linux-kernel - [PATCH] PCI: Fix might_sleep() lockdep warning in pcim

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Message-ID: <20240904072541.8746-2-pstanner@redhat.com>
Date: Wed,  4 Sep 2024 09:25:42 +0200
From: Philipp Stanner <pstanner@...hat.com>
To: Bjorn Helgaas <bhelgaas@...gle.com>,
	Krzysztof Wilczyński <kwilczynski@...nel.org>,
	Philipp Stanner <pstanner@...hat.com>,
	Damien Le Moal <dlemoal@...nel.org>,
	Alex Williamson <alex.williamson@...hat.com>
Cc: linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] PCI: Fix might_sleep() lockdep warning in pcim_intx()

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.

Under some circumstances it can happen that drivers share a struct
pci_dev. 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.

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 not run implicitly into managed code.

Fixes: 25216afc9db5 ("PCI: Add managed pcim_intx()")
Reported-by: Alex Williamson <alex.williamson@...hat.com>
Closes: https://lore.kernel.org/all/20240903094431.63551744.alex.williamson@redhat.com/
Signed-off-by: Philipp Stanner <pstanner@...hat.com>
---
@Alex:
Please have a look whether this fixes your issue.

Might also be cool to include your lockdep warning in the commit
message, if you can provide that.

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