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Michal Hocko 97beeb6ff4 mm, percpu: do not consider sleepable allocations atomic 
[ Upstream commit 9a5b183941 ]

28307d938f ("percpu: make pcpu_alloc() aware of current gfp context")
has fixed a reclaim recursion for scoped GFP_NOFS context.  It has done
that by avoiding taking pcpu_alloc_mutex.  This is a correct solution as
the worker context with full GFP_KERNEL allocation/reclaim power and which
is using the same lock cannot block the NOFS pcpu_alloc caller.

On the other hand this is a very conservative approach that could lead to
failures because pcpu_alloc lockless implementation is quite limited.

We have a bug report about premature failures when scsi array of 193
devices is scanned.  Sometimes (not consistently) the scanning aborts
because the iscsid daemon fails to create the queue for a random scsi
device during the scan.  iscsid itself is running with PR_SET_IO_FLUSHER
set so all allocations from this process context are GFP_NOIO.  This in
turn makes any pcpu_alloc lockless (without pcpu_alloc_mutex) which leads
to pre-mature failures.

It has turned out that iscsid has worked around this by dropping
PR_SET_IO_FLUSHER (https://github.com/open-iscsi/open-iscsi/pull/382) when
scanning host.  But we can do better in this case on the kernel side and
use pcpu_alloc_mutex for NOIO resp.  NOFS constrained allocation scopes
too.  We just need the WQ worker to never trigger IO/FS reclaim.  Achieve
that by enforcing scoped GFP_NOIO for the whole execution of
pcpu_balance_workfn (this will imply NOFS constrain as well).  This will
remove the dependency chain and preserve the full allocation power of the
pcpu_alloc call.

While at it make is_atomic really test for blockable allocations.

Link: https://lkml.kernel.org/r/20250206122633.167896-1-mhocko@kernel.org
Fixes: 28307d938f ("percpu: make pcpu_alloc() aware of current gfp context")
Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Filipe David Manana <fdmanana@suse.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: chenxin <chenxinxin@xiaomi.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2025-12-07 06:12:36 +09:00
arch KVM: SVM: Mark VMCB_LBR dirty when MSR_IA32_DEBUGCTLMSR is updated 2025-12-07 06:12:36 +09:00
block block: fix race between set_blocksize and read paths 2025-12-07 06:12:14 +09:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2025-04-25 10:44:04 +02:00
crypto crypto: essiv - Check ssize for decryption and in-place encryption 2025-10-19 16:23:10 +02:00
Documentation xhci: dbc: Allow users to modify DbC poll interval via sysfs 2025-12-07 06:12:10 +09:00
drivers iommufd: Don't overflow during division for dirty tracking 2025-12-07 06:12:36 +09:00
fs eventpoll: Replace rwlock with spinlock 2025-12-07 06:12:36 +09:00
include scsi: ufs: core: Add a quirk to suppress link_startup_again 2025-12-07 06:12:36 +09:00
init init: handle bootloader identifier in kernel parameters 2025-10-19 16:23:13 +02:00
io_uring io_uring: correct __must_hold annotation in io_install_fixed_file 2025-10-29 14:04:38 +01:00
ipc ipc: fix to protect IPCS lookups using RCU 2025-06-27 11:07:30 +01:00
kernel gcov: add support for GCC 15 2025-12-07 06:12:35 +09:00
lib lib/crypto: curve25519-hacl64: Fix older clang KASAN workaround for GCC 2025-12-07 06:12:30 +09:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
mm mm, percpu: do not consider sleepable allocations atomic 2025-12-07 06:12:36 +09:00
net net: netpoll: fix incorrect refcount handling causing incorrect cleanup 2025-12-07 06:12:36 +09:00
rust mm/ksm: fix flag-dropping behavior in ksm_madvise 2025-10-29 14:04:43 +01:00
samples ftrace/samples: Fix function size computation 2025-09-19 16:29:56 +02:00
scripts gcc-plugins: Remove TODO_verify_il for GCC >= 16 2025-10-15 11:56:20 +02:00
security KEYS: trusted_tpm1: Compare HMAC values in constant time 2025-10-19 16:23:14 +02:00
sound ALSA: usb-audio: Fix missing unlock at error path of maxpacksize check 2025-12-07 06:12:35 +09:00
tools selftests: mptcp: connect: trunc: read all recv data 2025-12-07 06:12:36 +09:00
usr kbuild: uapi: Strip comments before size type check 2025-12-07 06:12:28 +09:00
virt KVM: Fix a data race on last_boosted_vcpu in kvm_vcpu_on_spin() 2024-06-27 13:46:21 +02:00
.clang-format inet: ping: use hlist_nulls rcu iterator during lookup 2022-12-01 12:42:46 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore Remove *.orig pattern from .gitignore 2024-10-17 15:21:15 +02:00
.mailmap 9 hotfixes. 6 for MM, 3 for other areas. Four of these patches address 2022-12-10 17:10:52 -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 Michal Marek from Kbuild maintainers 2022-11-16 14:53:00 +09:00
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 netdevsim: add Makefile for selftests 2025-12-07 06:12:29 +09:00
Makefile Linux 6.1.158 2025-10-29 14:04:43 +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.