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

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Date:	Fri, 30 May 2014 00:49:56 +0200
From:	Kai <wildex999@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: BUG?: super.c:sget spin_lock not released?

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.

Two:
And if it finds an old sb, it will return without releasing the lock.

This code seems to be the same in 3.14 and in 2.6
I might just be missing how the spin_lock works, and if so I'm sorry.
But this seems really strange to me. Would this not potentially cause
a deadlock on sb_lock?
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