Re: [PATCH 1/4] nvmet: pci-epf: Clear completion queue IRQ flag on delete

[Niklas Cassel <cassel@kernel.org>]

On Fri, May 09, 2025 at 08:13:22AM +0900, Damien Le Moal wrote:
> On 5/8/25 10:07 PM, Niklas Cassel wrote:
> > On Thu, May 08, 2025 at 03:57:42PM +0900, Damien Le Moal wrote:
> >> The function nvmet_pci_epf_delete_cq() unconditionnally calls
> > 
> > s/unconditionnally/unconditionally/
> > 
> > 
> >> nvmet_pci_epf_remove_irq_vector() even for completion queues that do not
> >> have interrupts enabled. Furthermore, for completion queues that do
> >> have IRQ enabled, deleting and re-creating the completion queue leaves
> >> the flag NVMET_PCI_EPF_Q_IRQ_ENABLED set, even if the completion queue
> >> is being re-created with IRQ disabled.
> >>
> >> Fix these issues by calling nvmet_pci_epf_remove_irq_vector() only if
> >> NVMET_PCI_EPF_Q_IRQ_ENABLED is set and make sure to always clear that
> >> flag.
> >>
> >> Fixes: 0faa0fe6f90e ("nvmet: New NVMe PCI endpoint function target driver")
> >> Cc: stable@vger.kernel.org
> >> Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
> >> ---
> >>  drivers/nvme/target/pci-epf.c | 3 ++-
> >>  1 file changed, 2 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/nvme/target/pci-epf.c b/drivers/nvme/target/pci-epf.c
> >> index 7fab7f3d79b7..d5442991f2fb 100644
> >> --- a/drivers/nvme/target/pci-epf.c
> >> +++ b/drivers/nvme/target/pci-epf.c
> >> @@ -1344,7 +1344,8 @@ static u16 nvmet_pci_epf_delete_cq(struct nvmet_ctrl *tctrl, u16 cqid)
> >>  
> >>  	cancel_delayed_work_sync(&cq->work);
> >>  	nvmet_pci_epf_drain_queue(cq);
> >> -	nvmet_pci_epf_remove_irq_vector(ctrl, cq->vector);
> >> +	if (test_and_clear_bit(NVMET_PCI_EPF_Q_IRQ_ENABLED, &cq->flags))
> >> +		nvmet_pci_epf_remove_irq_vector(ctrl, cq->vector);
> > 
> > I agree that we should only call nvmet_pci_epf_remove_irq_vector() if
> > NVMET_PCI_EPF_Q_IRQ_ENABLED is set.
> > 
> > However, it looks a bit weird to explicitly only clear only this flag bit.
> > What about the other flag bits?
> 
> NVMET_PCI_EPF_Q_LIVE is cleared in the same function in the same manner. The
> only other flag is NVMET_PCI_EPF_Q_IRQ_ENABLED, which this patch clears.
> 
> > I would have expected a memset() of flags, or flags = 0; in either
> > .create_cq/.create_sq, or in .delete_cq/.delete_sq.

You patch looks fine, I was just thinking that it would be slightly more robust
to do flags = 0; in e.g. .create_cq/.create_sq, or .delete_cq/.delete_sq.

That way, we remove the possibility of ever introducing a similar bug to what
this patch fixes. (I.e if we ever add a new flag, we will not need to remember
to also add code that explicitly clears the bit for that new flag, since
flags = 0; clears all flags in one go.)


Kind regards,
Niklas