On Thu, 2024-09-05 at 09:33 +0900, Damien Le Moal wrote: > On 2024/09/05 6:10, Alex Williamson wrote: > > On Wed, 4 Sep 2024 23:24:53 +0300 > > Andy Shevchenko <andy.shevchenko@xxxxxxxxx> wrote: > > > > > Wed, Sep 04, 2024 at 12:07:21PM -0600, Alex Williamson kirjoitti: > > > > On Wed, 04 Sep 2024 15:37:25 +0200 > > > > Philipp Stanner <pstanner@xxxxxxxxxx> wrote: > > > > > On Wed, 2024-09-04 at 17:25 +0900, Damien Le Moal wrote: > > > > > > ... > > > > > > > > If vfio-pci can get rid of pci_intx() alltogether, that might > > > > > be a good > > > > > thing. As far as I understood Andy Shevchenko, pci_intx() is > > > > > outdated. > > > > > There's only a hand full of users anyways. > > > > > > > > What's the alternative? > > > > > > From API perspective the pci_alloc_irq_vectors() & Co should be > > > used. > > > > We can't replace a device level INTx control with a vector > > allocation > > function. > > > > > > vfio-pci has a potentially unique requirement > > > > here, we don't know how to handle the device interrupt, we only > > > > forward > > > > it to the userspace driver. As a level triggered interrupt, > > > > INTx will > > > > continue to assert until that userspace driver handles the > > > > device. > > > > That's obviously unacceptable from a host perspective, so INTx > > > > is > > > > masked at the device via pci_intx() where available, or at the > > > > interrupt controller otherwise. The API with the userspace > > > > driver > > > > requires that driver to unmask the interrupt, again resulting > > > > in a call > > > > to pci_intx() or unmasking the interrupt controller, in order > > > > to receive > > > > further interrupts from the device. Thanks, > > > > > > I briefly read the discussion and if I understand it correctly > > > the problem here > > > is in the flow: when the above mentioned API is being called. > > > Hence it's design > > > (or architectural) level of issue and changing call from foo() to > > > bar() won't > > > magically make problem go away. But I might be mistaken. > > > > Certainly from a vector allocation standpoint we can change to > > whatever > > is preferred, but the direct INTx manipulation functions are a > > different thing entirely and afaik there's nothing else that can > > replace them at a low level, nor can we just get rid of our calls > > to > > pci_intx(). Thanks, > > But can these calls be moved out of the spinlock context ? If not, > then we need > to clarify that pci_intx() can be called from any context, which will > require > changing to a GFP_ATOMIC for the resource allocation, even if the use > case > cannot trigger the allocation. This is needed to ensure the > correctness of the > pci_intx() function use. We could do that I guess. As I keep saying, it's not intended to have pci_intx() allocate _permanently_. This is a temporary situation. pci_intx() should have neither devres nor allocation. > Frankly, I am surprised that the might sleep splat you > got was not already reported before (fuzzying, static analyzers might > eventually > catch that though). It's a super rare situation: * pci_intx() has very few callers * It only allocates if pcim_enable_device() instead of pci_enable_device() ran. * It only allocates when it's called for the FIRST TIME * All of the above is only a problem while you hold a lock > > The other solution would be a version of pci_intx() that has a gfp > flags > argument to allow callers to use the right gfp flags for the call > context. I don't think that's a good idea. As I said, I want to clean up all that in the mid term. As a matter of fact, there is already __pcim_intx() in pci/devres.c as a pure unmanaged pci_intx() as a means to split and then cleanup the APIs. One path towards getting the hybrid behavior out of pci_intx() could be to rename __pcim_intx() to pci_intx_unmanaged() and port everyone who uses pci_enable_device() + pci_intx() to that version. That would be better than to have a third version with a gfp_t argument. P. > > > > > > Alex > > >
