On Tue, 30 May 2017 16:34:29 -0700, Jakub Kicinski wrote: > On Tue, 30 May 2017 18:07:18 -0500, Bjorn Helgaas wrote: > > On Fri, May 26, 2017 at 04:58:20PM -0700, Jakub Kicinski wrote: > > > On Fri, 26 May 2017 18:47:26 -0500, Bjorn Helgaas wrote: > > > > On Mon, May 22, 2017 at 03:50:23PM -0700, Jakub Kicinski wrote: > > > > > PCI core sets the driver pointer before calling ->probe() and only > > > > > clears it after ->remove(). This means driver's ->sriov_configure() > > > > > callback will happily race with probe() and remove(), most likely > > > > > leading to BUGs, since drivers don't expect this. > > > > > > > > I guess you're referring to the pci_dev->driver pointer set by > > > > local_pci_probe(), and this is important because sriov_numvfs_store() > > > > checks that pointer, right? > > > > > > Yes, exactly. I initially thought this is how the safety of sriov > > > callback may have been ensured, but since the order of > > > local_pci_probe() and the assignment is what it is, it can't. > > > > Right. I was hoping other subsystems would establish a convention > > about whether we set the ->driver pointer before or after calling the > > driver probe() method, but if there is one, I don't see it. > > local_pci_probe() and really_probe() set ->driver first, but > > pnp_device_probe() calls the probe() method first. > > I didn't dig into reordering the pointer setting, to be honest. I > thought establishing that driver callbacks should generally hold device > lock, whenever possible, would be even better than pointer setting > conventions. > > If we order the assignments better, wouldn't we still need appropriate > memory barriers to rely on the order? (: > > > Can you expand on how you reproduce this problem? The only real way I > > see to call ->sriov_configure() is via the sysfs entry point, and I > > would think user-space code would typically not touch that until after > > it knows the driver has claimed a device. But I can certainly imagine > > targeted test code that could hit this problem. > > Correct. It's not something that users should be triggering often in > normal use. I also found it by code inspection rather than by getting > an oops. > > OTOH if the driver performs FW load or other time-consuming operations > in ->probe() the time window when this can be triggered may be counted > in seconds. Hi Bjorn, is this patch still considered for 4.13, or should I change it somehow?
