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BUG: KCSAN: data-race in do_preadv / proc_tgid_io_accounting

write to 0xffff88812e7e7880 of 8 bytes by task 7056 on cpu 1:
 add_rchar include/linux/sched/xacct.h:14 [inline]
 do_preadv+0x1b5/0x230 fs/read_write.c:1018
 __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_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88812e7e7880 of 8 bytes by task 7086 on cpu 0:
 task_chr_io_accounting_add include/linux/task_io_accounting_ops.h:96 [inline]
 task_io_accounting_add include/linux/task_io_accounting_ops.h:111 [inline]
 do_io_accounting fs/proc/base.c:2959 [inline]
 proc_tgid_io_accounting+0x23c/0x3e0 fs/proc/base.c:2994
 proc_single_show+0x84/0x100 fs/proc/base.c:774
 seq_read_iter+0x2e1/0x930 fs/seq_file.c:230
 seq_read+0x221/0x260 fs/seq_file.c:162
 vfs_read+0x154/0x5d0 fs/read_write.c:494
 ksys_pread64 fs/read_write.c:686 [inline]
 __do_sys_pread64 fs/read_write.c:696 [inline]
 __se_sys_pread64 fs/read_write.c:693 [inline]
 __x64_sys_pread64+0xf5/0x150 fs/read_write.c:693
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x00000000000000ce -> 0x00000000000000f3

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 7086 Comm: syz-executor.3 Tainted: G        W         5.14.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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