==================================================================
BUG: KCSAN: data-race in __fat_write_inode / copy_folio_from_iter_atomic
write to 0xffff88810acb307c of 4 bytes by task 7869 on cpu 0:
__fat_write_inode+0x236/0x520 fs/fat/inode.c:-1
fat_write_inode+0xbf/0xd0 fs/fat/inode.c:925
write_inode fs/fs-writeback.c:1582 [inline]
__writeback_single_inode+0x324/0x7c0 fs/fs-writeback.c:1802
writeback_single_inode+0x16d/0x3f0 fs/fs-writeback.c:1858
sync_inode_metadata+0x5b/0x90 fs/fs-writeback.c:2944
writeback_inode fs/fat/inode.c:1875 [inline]
fat_flush_inodes+0x77/0x150 fs/fat/inode.c:1895
fat_truncate_blocks+0x4d8/0x550 fs/fat/file.c:395
fat_write_failed fs/fat/inode.c:219 [inline]
fat_write_end+0xba/0x160 fs/fat/inode.c:247
generic_perform_write+0x312/0x490 mm/filemap.c:4335
__generic_file_write_iter+0xec/0x120 mm/filemap.c:4428
generic_file_write_iter+0x8d/0x2f0 mm/filemap.c:4457
new_sync_write fs/read_write.c:593 [inline]
vfs_write+0x52a/0x960 fs/read_write.c:686
ksys_write+0xda/0x1a0 fs/read_write.c:738
__do_sys_write fs/read_write.c:749 [inline]
__se_sys_write fs/read_write.c:746 [inline]
__x64_sys_write+0x40/0x50 fs/read_write.c:746
x64_sys_call+0x2847/0x3000 arch/x86/include/generated/asm/syscalls_64.h:2
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd8/0x2a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
read to 0xffff88810acb3000 of 2048 bytes by task 27342 on cpu 1:
memcpy_from_iter lib/iov_iter.c:85 [inline]
iterate_bvec include/linux/iov_iter.h:123 [inline]
iterate_and_advance2 include/linux/iov_iter.h:306 [inline]
iterate_and_advance include/linux/iov_iter.h:330 [inline]
__copy_from_iter lib/iov_iter.c:261 [inline]
copy_folio_from_iter_atomic+0x760/0x1150 lib/iov_iter.c:491
generic_perform_write+0x2c2/0x490 mm/filemap.c:4332
shmem_file_write_iter+0xc5/0xf0 mm/shmem.c:3490
lo_rw_aio+0x673/0x720 drivers/block/loop.c:-1
do_req_filebacked drivers/block/loop.c:-1 [inline]
loop_handle_cmd drivers/block/loop.c:1926 [inline]
loop_process_work+0x56d/0xaa0 drivers/block/loop.c:1961
loop_workfn+0x31/0x40 drivers/block/loop.c:1985
process_one_work kernel/workqueue.c:3257 [inline]
process_scheduled_works+0x4ce/0x9d0 kernel/workqueue.c:3340
worker_thread+0x582/0x770 kernel/workqueue.c:3421
kthread+0x489/0x510 kernel/kthread.c:463
ret_from_fork+0x149/0x290 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 27342 Comm: kworker/u8:21 Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: loop2 loop_workfn
==================================================================
bond0: (slave netdevsim1): Releasing backup interface
bridge_slave_1: left allmulticast mode
bridge_slave_1: left promiscuous mode
bridge0: port 2(bridge_slave_1) entered disabled state
bridge_slave_0: left allmulticast mode
bridge_slave_0: left promiscuous mode
bridge0: port 1(bridge_slave_0) entered disabled state
bond0 (unregistering): (slave bond_slave_0): Releasing backup interface
bond0 (unregistering): (slave bond_slave_1): Releasing backup interface
bond0 (unregistering): Released all slaves
bond1 (unregistering): Released all slaves
bond2 (unregistering): Released all slaves
bond3 (unregistering): Released all slaves
bond4 (unregistering): Released all slaves
hsr_slave_0: left promiscuous mode
hsr_slave_1: left promiscuous mode
batman_adv: batadv0: Removing interface: batadv_slave_0
batman_adv: batadv0: Removing interface: batadv_slave_1
IPVS: stop unused estimator thread 0...
netdevsim netdevsim2 netdevsim3 (unregistering): unset [1, 0] type 2 family 0 port 50037 - 0
netdevsim netdevsim2 netdevsim3 (unregistering): unset [1, 1] type 2 family 0 port 20002 - 0
netdevsim netdevsim2 netdevsim2 (unregistering): unset [1, 0] type 2 family 0 port 50037 - 0
netdevsim netdevsim2 netdevsim2 (unregistering): unset [1, 1] type 2 family 0 port 20002 - 0
netdevsim netdevsim2 netdevsim1 (unregistering): unset [1, 0] type 2 family 0 port 50037 - 0
netdevsim netdevsim2 netdevsim1 (unregistering): unset [1, 1] type 2 family 0 port 20002 - 0
netdevsim netdevsim2 (unregistering): unset [1, 0] type 2 family 0 port 50037 - 0
netdevsim netdevsim2 (unregistering): unset [1, 1] type 2 family 0 port 20002 - 0
O3c: left allmulticast mode
O3c: left promiscuous mode
bridge0: port 1(O3c) entered disabled state
bond0 (unregistering): Released all slaves
bond1 (unregistering): Released all slaves
bond2 (unregistering): Released all slaves
bond3 (unregistering): Released all slaves
bond4 (unregistering): Released all slaves
bond5 (unregistering): Released all slaves
bond6 (unregistering): Released all slaves
bond7 (unregistering): Released all slaves
$H (unregistering): (slave bond_slave_0): Releasing backup interface
bond_slave_0: left promiscuous mode
$H (unregistering): (slave bond_slave_1): Releasing backup interface
bond_slave_1: left promiscuous mode
$H (unregistering): Released all slaves
bond1 (unregistering): Released all slaves
bond2 (unregistering): Released all slaves
bond0 (unregistering): Released all slaves
bond3 (unregistering): Released all slaves
bond1 (unregistering): Released all slaves
bond2 (unregistering): Released all slaves
bond0 (unregistering): Released all slaves
bond3 (unregistering): Released all slaves
bond4 (unregistering): Released all slaves
bond5 (unregistering): Released all slaves
tipc: Disabling bearer <udp:syz0>
tipc: Left network mode
hsr_slave_0: left promiscuous mode
hsr_slave_1: left promiscuous mode
batman_adv: batadv0: Removing interface: batadv_slave_1
batman_adv: batadv0: Removing interface: batadv_slave_0
batman_adv: batadv0: Removing interface: batadv_slave_1
hsr_slave_0: left promiscuous mode
hsr_slave_1: left promiscuous mode
batman_adv: batadv0: Removing interface: batadv_slave_0
batman_adv: batadv0: Removing interface: batadv_slave_1
batman_adv: batadv0: Interface deactivated: veth1_vlan
batman_adv: batadv0: Removing interface: veth1_vlan
team0 (unregistering): Port device team_slave_1 removed
team0 (unregistering): Port device team_slave_0 removed
team0 (unregistering): Port device team_slave_1 removed
team0 (unregistering): Port device team_slave_0 removed
team0 (unregistering): Port device team_slave_1 removed
team0 (unregistering): Port device team_slave_0 removed
IPVS: stop unused estimator thread 0...
IPVS: stop unused estimator thread 0...