[tip: irq/urgent] PCI/MSI: Prevent recursive locking in pci_msix_write_tph_tag()

["tip-bot2 for Himanshu Madhani" <tip-bot2@linutronix.de>]

The following commit has been merged into the irq/urgent branch of tip:

Commit-ID:     68ea85df15d111d82fc474cbe104174791169355
Gitweb:        https://git.kernel.org/tip/68ea85df15d111d82fc474cbe104174791169355
Author:        Himanshu Madhani <himanshu.madhani@oracle.com>
AuthorDate:    Tue, 08 Jul 2025 22:25:30 
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Thu, 10 Jul 2025 23:41:08 +02:00

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: d5124a9957b2 ("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
---
 drivers/pci/msi/msi.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/msi/msi.c b/drivers/pci/msi/msi.c
index 6ede55a..d686488 100644
--- a/drivers/pci/msi/msi.c
+++ b/drivers/pci/msi/msi.c
@@ -934,10 +934,12 @@ 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