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BUG: KCSAN: data-race in shmem_getattr / shmem_getpage_gfp

write to 0xffff8880bb93d958 of 8 bytes by task 9893 on cpu 1:
 shmem_getpage_gfp+0x4d6/0x1390 mm/shmem.c:1888
 shmem_getpage mm/shmem.c:154 [inline]
 shmem_file_read_iter+0x224/0x720 mm/shmem.c:2564
 call_read_iter include/linux/fs.h:1896 [inline]
 do_iter_readv_writev+0x54b/0x5b0 fs/read_write.c:691
 do_iter_read+0x1fc/0x3d0 fs/read_write.c:933
 vfs_iter_read+0x5c/0x80 fs/read_write.c:947
 lo_read_simple drivers/block/loop.c:351 [inline]
 do_req_filebacked drivers/block/loop.c:625 [inline]
 loop_handle_cmd drivers/block/loop.c:1952 [inline]
 loop_queue_work+0x92c/0x1623 drivers/block/loop.c:1966
 kthread_worker_fn+0x1c3/0x3a0 kernel/kthread.c:671
 loop_kthread_worker_fn+0x50/0x70 drivers/block/loop.c:901
 kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

read to 0xffff8880bb93d958 of 8 bytes by task 9869 on cpu 0:
 shmem_getattr+0x6b/0x180 mm/shmem.c:1004
 vfs_getattr_nosec+0x12e/0x170 fs/stat.c:81
 vfs_getattr+0x54/0x70 fs/stat.c:118
 loop_get_status.part.0+0x253/0x380 drivers/block/loop.c:1395
 loop_get_status+0x76/0xb0 include/linux/string.h:363
 loop_get_status64+0x4f/0xd0 drivers/block/loop.c:1503
 lo_ioctl+0x324/0xc80 drivers/block/loop.c:1624
 __blkdev_driver_ioctl block/ioctl.c:277 [inline]
 blkdev_ioctl+0xbe5/0x1260 block/ioctl.c:582
 block_ioctl+0x95/0xc0 fs/block_dev.c:1983
 vfs_ioctl fs/ioctl.c:47 [inline]
 file_ioctl fs/ioctl.c:545 [inline]
 do_vfs_ioctl+0x84f/0xcf0 fs/ioctl.c:732
 ksys_ioctl+0xbd/0xe0 fs/ioctl.c:749
 __do_sys_ioctl fs/ioctl.c:756 [inline]
 __se_sys_ioctl fs/ioctl.c:754 [inline]
 __x64_sys_ioctl+0x4c/0x60 fs/ioctl.c:754
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 9869 Comm: syz-executor.4 Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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