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BUG: KCSAN: data-race in bd_set_size / do_mpage_readpage

write to 0xffff888120693c08 of 8 bytes by task 23297 on cpu 0:
 i_size_write include/linux/fs.h:876 [inline]
 bd_set_size+0x49/0x70 fs/block_dev.c:1377
 __loop_clr_fd+0x375/0x5b0 drivers/block/loop.c:1254
 loop_clr_fd drivers/block/loop.c:1345 [inline]
 lo_ioctl+0x9d1/0x1190 drivers/block/loop.c:1703
 __blkdev_driver_ioctl block/ioctl.c:224 [inline]
 blkdev_ioctl+0x1cf/0x410 block/ioctl.c:620
 block_ioctl+0x6d/0x80 fs/block_dev.c:1871
 vfs_ioctl fs/ioctl.c:48 [inline]
 __do_sys_ioctl fs/ioctl.c:753 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:739
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:739
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888120693c08 of 8 bytes by task 23280 on cpu 1:
 i_size_read include/linux/fs.h:854 [inline]
 do_mpage_readpage+0x157/0x10c0 fs/mpage.c:191
 mpage_readahead+0x151/0x340 fs/mpage.c:391
 blkdev_readahead+0x18/0x20 fs/block_dev.c:608
 read_pages+0x9c/0x700 mm/readahead.c:130
 page_cache_readahead_unbounded+0x41a/0x470 mm/readahead.c:244
 ondemand_readahead+0x4e4/0x6e0 mm/readahead.c:273
 page_cache_async_readahead+0x1c6/0x1e0 mm/readahead.c:631
 generic_file_buffered_read+0x391/0x1f60 mm/filemap.c:2113
 generic_file_read_iter+0x7d/0x3e0 mm/filemap.c:2405
 blkdev_read_iter+0xb3/0xc0 fs/block_dev.c:1927
 call_read_iter include/linux/fs.h:1876 [inline]
 generic_file_splice_read+0x22b/0x310 fs/splice.c:312
 do_splice_to fs/splice.c:870 [inline]
 splice_direct_to_actor+0x2a8/0x660 fs/splice.c:950
 do_splice_direct+0xf2/0x170 fs/splice.c:1059
 do_sendfile+0x56a/0xba0 fs/read_write.c:1540
 __do_sys_sendfile64 fs/read_write.c:1601 [inline]
 __se_sys_sendfile64 fs/read_write.c:1587 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1587
 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: 1 PID: 23280 Comm: syz-executor.1 Not tainted 5.9.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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