[moderation] [ext4?] KCSAN: data-race in page_cache_ra_order / page_cache_sync_ra

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: ccd1cdca5cd4 Merge tag 'nfsd-6.19-1' of git://git.kernel.o..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10cf2f1a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=b319ff1b6a2797ca
dashboard link: https://syzkaller.appspot.com/bug?extid=35fa2368394dfb75c36b
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
CC: [adilger...@dilger.ca linux...@vger.kernel.org linux-...@vger.kernel.org ty...@mit.edu]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/12fc5a9ed91b/disk-ccd1cdca.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b6208e3d3a67/vmlinux-ccd1cdca.xz
kernel image: https://storage.googleapis.com/syzbot-assets/785c07926b9a/bzImage-ccd1cdca.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+35fa23...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in page_cache_ra_order / page_cache_sync_ra

write to 0xffff8881048a0c9c of 4 bytes by task 13425 on cpu 1:
page_cache_sync_ra+0x4fd/0x6a0 mm/readahead.c:-1
filemap_get_pages+0x2d0/0x11c0 mm/filemap.c:2690
filemap_splice_read+0x3a9/0x740 mm/filemap.c:3079
ext4_file_splice_read+0x8f/0xb0 fs/ext4/file.c:158
do_splice_read fs/splice.c:982 [inline]
splice_direct_to_actor+0x26f/0x680 fs/splice.c:1086
do_splice_direct_actor fs/splice.c:1204 [inline]
do_splice_direct+0xda/0x150 fs/splice.c:1230
do_sendfile+0x380/0x650 fs/read_write.c:1370
__do_sys_sendfile64 fs/read_write.c:1431 [inline]
__se_sys_sendfile64 fs/read_write.c:1417 [inline]
__x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1417
x64_sys_call+0x2db1/0x3000 arch/x86/include/generated/asm/syscalls_64.h:41
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xca/0x2b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff8881048a0c9c of 4 bytes by task 13430 on cpu 0:
page_cache_ra_order+0xad/0x220 mm/readahead.c:536
page_cache_sync_ra+0x52d/0x6a0 mm/readahead.c:626
filemap_get_pages+0x2d0/0x11c0 mm/filemap.c:2690
filemap_splice_read+0x3a9/0x740 mm/filemap.c:3079
ext4_file_splice_read+0x8f/0xb0 fs/ext4/file.c:158
do_splice_read fs/splice.c:982 [inline]
splice_direct_to_actor+0x26f/0x680 fs/splice.c:1086
do_splice_direct_actor fs/splice.c:1204 [inline]
do_splice_direct+0xda/0x150 fs/splice.c:1230
do_sendfile+0x380/0x650 fs/read_write.c:1370
__do_sys_sendfile64 fs/read_write.c:1431 [inline]
__se_sys_sendfile64 fs/read_write.c:1417 [inline]
__x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1417
x64_sys_call+0x2db1/0x3000 arch/x86/include/generated/asm/syscalls_64.h:41
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xca/0x2b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000009 -> 0x0000000a

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 13430 Comm: syz.9.3369 Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================


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