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BUG: KCSAN: data-race in shmem_getpage_gfp / shmem_setattr

write to 0xffff888135170390 of 8 bytes by task 13577 on cpu 1:
 i_size_write include/linux/fs.h:870 [inline]
 shmem_setattr+0x2c2/0x590 mm/shmem.c:1108
 notify_change+0x86d/0xa60 fs/attr.c:336
 do_truncate fs/open.c:64 [inline]
 do_sys_ftruncate+0x42d/0x530 fs/open.c:195
 __do_sys_ftruncate fs/open.c:205 [inline]
 __se_sys_ftruncate fs/open.c:203 [inline]
 __x64_sys_ftruncate+0x2f/0x40 fs/open.c:203
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888135170390 of 8 bytes by task 13575 on cpu 0:
 i_size_read include/linux/fs.h:848 [inline]
 shmem_getpage_gfp+0x204/0x1930 mm/shmem.c:1815
 shmem_getpage mm/shmem.c:155 [inline]
 shmem_file_read_iter+0x1b8/0x760 mm/shmem.c:2605
 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+0x5e0/0xcf0 fs/read_write.c:1257
 __do_sys_sendfile64 fs/read_write.c:1312 [inline]
 __se_sys_sendfile64 fs/read_write.c:1304 [inline]
 __x64_sys_sendfile64+0xa9/0x130 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: 13575 Comm: syz-executor.5 Not tainted 5.11.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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