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BUG: KCSAN: data-race in loop_configure / shmem_write_end

write to 0xffff888139a83940 of 8 bytes by task 13164 on cpu 0:
 i_size_write include/linux/fs.h:901 [inline]
 shmem_write_end+0x9a/0x4a0 mm/shmem.c:2598
 generic_perform_write+0x26d/0x410 mm/filemap.c:3934
 __generic_file_write_iter+0xa1/0x120 mm/filemap.c:4018
 generic_file_write_iter+0x7d/0x1c0 mm/filemap.c:4044
 do_iter_write+0x4b4/0x7b0 fs/read_write.c:860
 vfs_writev+0x1a8/0x320 fs/read_write.c:933
 do_pwritev fs/read_write.c:1030 [inline]
 __do_sys_pwritev fs/read_write.c:1077 [inline]
 __se_sys_pwritev fs/read_write.c:1072 [inline]
 __x64_sys_pwritev+0x100/0x1c0 fs/read_write.c:1072
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

read to 0xffff888139a83940 of 8 bytes by task 13176 on cpu 1:
 i_size_read include/linux/fs.h:879 [inline]
 get_size drivers/block/loop.c:147 [inline]
 get_loop_size drivers/block/loop.c:165 [inline]
 loop_configure+0xa8d/0xca0 drivers/block/loop.c:1099
 lo_ioctl+0x682/0x12e0
 blkdev_ioctl+0x375/0x460 block/ioctl.c:621
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl+0xcf/0x140 fs/ioctl.c:856
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

value changed: 0x0000000000314000 -> 0x0000000000317000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 13176 Comm: syz-executor.5 Tainted: G        W          6.5.0-rc2-syzkaller-00338-g295e1388de2d #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2023
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loop7: detected capacity change from 0 to 32767