==================================================================
BUG: KCSAN: data-race in shmem_fallocate / shmem_writeout

write to 0xffffc90002a67e20 of 8 bytes by task 27069 on cpu 0:
 shmem_fallocate+0x724/0x920 mm/shmem.c:3815
 vfs_fallocate+0x3b6/0x400 fs/open.c:338
 ksys_fallocate fs/open.c:362 [inline]
 __do_sys_fallocate fs/open.c:367 [inline]
 __se_sys_fallocate fs/open.c:365 [inline]
 __x64_sys_fallocate+0x7a/0xd0 fs/open.c:365
 x64_sys_call+0x298e/0x3020 arch/x86/include/generated/asm/syscalls_64.h:286
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffc90002a67e20 of 8 bytes by task 27072 on cpu 1:
 shmem_writeout+0x2c1/0x920 mm/shmem.c:1669
 writeout mm/vmscan.c:650 [inline]
 pageout mm/vmscan.c:699 [inline]
 shrink_folio_list+0x1eed/0x27e0 mm/vmscan.c:1420
 evict_folios+0x28b0/0x33b0 mm/vmscan.c:4724
 try_to_shrink_lruvec+0x81b/0xbf0 mm/vmscan.c:4885
 lru_gen_shrink_lruvec mm/vmscan.c:5034 [inline]
 shrink_lruvec+0x265/0x1b70 mm/vmscan.c:5793
 shrink_node_memcgs mm/vmscan.c:6032 [inline]
 shrink_node+0x699/0x2100 mm/vmscan.c:6076
 shrink_zones mm/vmscan.c:6315 [inline]
 do_try_to_free_pages+0x408/0xc90 mm/vmscan.c:6377
 try_to_free_mem_cgroup_pages+0x201/0x420 mm/vmscan.c:6699
 try_charge_memcg+0x373/0xa10 mm/memcontrol.c:2439
 obj_cgroup_charge_pages mm/memcontrol.c:2882 [inline]
 __memcg_kmem_charge_page+0x139/0x2b0 mm/memcontrol.c:2926
 __alloc_frozen_pages_noprof+0x18a/0x350 mm/page_alloc.c:5245
 alloc_pages_mpol+0xb3/0x260 mm/mempolicy.c:2490
 alloc_frozen_pages_noprof mm/mempolicy.c:2561 [inline]
 alloc_pages_noprof+0x8f/0x140 mm/mempolicy.c:2581
 vm_area_alloc_pages mm/vmalloc.c:3728 [inline]
 __vmalloc_area_node mm/vmalloc.c:3878 [inline]
 __vmalloc_node_range_noprof+0xaed/0x11c0 mm/vmalloc.c:4064
 __kvmalloc_node_noprof+0x3d4/0x640 mm/slub.c:6856
 futex_hash_allocate+0x190/0x9a0 kernel/futex/core.c:1815
 futex_hash_prctl+0xd8/0xf0 kernel/futex/core.c:1961
 __do_sys_prctl kernel/sys.c:2885 [inline]
 __se_sys_prctl+0x4f4/0x1400 kernel/sys.c:2534
 __x64_sys_prctl+0x67/0x80 kernel/sys.c:2534
 x64_sys_call+0x2533/0x3020 arch/x86/include/generated/asm/syscalls_64.h:158
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000001e43 -> 0x0000000000001e44

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 27072 Comm: syz.5.7475 Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
==================================================================