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BUG: KCSAN: data-race in shmem_getpage_gfp / shmem_setattr

write to 0xffff888027102760 of 8 bytes by task 10258 on cpu 1:
 i_size_write include/linux/fs.h:872 [inline]
 shmem_setattr+0x2d7/0x5b0 mm/shmem.c:1082
 notify_change+0x88f/0xa80 fs/attr.c:398
 do_truncate+0xe8/0x130 fs/open.c:64
 handle_truncate fs/namei.c:3018 [inline]
 do_open fs/namei.c:3369 [inline]
 path_openat+0x1b78/0x21b0 fs/namei.c:3498
 do_filp_open+0xbd/0x1d0 fs/namei.c:3525
 do_sys_openat2+0xa3/0x250 fs/open.c:1187
 do_sys_open fs/open.c:1203 [inline]
 __do_sys_open fs/open.c:1211 [inline]
 __se_sys_open fs/open.c:1207 [inline]
 __x64_sys_open+0xe2/0x110 fs/open.c:1207
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888027102760 of 8 bytes by task 10253 on cpu 0:
 i_size_read include/linux/fs.h:850 [inline]
 shmem_getpage_gfp+0x227/0x1980 mm/shmem.c:1814
 shmem_getpage mm/shmem.c:155 [inline]
 shmem_file_read_iter+0x1b8/0x760 mm/shmem.c:2607
 call_read_iter include/linux/fs.h:1971 [inline]
 new_sync_read fs/read_write.c:415 [inline]
 vfs_read+0x565/0x5d0 fs/read_write.c:496
 ksys_read+0xce/0x180 fs/read_write.c:634
 __do_sys_read fs/read_write.c:644 [inline]
 __se_sys_read fs/read_write.c:642 [inline]
 __x64_sys_read+0x3e/0x50 fs/read_write.c:642
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 10253 Comm: syz-executor.0 Tainted: G        W         5.12.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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