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BUG: KCSAN: data-race in shmem_getpage_gfp / shmem_write_end

write to 0xffff8881386e8458 of 8 bytes by task 2802 on cpu 0:
 i_size_write include/linux/fs.h:886 [inline]
 shmem_write_end+0x59/0x380 mm/shmem.c:2534
 generic_perform_write+0x264/0x3f0 mm/filemap.c:3749
 __generic_file_write_iter+0xe3/0x280 mm/filemap.c:3866
 generic_file_write_iter+0x79/0x1c0 mm/filemap.c:3898
 call_write_iter include/linux/fs.h:2187 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x468/0x760 fs/read_write.c:578
 ksys_write+0xe8/0x1a0 fs/read_write.c:631
 __do_sys_write fs/read_write.c:643 [inline]
 __se_sys_write fs/read_write.c:640 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:640
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

read to 0xffff8881386e8458 of 8 bytes by task 2811 on cpu 1:
 i_size_read include/linux/fs.h:864 [inline]
 shmem_getpage_gfp+0x1a3/0x1750 mm/shmem.c:1853
 shmem_getpage mm/shmem.c:150 [inline]
 shmem_file_read_iter+0x161/0x6c0 mm/shmem.c:2591
 do_iter_read+0x492/0x760 fs/read_write.c:790
 vfs_readv fs/read_write.c:910 [inline]
 do_preadv+0x159/0x230 fs/read_write.c:1002
 __do_sys_preadv fs/read_write.c:1052 [inline]
 __se_sys_preadv fs/read_write.c:1047 [inline]
 __x64_sys_preadv+0x54/0x60 fs/read_write.c:1047
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

value changed: 0x0000000000fac000 -> 0x0000000000fb1000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 2811 Comm: syz-executor.3 Not tainted 6.0.0-rc2-syzkaller-00248-ge022620b5d05-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/22/2022
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