On Mon, 26 Jan 2015, Christoph Hellwig wrote: > On Thu, Jan 15, 2015 at 02:40:31PM -0500, Tejun Heo wrote: > > > 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. > > Btw, where do we do that? I did a walk through the code starting > from device_del, but must have missed the obvious. It happens in fs/kernfs/dir.c:kernfs_drain(). That routine is called when a sysfs file is removed, and it waits until all ongoing read/write operations are finished. > > > 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. :) > > No problem. That's the basic situation we are talking about. I have > a serie fixing some long standing issues in the device model integration > in SCSI, and pointed out a possible issue in that area. > > So what is the proper lock to take to prevent ->remove from beeing > called while in such a method? A mentioned about I tried to peel > through all the layers of the onion^H^H^H^H^Hdriver core, but so far > couldn't find anything obvious. The proper lock is dev->mutex, as I mentioned in an earlier email (http://marc.info/?l=linux-scsi&m=142176669519982&w=2). That lock is held whenever a ->remove method is called. Alan Stern -- 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
