On 04/05/2012 11:29 PM, Mike Christie wrote: > On 04/05/2012 01:00 PM, Bart Van Assche wrote: >> On 04/05/12 13:58, Tomas Henzl wrote: >> >>> When a rmmod is tried then in some cases the kernel is not able to handle a paging request: >>> [ 727.154296] BUG: unable to handle kernel paging request at ffffffffa01874b8 >>> From what I observerved it happens when when we call the rmmod only a while after a modprobe >>> (in this case it is the mpt2sas driver). More accurately said, it happens when rmmod is called >>> while scsi async is still at work. The driver is removed but the scsi_host_template is still filled >>> with now invalid pointers, in this case it is most likely the hostt->scan_finished which causes the BUG. >> >> Are you sure the above analysis is correct ? I've triggered several >> million device removal events with ib_srp but I haven't ever seen the >> above crash. > ib_srp uses scsi_scan_target when the target is added so you are going > down a different code path. If you are rmmoding ib_srp while the driver > is calling scsi_scan_target() that would be a similar problem. If the driver doesn't define the 'scsi_host_template.scan_finished' then the problem is less visible. It's because in do_scsi_scan_host another path is taken and the scsi_host_scan_allowed test is used to skip further scanning, which I think reduces the risk significantly. ib_srp doesn't define scan_finished so it is not safe but it is less likely it will hit this. > > Tomas's bug occurs when drivers use scsi_scan_host, use the async scsi > device scanning, and then rmmod the LLD while the scan is still in progress. > > I think a general problem that we might hit similar to Tomas's issue is > when scanning from userspace then rmmoding the driver. Maybe that means > we need a more generic fix? Or, maybe that could be handled by having > scsi_scan() do a try_module_get before scanning. I like this idea(try_module_get) it is easy/elegant and it is used in scsi_rescan_device, but a scan can take a lot of time and during that time the driver couldn't be removed. When a flag in scsi_remove_host is set then the scan can be cancelled, if the user rmmods the driver. > -- > 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 -- 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
