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BUG: KCSAN: data-race in loop_configure / shmem_write_begin

read-write to 0xffff8881399895b0 of 4 bytes by task 15916 on cpu 0:
 mapping_set_gfp_mask include/linux/pagemap.h:290 [inline]
 loop_configure+0x7c3/0xca0 drivers/block/loop.c:1077
 lo_ioctl+0x682/0x12e0
 blkdev_ioctl+0x38e/0x480 block/ioctl.c:615
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl+0xc9/0x140 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

read to 0xffff8881399895b0 of 4 bytes by task 15905 on cpu 1:
 mapping_gfp_mask include/linux/pagemap.h:274 [inline]
 shmem_get_folio mm/shmem.c:2080 [inline]
 shmem_write_begin+0x8a/0x1d0 mm/shmem.c:2573
 generic_perform_write+0x1c3/0x3d0 mm/filemap.c:3923
 __generic_file_write_iter+0xe6/0x290 mm/filemap.c:4051
 generic_file_write_iter+0x7d/0x1c0 mm/filemap.c:4083
 do_iter_write+0x4ae/0x770 fs/read_write.c:860
 vfs_writev+0x1a2/0x310 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

value changed: 0x00100cca -> 0x00100c0a

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 15905 Comm: syz-executor.0 Not tainted 6.4.0-rc1-syzkaller-00011-g1dc3731daf1f #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/14/2023
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netlink: 8 bytes leftover after parsing attributes in process `syz-executor.0'.