FAILED: patch "[PATCH] mips: select CONFIG_WEAK_REORDERING_BEYOND_LLSC from" failed to apply to 6.18-stable tree
Subsystems (2)
[email protected]
maintainerThe patch below does not apply to the 6.18-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.
To reproduce the conflict and resubmit, you may use the following commands:
git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x bbc448c541ed90d52f9ec22f17394304e3bf170e
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026092205-ipod-uncloak-9772@gregkh' --subject-prefix 'PATCH 6.18.y' 'HEAD^..'
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From bbc448c541ed90d52f9ec22f17394304e3bf170e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Th=C3=A9o=20Lebrun?= <[email protected]>
Date: Fri, 28 Aug 2026 16:07:33 +0200
Subject: [PATCH] mips: select CONFIG_WEAK_REORDERING_BEYOND_LLSC from
CONFIG_EYEQ
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On I6500 CPU cores, lld and scd give no ordering guarantees (same as all other instructions). To respect the assumption that arch_cmpxchg() is fully ordered, we must inject sync instructions above and below our lld/scd loops using the already in place WEAK_REORDERING_BEYOND_LLSC infrastructure.
Otherwise, bad things can happen:
[ 34.054496] CPU 3 Unable to handle kernel paging request at virtual address 0000000000000000, epc == a80000080838e01c, ra == a80000080838dfc4 [ 34.054559] Oops[#1]: [ 34.069561] CPU: 3 UID: 0 PID: 170 Comm: pipe_race Not tainted 7.2.0-rc6-01553-gb73c35220968-dirty #103 VOLUNTARY [ 34.079932] Hardware name: Mobile EyeQ5 MP5 Evaluation board [ 34.085592] $ 0 : 0000000000000000 0000000000000001 0000000000000000 0000000000000000 [ 34.093616] $ 4 : a800000808ee2618 000000000b7a879d 0000000000001000 0000000000000000 [ 34.101638] $ 8 : 0000000000e3f2c9 0000000000000000 a800000808a2a9f8 0000000000000000 [ 34.109660] $12 : a8000008139ffcd8 ffffffff84080018 a80000080837fae0 7878787878787878 [ 34.117682] $16 : a800000807e82940 0000000000001000 0000000000000000 0000000000000000 [ 34.125704] $20 : a800000802920e00 a8000008139ffdf8 a800000802649400 0000000000e3f2c9 [ 34.133726] $24 : 0000000000000006 00000001200406e0 [ 34.141783] $28 : a8000008139fc000 a8000008139ffd10 0000000000e3f2c8 a80000080838dfc4 [ 34.149837] epc : a80000080838e01c anon_pipe_read+0xd4/0x428 [ 34.155697] ra : a80000080838dfc4 anon_pipe_read+0x7c/0x428 [ 34.161549] Status: 140000e3 KX SX UX KERNEL EXL IE [ 34.166551] Cause : 40800408 (ExcCode 02) [ 34.170574] BadVA : 0000000000000000 [ 34.174161] PrId : 0001b028 (MIPS I6500) [ 34.178183] Process pipe_race (pid: 170, threadinfo=000000005ca35720, task=00000000e1013890, tls=000000014ebbb780) [ 34.188568] Stack : a800000802649400 0000000000000000 0000000000000000 a8000008139ffdd0 [ 34.196623] 0000000000000fba a800000808ee0000 0000000000000001 a8000008130c3e80 [ 34.204676] a8000008080d1280 a8000008139ffd58 a8000008139ffd58 1dbd2b22ea1dd500 [ 34.212729] a800000802649400 a800000808ee0000 ffffffffffffffea 0000000000000001 [ 34.220783] 0000000000001000 0000000000000000 00000001200ae518 ffffffffffffffff [ 34.228836] 000000fffbe0e530 a80000080837edf4 000000fffbe0e530 0000000000000000 [ 34.236890] 0000000000000000 0000000000000000 000000014ebb55a0 0000000000001000 [ 34.244943] 0000000000000001 a800000802649400 0000000000000000 0000000000000000 [ 34.252996] 0000000000000000 0000400400000000 0000000000000000 1dbd2b22ea1dd500 [ 34.261049] 00000000140000e3 a800000802649400 a800000802649400 a800000808ee0000 [ 34.269103] ... [ 34.271568] Call Trace: [ 34.274026] [<a80000080838e01c>] anon_pipe_read+0xd4/0x428 [ 34.279533] [<a80000080837edf4>] vfs_read+0x25c/0x318 [ 34.284607] [<a80000080837faac>] ksys_read+0x104/0x138 [ 34.289763] [<a80000080802b9cc>] syscall_common+0x44/0x68 [ 34.295187] [ 34.296689] Code: f84000cf 02209825 de020010 <dc420000> d8400004 02002825 0040f809 02802025 f84000c3 [ 34.306504] [ 34.308099] ---[ end trace 0000000000000000 ]---
My initial reproducer was the xdp-tools test suite. A standalone reproducer would be an lld/scd loop that, when the read is reordered by the CPU, triggers a fault. We can achieve this from userspace by stressing an anonymous pipe, which uses a mutex. Program used:
// SPDX-License-Identifier: GPL-2.0
// pipe_race.c - reproducer for MIPS LL/SC reordering vs fs/pipe.c
//
// Two userspace processes on an anonymous pipe:
// parent = writer: tight write() loop
// child = reader: tight read() loop
#define _GNU_SOURCE
#include <assert.h>
#include <errno.h>
#include <sched.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <time.h>
#include <unistd.h>
int main(void)
{
long wrsize = 70; // bytes per write()
long rdsize = 4096; // bytes per read()
int pfd[2];
char *buf;
pid_t pid;
int ret;
ret = pipe(pfd);
assert(!ret);
pid = fork();
assert(pid >= 0);
if (pid == 0) { /* reader */
close(pfd[1]);
buf = malloc(rdsize);
assert(buf);
for (;;) {
ssize_t n = read(pfd[0], buf, rdsize);
if (n < 0 && errno == EINTR)
continue;
if (n <= 0)
_exit(n < 0 ? 1 : 0);
}
}
close(pfd[0]); /* writer */
buf = malloc(wrsize);
assert(buf);
memset(buf, 'x', wrsize);
for (;;) {
ssize_t n = write(pfd[1], buf, wrsize);
if (n < 0 && errno == EINTR)
continue;
if (n != wrsize)
break;
}
kill(pid, SIGKILL);
wait(NULL);
return 0;
}arch/mips/Kconfig +1 -0
@@ -658,6 +658,7 @@ config EYEQ select USB_UHCI_BIG_ENDIAN_MMIO if CPU_BIG_ENDIAN select USE_OF select HOTPLUG_PARALLEL if HOTPLUG_CPU + select WEAK_REORDERING_BEYOND_LLSC help Select this to build a kernel supporting EyeQ SoC from Mobileye.