From: "Chuck Lever" <chucklever@gmail.com>
Subject: Re: [patch 0/4] correct kernel locking for RPC rpc_release
	callbacks
Date: Wed, 18 Oct 2006 16:22:03 -0400
Message-ID: <76bd70e30610181322j639e1ea9ifb5965cb61612934@mail.gmail.com>
References: <1161105870.3315.20.camel@dyn9047022153>
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Cc: NFS List <nfs@lists.sourceforge.net>
To: "Frank Filz" <ffilzlnx@us.ibm.com>
In-Reply-To: <1161105870.3315.20.camel@dyn9047022153>
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On 10/17/06, Frank Filz <ffilzlnx@us.ibm.com> wrote:
> The following set of patches corrects use of the big kernel lock in
> protecting RPC calls and associated call backs.
>
> A problem was noted where nfs_async_unlink_release() was called without
> the BKL being held as expected. Chuck Lever and Trond Myklebust noted
> that the rpc_release() callback is a recent addition and other callbacks
> might also expect the BKL to be held.
>
> With the addition of lock_kernel()/unlock_kernel() around all calls to
> the rpc_release() callbacks, there is no need for NFS code to hold the
> BKL when making calls to rpc_execute(), rpc_call_sync(), and
> rpc_call_async().

I spent a little time looking at these, and they look reasonable to
me.  I didn't see any paths that were now exposed by removing the BKL,
but I'm not the most rigorous reviewer.

I am a little concerned that the RPC scheduler is taking and dropping
such a heavy-weight serialization primitive multiple times per RPC.
Perhaps the next step should be removing the requirement for the
lock/unlock calls around the tk_action call to reduce this overhead.

-- 
"We who cut mere stones must always be envisioning cathedrals"
   -- Quarry worker's creed

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