Hello, Alan. On Thu, Jan 15, 2015 at 01:22:03PM -0500, Alan Stern wrote: > > It has a reference to keep it from beeing freed, but so far I can't find > > anything that prevents ->remove from beeing called while we are in or > > just before a method call. > > There are two types of methods to think about: Those registered by the > subsystem and those registered by the driver. > > If a method is registered by the driver, then the driver will > unregister it when the ->remove routine runs. I don't know for > certain, but I would expect that the sysfs/kernfs core will make sure > that any existing method calls complete before unregister returns. > This would prevent races. Yes, attribute deletions are blocked till the on-going sysfs read/write operations are finished and further rw accesses are failed. > If a method is registered by the subsystem, and if the method runs > entirely within the subsystem's code, then ->remove doesn't matter. > The driver could be unbound while the method is running and it would be > okay. > > The only time we have a problem is when the method is registered by the > subsystem and the method calls into the driver. (Note that this is > exactly what happens with scsi_rescan_device.) > > > > > But this seems like a more generic problem, and at least a quick glance at > > > > the pci_driver methods seems like others don't have a good > > > > synchroniation of ->remove against random driver methods. > > > > > > Can you give one or two examples? > > > > I look at the sriov_configure PCI method, or the various sub-methods > > under pci_driver.err_handler. > > The sriov_numvfs_store method does have the same problem, and so does > the reset_store method (by way of pci_reset_function -> > pci_dev_save_and_disable -> pci_reset_notify). > > Tejun, is my analysis correct? How should we fix these races? I'm not really following what the actual problem case is, so SCSI subsystem store methods are derefing dev->driver without synchronizing against detach events? If that's the case, the solution would be synchronizing against attach/detach events? Sorry if I'm being totally idiotic. I'm having a bit of hard time jumping right in. :) Thanks. -- tejun -- 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
