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BUG: KCSAN: data-race in shmem_add_to_page_cache / shmem_getattr

write to 0xffff888105eb0f50 of 8 bytes by task 20157 on cpu 1:
 shmem_add_to_page_cache+0x52d/0x650 mm/shmem.c:718
 shmem_getpage_gfp+0xbdc/0x1410 mm/shmem.c:1929
 shmem_getpage mm/shmem.c:155 [inline]
 shmem_file_read_iter+0x1a2/0x5c0 mm/shmem.c:2603
 call_read_iter include/linux/fs.h:2108 [inline]
 do_iter_readv_writev+0x2e8/0x360 fs/read_write.c:738
 do_iter_read+0x109/0x4b0 fs/read_write.c:801
 vfs_iter_read+0x4c/0x70 fs/read_write.c:843
 lo_read_simple drivers/block/loop.c:361 [inline]
 do_req_filebacked drivers/block/loop.c:637 [inline]
 loop_handle_cmd drivers/block/loop.c:2046 [inline]
 loop_queue_work+0xdeb/0x1310 drivers/block/loop.c:2064
 kthread_worker_fn+0x280/0x4d0 kernel/kthread.c:756
 loop_kthread_worker_fn+0x3e/0x50 drivers/block/loop.c:933
 kthread+0x1d0/0x1f0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff888105eb0f50 of 8 bytes by task 20149 on cpu 0:
 shmem_getattr+0x6e/0x250 mm/shmem.c:1043
 vfs_getattr_nosec+0x152/0x2f0 fs/stat.c:105
 vfs_getattr+0x4d/0x60 fs/stat.c:142
 loop_get_status+0x23e/0x310 drivers/block/loop.c:1458
 loop_get_status64 drivers/block/loop.c:1566 [inline]
 lo_ioctl+0x1af/0x11f0 drivers/block/loop.c:1711
 blkdev_ioctl+0x1d0/0x3c0 block/ioctl.c:585
 block_ioctl+0x6d/0x80 fs/block_dev.c:1662
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:1069 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:1055
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:1055
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x00000000000000b5 -> 0x00000000000000b9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 20149 Comm: syz-executor.1 Not tainted 5.13.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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 loop1: p1[EZD] p2 p3 p4
loop1: p2 size 1073741824 extends beyond EOD, truncated
loop1: p3 size 1912633224 extends beyond EOD, truncated