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

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Date:   Mon, 28 Oct 2019 09:30:41 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Xiang Zheng <zhengxiang9@...wei.com>
Cc:     bhelgaas@...gle.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: Re: [PATCH] pci: lock the pci_cfg_wait queue for the consistency of
 data

On Mon, Oct 28, 2019 at 05:18:09PM +0800, Xiang Zheng wrote:
> 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().

As I said earlier, this reintroduces the deadlock addressed by
cdcb33f9824429a926b971bf041a6cec238f91ff