On 01/31/14 06:58, James Bottomley wrote: > On Thu, 2014-01-30 at 20:46 +0100, Bart Van Assche wrote: >> On 06/25/13 18:13, Michael Christie wrote: >> Sorry but I'm afraid that making the SCSI core invoke a callback >> function from a device, target or host release function would create a >> new challenge, namely making sure that all these callback functions have >> finished before the module is unloaded that contains the SCSI host >> template and the code implementing such a callback function. That >> challenge is not specific to the SCSI infrastructure but is a general >> question that has not yet been solved in the Linux kernel (see e.g. >> "[PATCH] kobject: provide kobject_put_wait to fix module unload race" >> for a more general discussion about how to ensure that kobject release >> functions are invoked before the module is unloaded that owns the >> release function - http://thread.gmane.org/gmane.linux.kernel/1622885). > > For callbacks, that's easy: it's module_get/module_put Adding a module_get() call in scsi_add_host() and a module_put() call in scsi_host_dev_release() would cause a behavior change that would be reported by end users as "system hangs during shutdown". Today it is possible to unload a kernel module via rmmod that created one or more SCSI hosts. Since user space does not remove SCSI hosts during system shutdown, trying to unload a SCSI LLD kernel module that had created one or more SCSI hosts would cause the module unload to fail because of a non-zero module reference count. >> In case it is not clear why I'm reviving this discussion: now that the >> "improved eh timeout handler" patch is upstream (commit >> e494f6a728394ab0df194342549ee20e6f0752df) there is an additional way in >> which the SCSI core can invoke an EH function concurrently with or after >> scsi_remove_host() has finished, namely from the TMF work queue >> (tmf_work_q). > > But the fundamental guarantee is that the eh thread for the host (the eh > context if you will) has to be dead before the host can be removed and > the module unloaded. The thread doesn't die until all the work is done. Maybe I'm misunderstanding something, but as far as I can see kthread_stop(shost->ehandler) is invoked from scsi_host_dev_release(). That last function is called by the last scsi_host_put(). And LLD's invoke scsi_host_put() after scsi_remove_host(). In other words, the SCSI error handler thread and TMF work queue are still active when scsi_remove_host() returns. Should I repost the patch at the start of this thread ? Thanks, Bart. -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
