syzbot

loop2: detected capacity change from 0 to 264192
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BUG: KCSAN: data-race in shmem_add_to_page_cache / shmem_getattr

write to 0xffff888103cfe840 of 8 bytes by task 4250 on cpu 1:
 shmem_add_to_page_cache+0x4ae/0x590 mm/shmem.c:743
 shmem_getpage_gfp+0xae9/0x12c0 mm/shmem.c:1902
 shmem_getpage mm/shmem.c:149 [inline]
 shmem_file_read_iter+0x1b2/0x5d0 mm/shmem.c:2526
 call_read_iter include/linux/fs.h:2068 [inline]
 do_iter_readv_writev+0x2fb/0x380 fs/read_write.c:723
 do_iter_read+0x192/0x5d0 fs/read_write.c:786
 vfs_iter_read+0x4c/0x70 fs/read_write.c:828
 lo_read_simple drivers/block/loop.c:285 [inline]
 do_req_filebacked drivers/block/loop.c:500 [inline]
 loop_handle_cmd drivers/block/loop.c:1852 [inline]
 loop_process_work+0x746/0x12d0 drivers/block/loop.c:1892
 loop_rootcg_workfn+0x1b/0x20 drivers/block/loop.c:1923
 process_one_work+0x3f6/0x960 kernel/workqueue.c:2307
 worker_thread+0x616/0xa70 kernel/workqueue.c:2454
 kthread+0x1bf/0x1e0 kernel/kthread.c:377
 ret_from_fork+0x1f/0x30

read to 0xffff888103cfe840 of 8 bytes by task 12787 on cpu 0:
 shmem_getattr+0x70/0x240 mm/shmem.c:1054
 vfs_getattr_nosec fs/stat.c:123 [inline]
 vfs_getattr+0x16a/0x1a0 fs/stat.c:160
 loop_get_status+0x162/0x240 drivers/block/loop.c:1336
 loop_get_status64 drivers/block/loop.c:1428 [inline]
 lo_ioctl+0x1eb/0x1260 drivers/block/loop.c:1573
 blkdev_ioctl+0x20e/0x440 block/ioctl.c:588
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:874 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:860
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:860
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x0000000000000000 -> 0x0000000000000001

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 12787 Comm: syz-executor.2 Not tainted 5.17.0-rc7-syzkaller-00235-gaad611a868d1-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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