On Thu, Feb 02, 2023 at 06:56:12PM +0800, Qi Zheng wrote: > The debugfs_remove_recursive() is invoked by unregister_shrinker(), > which is holding the write lock of shrinker_rwsem. It will waits > for the handler of debugfs file complete. The handler also needs > to hold the read lock of shrinker_rwsem to do something. So it > may cause the following deadlock: > > CPU0 CPU1 > > debugfs_file_get() > shrinker_debugfs_count_show()/shrinker_debugfs_scan_write() > > unregister_shrinker() > --> down_write(&shrinker_rwsem); > debugfs_remove_recursive() > // wait for (A) > --> wait_for_completion(); > > // wait for (B) > --> down_read_killable(&shrinker_rwsem) > debugfs_file_put() -- (A) > > up_write() -- (B) > > The down_read_killable() can be killed, so that the above deadlock > can be recovered. But it still requires an extra kill action, > otherwise it will block all subsequent shrinker-related operations, > so it's better to fix it. Oh, indeed, great catch! With Andrew's fixup: Reviewed-by: Roman Gushchin <roman.gushchin@xxxxxxxxx> Thank you!
