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

[Philipp Stanner <pstanner@redhat.com>]

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@redhat.com>
Closes: https://lore.kernel.org/all/20240903094431.63551744.alex.williamson@redhat.com/
Suggested-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Philipp Stanner <pstanner@redhat.com>
Tested-by: Alex Williamson <alex.williamson@redhat.com>
---
@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.

P.
---
 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