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BUG: KCSAN: data-race in cgroup_procs_write_start / handle_mm_fault

write to 0xffff888106d764e8 of 1 bytes by task 12229 on cpu 1:
 mem_cgroup_exit_user_fault include/linux/memcontrol.h:853 [inline]
 handle_mm_fault+0x5dc/0x1a70 mm/memory.c:4554
 do_user_addr_fault+0x60c/0xc00 arch/x86/mm/fault.c:1390
 handle_page_fault arch/x86/mm/fault.c:1475 [inline]
 exc_page_fault+0x94/0x230 arch/x86/mm/fault.c:1531
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:577

read to 0xffff888106d764e8 of 1 bytes by task 1 on cpu 0:
 cgroup_procs_write_start+0x137/0x270 kernel/cgroup/cgroup.c:2792
 __cgroup1_procs_write+0x5d/0x220 kernel/cgroup/cgroup-v1.c:500
 cgroup1_procs_write+0x26/0x30 kernel/cgroup/cgroup-v1.c:532
 cgroup_file_write+0x173/0x2e0 kernel/cgroup/cgroup.c:3698
 kernfs_fop_write_iter+0x1d3/0x2d0 fs/kernfs/file.c:296
 call_write_iter include/linux/fs.h:1977 [inline]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0x69d/0x770 fs/read_write.c:605
 ksys_write+0xce/0x180 fs/read_write.c:658
 __do_sys_write fs/read_write.c:670 [inline]
 __se_sys_write fs/read_write.c:667 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:667
 do_syscall_64+0x34/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 1 Comm: systemd Not tainted 5.12.0-rc8-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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