linux-kernel - Re: [PATCH v3] NFSv4: replace seqcount_t with a rw

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Date:   Wed, 2 Nov 2016 17:37:37 +0000
From:   Trond Myklebust <trondmy@...marydata.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
CC:     Schumaker Anna <anna.schumaker@...app.com>,
        List Linux NFS Mailing <linux-nfs@...r.kernel.org>,
        List Linux Kernel Mailing <linux-kernel@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>
Subject: Re: [PATCH v3] NFSv4: replace seqcount_t with a rw_semaphore


> On Nov 2, 2016, at 13:11, Sebastian Andrzej Siewior <bigeasy@...utronix.de> wrote:
> 
> On 2016-10-31 16:11:02 [+0000], Trond Myklebust wrote:
>> 
>> Yes, and yes. We can’t rely on the list pointers remaining correct, so we restart the list scan and we use the ops->state_flag_bit to signal whether or not state has been recovered for the entry being scanned.
> 
> but this is tested at the top of the loop and by then you look at
> lists' ->next pointer which might be invalid.
> 

No. We ensure we restart the list scan if we release the spinlock. It’s safe…