linux-kernel - Re: BUG?: super.c:sget spin

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Message-ID: <CA+jWvaJech43W4DXNy-YJHq=rngfmKP__mnQ3Rtt+8hF5ru0fQ@mail.gmail.com>
Date:	Fri, 30 May 2014 01:37:55 +0200
From:	Kai <wildex999@...il.com>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: BUG?: super.c:sget spin_lock not released?

On Fri, May 30, 2014 at 1:19 AM, Al Viro <viro@...iv.linux.org.uk> wrote:
> On Fri, May 30, 2014 at 12:49:56AM +0200, Kai wrote:
>> Hello,
>>
>> I have recently been playing around with writing a custom filesystem
>> for Linux, and have been reading the source of other filesystems, and
>> the functions they call into the linux kernel.
>> While looking at the function sget in super.c I found something strange.
>>
>> before if(test) it takes a spinlock, however there seems to be two
>> cases where it does not unlock it.
>> (Kernel 3.14, super.c line 441)
>>
>> One:
>> if(!grab_super(old)) goto retry;
>> Will jump to before spin_lock(), without releasing it first.
>
> Er...  So either grab_super() releases that spinlock, or that thing
> is screwed.  The next obvious step would be to look into grab_super()...
>
>> Two:
>> And if it finds an old sb, it will return without releasing the lock.
>
> ... unless something it calls does just that.

AH, I knew I was missing something. And so obvious too =(

Thank you for pointing it out to me.
Seems I need to spend more time reading the source code and figuring
out how it all connects.
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