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BUG: KCSAN: data-race in shmem_fallocate / shmem_writeout

read-write to 0xffffc90006d6bcc0 of 8 bytes by task 18280 on cpu 0:
 shmem_writeout+0x2eb/0x8f0 mm/shmem.c:1678
 pageout mm/vmscan.c:655 [inline]
 shrink_folio_list+0x1ebb/0x2780 mm/vmscan.c:1397
 evict_folios+0x20e2/0x2d60 mm/vmscan.c:4834
 try_to_shrink_lruvec+0x7c5/0xb10 mm/vmscan.c:4980
 lru_gen_shrink_lruvec mm/vmscan.c:5125 [inline]
 shrink_lruvec+0x25e/0x1b60 mm/vmscan.c:5885
 shrink_node_memcgs mm/vmscan.c:6124 [inline]
 shrink_node+0x69d/0x20f0 mm/vmscan.c:6168
 shrink_zones mm/vmscan.c:6407 [inline]
 do_try_to_free_pages+0x408/0xc90 mm/vmscan.c:6469
 try_to_free_mem_cgroup_pages+0x201/0x420 mm/vmscan.c:6791
 mem_cgroup_resize_max+0x1cd/0x240 mm/memcontrol-v1.c:1522
 mem_cgroup_write+0x1ad/0x250 mm/memcontrol-v1.c:-1
 cgroup_file_write+0x197/0x350 kernel/cgroup/cgroup.c:4316
 kernfs_fop_write_iter+0x1d2/0x2e0 fs/kernfs/file.c:345
 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 0xffffc90006d6bcc0 of 8 bytes by task 18275 on cpu 1:
 shmem_fallocate+0x589/0x8f0 mm/shmem.c:3709
 vfs_fallocate+0x3ac/0x400 fs/open.c:338
 ioctl_preallocate fs/ioctl.c:289 [inline]
 file_ioctl+0x4e1/0x5b0 fs/ioctl.c:-1
 do_vfs_ioctl+0x7c4/0xe50 fs/ioctl.c:576
 __do_sys_ioctl fs/ioctl.c:595 [inline]
 __se_sys_ioctl+0x82/0x140 fs/ioctl.c:583
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:583
 x64_sys_call+0x1563/0x3020 arch/x86/include/generated/asm/syscalls_64.h:17
 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

value changed: 0x00000000000003ad -> 0x00000000000003b8

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 18275 Comm: syz.1.6359 Tainted: G        W           syzkaller #0 PREEMPT(lazy) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
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