Folks: I recently uncovered a bug in the block layer. It uses a workqueue to periodically probe removable drives for media or other state changes, and the workqueue it uses is system_nrt_wq.
The bug is that system_nrt_wq is not freezable, so it keeps on running even while the system is in the process of suspending or hibernating. Doing I/O to a suspended drive doesn't work well and in some cases causes nasty problems. Obviously these polls need to stop during a suspend transition. A search through the kernel shows that system_nrt_wq is also used in a few other subsystems: ./fs/cifs/cifssmb.c: queue_work(system_nrt_wq, &rdata->work); ./fs/cifs/cifssmb.c: queue_work(system_nrt_wq, &wdata->work); ./fs/cifs/misc.c: queue_work(system_nrt_wq, ./fs/cifs/connect.c: queue_delayed_work(system_nrt_wq, &server->echo, SMB_ECHO_INTERVAL); ./fs/cifs/connect.c: queue_delayed_work(system_nrt_wq, &tcp_ses->echo, SMB_ECHO_INTERVAL); ./fs/cifs/connect.c: queue_delayed_work(system_nrt_wq, &cifs_sb->prune_tlinks, ./fs/cifs/connect.c: queue_delayed_work(system_nrt_wq, &cifs_sb->prune_tlinks, ./drivers/mmc/core/host.c: queue_work(system_nrt_wq, &host->clk_gate_work); ./drivers/gpu/drm/drm_crtc_helper.c: queue_delayed_work(system_nrt_wq, delayed_work, DRM_OUTPUT_POLL_PERIOD); ./drivers/gpu/drm/drm_crtc_helper.c: queue_delayed_work(system_nrt_wq, &dev->mode_config.output_poll_work, DRM_OUTPUT_POLL_PERIOD); ./drivers/gpu/drm/drm_crtc_helper.c: queue_delayed_work(system_nrt_wq, &dev->mode_config.output_poll_work, 0); ./security/keys/gc.c: queue_work(system_nrt_wq, &key_gc_work); ./security/keys/gc.c: queue_work(system_nrt_wq, &key_gc_work); ./security/keys/gc.c: queue_work(system_nrt_wq, &key_gc_work); ./security/keys/gc.c: queue_work(system_nrt_wq, &key_gc_work); ./security/keys/key.c: queue_work(system_nrt_wq, &key_gc_work); My question to all of you: Should system_nrt_wq be made freezable, or should I create a new workqueue that is both freezable and non-reentrant? And if I do, which of the usages above should be converted to the new workqueue? Thanks, Alan Stern
