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BUG: KCSAN: data-race in __kernel_write / proc_tgid_io_accounting

write to 0xffff88812c1298a0 of 8 bytes by task 4198 on cpu 0:
 inc_syscw include/linux/sched/xacct.h:29 [inline]
 __kernel_write+0x4a3/0x580 fs/read_write.c:557
 do_acct_process+0xaf7/0xc90 kernel/acct.c:519
 slow_acct_process kernel/acct.c:578 [inline]
 acct_process+0x1ed/0x260 kernel/acct.c:602
 do_exit+0x409/0x1560 kernel/exit.c:816
 __do_sys_exit+0xb/0x10 kernel/exit.c:892
 __se_sys_exit+0x5/0x10 kernel/exit.c:890
 __x64_sys_exit+0x16/0x20 kernel/exit.c:890
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88812c1298a0 of 8 bytes by task 4197 on cpu 1:
 do_io_accounting fs/proc/base.c:2928 [inline]
 proc_tgid_io_accounting+0x7d/0x3e0 fs/proc/base.c:2981
 proc_single_show+0x84/0x100 fs/proc/base.c:774
 traverse+0x145/0x380 fs/seq_file.c:108
 seq_read_iter+0x859/0x910 fs/seq_file.c:192
 seq_read+0x221/0x260 fs/seq_file.c:159
 do_loop_readv_writev fs/read_write.c:761 [inline]
 do_iter_read+0x2be/0x4b0 fs/read_write.c:803
 vfs_readv fs/read_write.c:921 [inline]
 do_preadv+0x13b/0x230 fs/read_write.c:1013
 __do_sys_preadv fs/read_write.c:1063 [inline]
 __se_sys_preadv fs/read_write.c:1058 [inline]
 __x64_sys_preadv+0x54/0x60 fs/read_write.c:1058
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 4197 Comm: syz-executor.2 Tainted: G        W         5.12.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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