syzbot

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BUG: KCSAN: data-race in shmem_fallocate / shmem_writeout

read-write to 0xffffc900063c7e30 of 8 bytes by task 24596 on cpu 0:
 shmem_writeout+0x2f1/0x920 mm/shmem.c:1670
 writeout mm/vmscan.c:630 [inline]
 pageout mm/vmscan.c:679 [inline]
 shrink_folio_list+0x1f52/0x2840 mm/vmscan.c:1400
 evict_folios+0x285f/0x3370 mm/vmscan.c:4854
 try_to_shrink_lruvec+0x858/0xc20 mm/vmscan.c:5009
 lru_gen_shrink_lruvec mm/vmscan.c:5173 [inline]
 shrink_lruvec+0x256/0x1bc0 mm/vmscan.c:5932
 shrink_node_memcgs mm/vmscan.c:6171 [inline]
 shrink_node+0x697/0x20a0 mm/vmscan.c:6215
 shrink_zones mm/vmscan.c:6454 [inline]
 do_try_to_free_pages+0x408/0xc90 mm/vmscan.c:6516
 try_to_free_mem_cgroup_pages+0x201/0x420 mm/vmscan.c:6838
 try_charge_memcg+0x373/0xa10 mm/memcontrol.c:2618
 obj_cgroup_charge_pages mm/memcontrol.c:3060 [inline]
 __memcg_kmem_charge_page+0x1ce/0x3f0 mm/memcontrol.c:3104
 __alloc_frozen_pages_noprof+0x18a/0x350 mm/page_alloc.c:5243
 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

read to 0xffffc900063c7e30 of 8 bytes by task 24594 on cpu 1:
 shmem_fallocate+0x5c0/0x920 mm/shmem.c:3763
 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

value changed: 0x0000000000000ba6 -> 0x0000000000000bac

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 24594 Comm: syz.6.5963 Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
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