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BUG: KCSAN: data-race in shmem_file_read_iter / shmem_setattr

write to 0xffff88810259e760 of 8 bytes by task 19544 on cpu 1:
 i_size_write include/linux/fs.h:870 [inline]
 shmem_setattr+0x2c2/0x590 mm/shmem.c:1108
 notify_change+0x7b3/0xa50 fs/attr.c:336
 do_truncate+0xe0/0x120 fs/open.c:64
 handle_truncate fs/namei.c:2912 [inline]
 do_open fs/namei.c:3258 [inline]
 path_openat+0x1a37/0x20a0 fs/namei.c:3371
 do_filp_open+0xbd/0x1d0 fs/namei.c:3398
 do_sys_openat2+0xa3/0x240 fs/open.c:1172
 do_sys_open fs/open.c:1188 [inline]
 __do_sys_creat fs/open.c:1262 [inline]
 __se_sys_creat fs/open.c:1256 [inline]
 __x64_sys_creat+0x62/0x80 fs/open.c:1256
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88810259e760 of 8 bytes by task 19543 on cpu 0:
 i_size_read include/linux/fs.h:848 [inline]
 shmem_file_read_iter+0x446/0x760 mm/shmem.c:2594
 call_read_iter include/linux/fs.h:1895 [inline]
 generic_file_splice_read+0x22a/0x310 fs/splice.c:311
 do_splice_to fs/splice.c:788 [inline]
 splice_direct_to_actor+0x2aa/0x650 fs/splice.c:867
 do_splice_direct+0xf5/0x170 fs/splice.c:976
 do_sendfile+0x5db/0xca0 fs/read_write.c:1257
 __do_sys_sendfile64 fs/read_write.c:1318 [inline]
 __se_sys_sendfile64 fs/read_write.c:1304 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1304
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 19543 Comm: syz-executor.2 Not tainted 5.11.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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