Nicolai Stange <nstange@xxxxxxx> writes: > Bart Van Assche <bvanassche@xxxxxxx> writes: > >> The description of this patch mentions a single blk_release_queue() call >> that happened in the past from a context from which sleeping is not >> allowed and from which sleeping is allowed today. Have all other >> blk_release_queue() / blk_put_queue() calls been verified to see whether >> none of these happens from a context from which sleeping is not allowed? > > I've just done this today and found the following potentially > problematic call paths to blk_put_queue(). > > 1.) mem_cgroup_throttle_swaprate() takes a spinlock and > calls blkcg_schedule_throttle()->blk_put_queue(). > > Also note that AFAICS mem_cgroup_try_charge_delay() can be called > with GFP_ATOMIC. > > 2.) scsi_unblock_requests() gets called from a lot of drivers and > invoke blk_put_queue() through > scsi_unblock_requests() -> scsi_run_host_queues() -> > scsi_starved_list_run() -> blk_put_queue(). > > Most call sites are fine, the ones which are not are: > a.) pmcraid_complete_ioa_reset(). This gets assigned > to struct pmcraid_cmd's ->cmd_done and later invoked > under a spinlock. > > b.) qla82xx_fw_dump() and qla8044_fw_dump(). > These can potentially block w/o this patch already, > because both invoke qla2x00_wait_for_chip_reset(). > > However, they can get called from IRQ context. For example, > qla82xx_intr_handler(), qla82xx_msix_default() and > qla82xx_poll() call qla2x00_async_event(), which calls > ->fw_dump(). > > The aforementioned functions can also reach ->fw_dump() through > qla24xx_process_response_queue()->qlt_handle_abts_recv()->qlt_response_pkt_all_vps() > ->qlt_response_pkt()->qlt_handle_abts_completion()->qlt_chk_unresolv_exchg() > -> ->fw_dump(). > > But I'd consider this a problem with the driver -- either > ->fw_dump() can sleep and must not be called from IRQ context > or they must not invoke qla2x00_wait_for_hba_ready(). > > > (I can share the full analysis, but it's lengthy and contains nothing > interesting except for what is listed above). > > > One final note though: If I'm not mistaken, then the final > blk_put_queue() can in principle block even today, simply by virtue of > the kernfs operations invoked through > kobject_put()->kobject_release()->kobject_cleanup()->kobject_del() > ->sysfs_remove_dir()->kernfs_remove()->mutex_lock()?\ That's wrong, I missed kobject_del() invocation issued from blk_unregister_queue(). Thus, blk_put_queue() in its current implementation won't ever block. Thanks, Nicolai -- SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany (HRB 36809, AG Nürnberg), GF: Felix Imendörffer
