linux-kernel - [PATCH v2] pci: lock the pci_cfg_wait queue for the consistency of data

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Date:   Tue, 19 Nov 2019 09:15:45 +0800
From:   Xiang Zheng <zhengxiang9@...wei.com>
To:     <bhelgaas@...gle.com>, <willy@...radead.org>
CC:     <zhengxiang9@...wei.com>, <wangxiongfeng2@...wei.com>,
        <wanghaibin.wang@...wei.com>, <guoheyi@...wei.com>,
        <yebiaoxiang@...wei.com>, <linux-pci@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <rjw@...ysocki.net>,
        <tglx@...utronix.de>, <guohanjun@...wei.com>,
        <yangyingliang@...wei.com>
Subject: [PATCH v2] pci: lock the pci_cfg_wait queue for the consistency of data

Commit "7ea7e98fd8d0" suggests that the "pci_lock" is sufficient,
and all the callers of pci_wait_cfg() are wrapped with the "pci_lock".

However, since the commit "cdcb33f98244" merged, the accesses to
the pci_cfg_wait queue are not safe anymore. A "pci_lock" is
insufficient and we need to hold an additional queue lock while
read/write the wait queue.

So let's use the add_wait_queue()/remove_wait_queue() instead of
__add_wait_queue()/__remove_wait_queue(). Also move the wait queue
functionality around the "schedule()" function to avoid reintroducing
the deadlock addressed by "cdcb33f98244".

Signed-off-by: Xiang Zheng <zhengxiang9@...wei.com>
Cc: Heyi Guo <guoheyi@...wei.com>
Cc: Biaoxiang Ye <yebiaoxiang@...wei.com>
---

v2:
 - Move the wait queue functionality around the "schedule()" function to
   avoid reintroducing the deadlock addressed by "cdcb33f98244"

---

 drivers/pci/access.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/access.c b/drivers/pci/access.c
index 2fccb5762c76..09342a74e5ea 100644
--- a/drivers/pci/access.c
+++ b/drivers/pci/access.c
@@ -207,14 +207,14 @@ static noinline void pci_wait_cfg(struct pci_dev *dev)
 {
 	DECLARE_WAITQUEUE(wait, current);
 
-	__add_wait_queue(&pci_cfg_wait, &wait);
 	do {
 		set_current_state(TASK_UNINTERRUPTIBLE);
 		raw_spin_unlock_irq(&pci_lock);
+		add_wait_queue(&pci_cfg_wait, &wait);
 		schedule();
+		remove_wait_queue(&pci_cfg_wait, &wait);
 		raw_spin_lock_irq(&pci_lock);
 	} while (dev->block_cfg_access);
-	__remove_wait_queue(&pci_cfg_wait, &wait);
 }
 
 /* Returns 0 on success, negative values indicate error. */
-- 
2.19.1