[syzbot] [netfs?] KCSAN: data-race in netfs_advance_write / netfs_write_collection_worker

[syzbot <syzbot+912f708269025e337cba@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    d082ecbc71e9 Linux 6.14-rc4
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=130277f8580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e9dd6c7eeba2114e
dashboard link: https://syzkaller.appspot.com/bug?extid=912f708269025e337cba
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/2b352c2abb77/disk-d082ecbc.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/c5f4a062a264/vmlinux-d082ecbc.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c3a86625df5a/bzImage-d082ecbc.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+912f708269025e337cba@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in netfs_advance_write / netfs_write_collection_worker

write to 0xffff8881188765b8 of 8 bytes by task 3523 on cpu 0:
 netfs_prepare_write fs/netfs/write_issue.c:210 [inline]
 netfs_advance_write+0x36f/0x610 fs/netfs/write_issue.c:298
 netfs_unbuffered_write+0xde/0x330 fs/netfs/write_issue.c:721
 netfs_unbuffered_write_iter_locked+0x2b7/0x570 fs/netfs/direct_write.c:100
 netfs_unbuffered_write_iter+0x2b7/0x3b0 fs/netfs/direct_write.c:195
 v9fs_file_write_iter+0x60/0x80 fs/9p/vfs_file.c:404
 new_sync_write fs/read_write.c:586 [inline]
 vfs_write+0x77b/0x920 fs/read_write.c:679
 ksys_write+0xe8/0x1b0 fs/read_write.c:731
 __do_sys_write fs/read_write.c:742 [inline]
 __se_sys_write fs/read_write.c:739 [inline]
 __x64_sys_write+0x42/0x50 fs/read_write.c:739
 x64_sys_call+0x287e/0x2dc0 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff8881188765b8 of 8 bytes by task 50 on cpu 1:
 netfs_collect_write_results fs/netfs/write_collect.c:231 [inline]
 netfs_write_collection_worker+0x3ee/0x2530 fs/netfs/write_collect.c:374
 process_one_work kernel/workqueue.c:3236 [inline]
 process_scheduled_works+0x4db/0xa20 kernel/workqueue.c:3317
 worker_thread+0x51d/0x6f0 kernel/workqueue.c:3398
 kthread+0x4ae/0x520 kernel/kthread.c:464
 ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

value changed: 0x0000000000000000 -> 0xffff888103259900

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 50 Comm: kworker/u8:3 Not tainted 6.14.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Workqueue: events_unbound netfs_write_collection_worker
==================================================================


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