[PATCH] PCI: Avoid possible deadlock on pci_lock and p->pi_lock

Path	csiph.com!aioe.org!news.servidellagleba.it!bofh.it!news.nic.it!robomod
From	Bjorn Helgaas <bhelgaas@google.com>
Newsgroups	linux.kernel
Subject	[PATCH] PCI: Avoid possible deadlock on pci_lock and p->pi_lock
Date	Thu, 19 Jan 2017 00:50:02 +0100
Message-ID	<t189j-2dy-9@gated-at.bofh.it> (permalink)
User-Agent	StGit/0.17.1-dirty
MIME-Version	1.0
Content-Type	text/plain; charset="utf-8"
Content-Transfer-Encoding	7bit
Sender	robomod@news.nic.it
List-ID	<linux-kernel.vger.kernel.org>
X-Mailing-List	linux-kernel@vger.kernel.org
Approved	robomod@news.nic.it
Lines	33
Organization	linux.* mail to news gateway
X-Original-Cc	Jan Kiszka <jan.kiszka@siemens.com>, linux-kernel@vger.kernel.org, Matthew Wilcox <mawilcox@microsoft.com>
X-Original-Date	Wed, 18 Jan 2017 17:46:12 -0600
X-Original-Message-ID	<20170118234612.26157.95913.stgit@bhelgaas-glaptop.roam.corp.google.com>
X-Original-Sender	linux-kernel-owner@vger.kernel.org
Xref	csiph.com linux.kernel:1562305

Show key headers only | View raw

pci_lock is an IRQ-safe spinlock that protects all accesses to PCI
configuration space (see PCI_OP_READ() and PCI_OP_WRITE() in pci/access.c).

The pci_cfg_access_unlock() path acquires pci_lock, then p->pi_lock (inside
wake_up_all()).  According to lockdep, there is a possible path involving
snbep_uncore_pci_read_counter() that could acquire them in the reverse
order: acquiring p->pi_lock, then pci_lock, which could result in a
deadlock.  Lockdep details are in the bugzilla below.

Avoid the possible deadlock by dropping pci_lock before waking up any
config access waiters.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=192901
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
---
 drivers/pci/access.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/access.c b/drivers/pci/access.c
index db239547fefd..68bd7201d8bc 100644
--- a/drivers/pci/access.c
+++ b/drivers/pci/access.c
@@ -684,8 +684,9 @@ void pci_cfg_access_unlock(struct pci_dev *dev)
 	WARN_ON(!dev->block_cfg_access);
 
 	dev->block_cfg_access = 0;
-	wake_up_all(&pci_cfg_wait);
 	raw_spin_unlock_irqrestore(&pci_lock, flags);
+
+	wake_up_all(&pci_cfg_wait);
 }
 EXPORT_SYMBOL_GPL(pci_cfg_access_unlock);

Back to linux.kernel | Previous | Next | Find similar | Unroll thread

Thread

[PATCH] PCI: Avoid possible deadlock on pci_lock and p->pi_lock Bjorn Helgaas <bhelgaas@google.com> - 2017-01-19 00:50 +0100

csiph-web