc:stable and the remainder address post-6.13 issues 2025-03-08 14:34:06 -10:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm mm: fix error handling in __filemap_get_folio() with FGP_NOWAIT 2025-03-16 17:40:25 -07:00
net net: ipv6: fix missing dst ref drop in ila lwtunnel 2025-03-06 11:08:45 +01:00
rust Driver core api addition for 6.14-rc3 2025-02-16 12:54:42 -08:00
samples Driver core api addition for 6.14-rc3 2025-02-16 12:54:42 -08:00
scripts kbuild: install-extmod-build: Fix build when specifying KBUILD_OUTPUT 2025-03-06 20:32:30 +09:00
security Landlock fix for v6.14-rc5 2025-02-26 11:55:44 -08:00
sound ALSA: hda/realtek: Add support for ASUS Zenbook UM3406KA Laptops using CS35L41 HDA 2025-03-05 19:52:56 +01:00
tools KVM/arm64 fixes for 6.14, take #4 2025-03-09 09:04:08 -10:00
usr kbuild: hdrcheck: fix cross build with clang 2025-03-05 04:06:45 +09:00
virt KVM: remove kvm_arch_post_init_vm 2025-02-04 11:27:45 -05:00
.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 2025-01-10 00:17:25 +01:00
.cocciconfig
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore MAINTAINERS: Retire Ralf Baechle 2024-11-12 15:48:59 +01:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore rust: use host dylib naming convention to support macOS 2025-01-10 01:01:24 +01:00
.mailmap 33 hotfixes. 24 are cc:stable and the remainder address post-6.13 issues 2025-03-08 14:34:06 -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 MAINTAINERS: Move Pavel to kernel.org address 2025-02-07 09:12:33 -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 Char/Misc/IIO driver fixes for 6.14-rc6 2025-03-09 09:07:54 -10:00
Makefile Linux 6.14-rc6 2025-03-09 13:45:25 -10:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

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.