[moderation] [fs?] [mm?] KCSAN: data-race in __wb_writeout_add / writeout_period (6)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: dc59e4fea9d8 Linux 7.2-rc1
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14c20832580000
kernel config: https://syzkaller.appspot.com/x/.config?x=84b3039e8461eef5
dashboard link: https://syzkaller.appspot.com/bug?extid=44d48263a5bd8600f264
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
CC: [ak...@linux-foundation.org ja...@suse.cz linux-...@vger.kernel.org linux-...@vger.kernel.org linu...@kvack.org wi...@infradead.org]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c30fa6298c88/disk-dc59e4fe.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/d723159b1484/vmlinux-dc59e4fe.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c0487b8aa33d/bzImage-dc59e4fe.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+44d482...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __wb_writeout_add / writeout_period

write to 0xffffffff893e71f0 of 8 bytes by interrupt on cpu 0:
writeout_period+0xa1/0xe0 mm/page-writeback.c:608
call_timer_fn+0x3b/0x240 kernel/time/timer.c:1748
expire_timers kernel/time/timer.c:1799 [inline]
__run_timers kernel/time/timer.c:2374 [inline]
__run_timer_base+0x40c/0x5f0 kernel/time/timer.c:2386
run_timer_base kernel/time/timer.c:2395 [inline]
run_timer_softirq+0x45/0x70 kernel/time/timer.c:2406
handle_softirqs+0xb9/0x280 kernel/softirq.c:622
__do_softirq kernel/softirq.c:656 [inline]
invoke_softirq kernel/softirq.c:496 [inline]
__irq_exit_rcu+0x42/0xd0 kernel/softirq.c:735
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1062 [inline]
sysvec_apic_timer_interrupt+0x74/0x80 arch/x86/kernel/apic/apic.c:1062
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:674
console_flush_one_record arch/x86/include/asm/irqflags.h:-1 [inline]
console_flush_all+0x513/0x6b0 kernel/printk/printk.c:3343
__console_flush_and_unlock kernel/printk/printk.c:3373 [inline]
console_unlock+0xa1/0x280 kernel/printk/printk.c:3413
vprintk_emit+0x3e4/0x600 kernel/printk/printk.c:2479
vprintk_default+0x26/0x30 kernel/printk/printk.c:2494
vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
_printk+0x79/0xa0 kernel/printk/printk.c:2504
bio_check_eod block/blk-core.c:609 [inline]
submit_bio_noacct+0x85f/0x920 block/blk-core.c:843
submit_bio+0x2a4/0x2c0 block/blk-core.c:962
mpage_bio_submit_write fs/mpage.c:82 [inline]
mpage_write_folio fs/mpage.c:593 [inline]
__mpage_writepages+0x946/0x1370 fs/mpage.c:686
mpage_writepages include/linux/mpage.h:27 [inline]
fat_writepages+0x26/0x30 fs/fat/inode.c:200
do_writepages+0x1b9/0x300 mm/page-writeback.c:2571
filemap_writeback mm/filemap.c:387 [inline]
filemap_fdatawrite_range mm/filemap.c:412 [inline]
filemap_fdatawrite+0x100/0x140 mm/filemap.c:418
writeback_inode fs/fat/inode.c:1888 [inline]
fat_flush_inodes+0xcc/0x150 fs/fat/inode.c:1906
fat_truncate_blocks+0x536/0x5b0 fs/fat/file.c:399
fat_write_failed fs/fat/inode.c:219 [inline]
fat_write_begin+0xc0/0xe0 fs/fat/inode.c:234
generic_perform_write+0x186/0x490 mm/filemap.c:4358
__generic_file_write_iter+0x9e/0x120 mm/filemap.c:4475
generic_file_write_iter+0x77/0x1f0 mm/filemap.c:4501
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x57d/0x990 fs/read_write.c:687
ksys_write+0xdc/0x1a0 fs/read_write.c:739
__do_sys_write fs/read_write.c:750 [inline]
__se_sys_write fs/read_write.c:747 [inline]
__x64_sys_write+0x40/0x50 fs/read_write.c:747
x64_sys_call+0x27e1/0x3020 arch/x86/include/generated/asm/syscalls_64.h:2
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff893e71f0 of 8 bytes by task 40 on cpu 1:
wb_domain_writeout_add mm/page-writeback.c:557 [inline]
__wb_writeout_add+0x81/0x1b0 mm/page-writeback.c:578
__folio_end_writeback+0x14b/0x360 mm/page-writeback.c:2976
folio_end_writeback_no_dropbehind+0x6d/0x1d0 mm/filemap.c:1666
folio_end_writeback+0x1c/0x70 mm/filemap.c:1692
ext4_finish_bio+0x454/0x770 fs/ext4/page-io.c:144
ext4_release_io_end+0x9f/0x1f0 fs/ext4/page-io.c:159
ext4_end_io_end+0x18d/0x240 fs/ext4/page-io.c:210
ext4_do_flush_completed_IO fs/ext4/page-io.c:290 [inline]
ext4_end_io_rsv_work+0x15b/0x1f0 fs/ext4/page-io.c:305
process_one_work kernel/workqueue.c:3322 [inline]
process_scheduled_works+0x4d4/0x9a0 kernel/workqueue.c:3405
worker_thread+0x569/0x750 kernel/workqueue.c:3486
kthread+0x221/0x270 kernel/kthread.c:436
ret_from_fork+0x146/0x330 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

value changed: 0x00000000ffffa020 -> 0x00000000ffffa14c

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 40 Comm: kworker/u8:2 Not tainted syzkaller #0 PREEMPT(lazy)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Workqueue: ext4-rsv-conversion ext4_end_io_rsv_work
==================================================================


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