PCI/MSI: Prevent recursive locking in pci_msix_write_tph_tag()

JIRA: https://issues.redhat.com/browse/RHEL-120705
Upstream Status: 68ea85d

commit 68ea85d
Author: Himanshu Madhani <himanshu.madhani@oracle.com>
Date:   Tue Jul 8 22:25:30 2025 +0000

    PCI/MSI: Prevent recursive locking in pci_msix_write_tph_tag()

    pci_msix_write_tph_tag() takes the per device MSI descriptor mutex and then
    invokes msi_domain_get_virq(), which takes the same mutex again. That
    obviously results in a system hang which is exposed by a softlockup or
    lockdep warning.

    Move the lock guard after the invocation of msi_domain_get_virq() to fix
    this.

    [ tglx: Massage changelog by adding a proper explanation and removing the
            not really useful stacktrace ]

    Fixes: d5124a9 ("PCI/MSI: Provide a sane mechanism for TPH")
    Reported-by: Jorge Lopez <jorge.jo.lopez@oracle.com>
    Suggested-by: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: Himanshu Madhani <himanshu.madhani@oracle.com>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Tested-by: Jorge Lopez <jorge.jo.lopez@oracle.com>
    Link: https://lore.kernel.org/all/20250708222530.1041477-1-himanshu.madhani@oracle.com

Signed-off-by: Myron Stowe <mstowe@redhat.com>

Author: Myron Stowe

drivers/pci/msi/msi.c

@@ -931,10 +931,12 @@ int pci_msix_write_tph_tag(struct pci_dev *pdev, unsigned int index, u16 tag)
 	if (!pdev->msix_enabled)
 		return -ENXIO;
 
-	guard(msi_descs_lock)(&pdev->dev);
 	virq = msi_get_virq(&pdev->dev, index);
 	if (!virq)
 		return -ENXIO;
+
+	guard(msi_descs_lock)(&pdev->dev);
+
 	/*
 	 * This is a horrible hack, but short of implementing a PCI
 	 * specific interrupt chip callback and a huge pile of