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BUG: KCSAN: data-race in loop_configure / shmem_write_begin

read-write to 0xffff888148c657c8 of 4 bytes by task 18785 on cpu 0:
 mapping_set_gfp_mask include/linux/pagemap.h:310 [inline]
 loop_configure+0x7c0/0xca0 drivers/block/loop.c:1077
 lo_ioctl+0x682/0x12e0
 blkdev_ioctl+0x375/0x460 block/ioctl.c:630
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:871 [inline]
 __se_sys_ioctl+0xcf/0x140 fs/ioctl.c:857
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:857
 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 0xffff888148c657c8 of 4 bytes by task 18778 on cpu 1:
 mapping_gfp_mask include/linux/pagemap.h:294 [inline]
 shmem_get_folio mm/shmem.c:2144 [inline]
 shmem_write_begin+0x8a/0x210 mm/shmem.c:2688
 generic_perform_write+0x1c9/0x410 mm/filemap.c:3969
 shmem_file_write_iter+0xc8/0xe0 mm/shmem.c:2865
 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

value changed: 0x00100cca -> 0x00100c0a

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 18778 Comm: syz-executor.4 Not tainted 6.6.0-rc5-syzkaller-00055-g1c8b86a3799f #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/06/2023
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