Re: [PATCH v2] PCI: Fix potential deadlock in pcim_intx()

[Bjorn Helgaas]

On Thu, Sep 05, 2024 at 09:25:57AM +0200, Philipp Stanner wrote:
> commit 25216afc9db5 ("PCI: Add managed pcim_intx()") moved the
> allocation step for pci_intx()'s device resource from
> pcim_enable_device() to pcim_intx(). As before, pcim_enable_device()
> sets pci_dev.is_managed to true; and it is never set to false again.
> 
> Due to the lifecycle of a struct pci_dev, it can happen that a second
> driver obtains the same pci_dev after a first driver ran.
> If one driver uses pcim_enable_device() and the other doesn't,
> this causes the other driver to run into managed pcim_intx(), which will
> try to allocate when called for the first time.
> 
> Allocations might sleep, so calling pci_intx() while holding spinlocks
> becomes then invalid, which causes lockdep warnings and could cause
> deadlocks:
> 
> ========================================================
> WARNING: possible irq lock inversion dependency detected
> 6.11.0-rc6+ #59 Tainted: G        W
> --------------------------------------------------------
> CPU 0/KVM/1537 just changed the state of lock:
> ffffa0f0cff965f0 (&vdev->irqlock){-...}-{2:2}, at:
> vfio_intx_handler+0x21/0xd0 [vfio_pci_core] but this lock took another,
> HARDIRQ-unsafe lock in the past: (fs_reclaim){+.+.}-{0:0}
> 
> and interrupts could create inverse lock ordering between them.
> 
> other info that might help us debug this:
>  Possible interrupt unsafe locking scenario:
> 
>        CPU0                    CPU1
>        ----                    ----
>   lock(fs_reclaim);
>                                local_irq_disable();
>                                lock(&vdev->irqlock);
>                                lock(fs_reclaim);
>   <Interrupt>
>     lock(&vdev->irqlock);
> 
>  *** DEADLOCK ***
> 
> Have pcim_enable_device()'s release function, pcim_disable_device(), set
> pci_dev.is_managed to false so that subsequent drivers using the same
> struct pci_dev do implicitly run into managed code.
> 
> Fixes: 25216afc9db5 ("PCI: Add managed pcim_intx()")
> Reported-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> Closes: https://lore.kernel.org/all/20240903094431.63551744.alex.williamson@xxxxxxxxxx/
> Suggested-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> Signed-off-by: Philipp Stanner <pstanner@xxxxxxxxxx>
> Tested-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> ---
> @Bjorn:
> This problem was introduced in the v6.11 merge window. So one might
> consider getting it into mainline before v6.11.0 gets tagged.

Applied with Damien's Reviewed-by to pci/for-linus for v6.11, thanks.

> ---
>  drivers/pci/devres.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/pci/devres.c b/drivers/pci/devres.c
> index 3780a9f9ec00..c7affbbf73ab 100644
> --- a/drivers/pci/devres.c
> +++ b/drivers/pci/devres.c
> @@ -483,6 +483,8 @@ static void pcim_disable_device(void *pdev_raw)
>  
>  	if (!pdev->pinned)
>  		pci_disable_device(pdev);
> +
> +	pdev->is_managed = false;
>  }
>  
>  /**
> -- 
> 2.46.0
>