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From: Josh Triplett <josh@joshtriplett.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: kbuild test robot <fengguang.wu@intel.com>,
	Ingo Molnar <mingo@kernel.org>,
	kbuild-all@01.org, linux-sparse@vger.kernel.org,
	sparse@chrisli.org
Subject: Re: [tip:sched/core 16/27] fs/jbd/commit.c:105:12: sparse: context imbalance in 'inverted_lock' - wrong count at exit
Date: Mon, 30 Sep 2013 08:25:51 -0700	[thread overview]
Message-ID: <20130930152550.GA1269@leaf> (raw)
In-Reply-To: <20130930134434.GC12926@twins.programming.kicks-ass.net>

On Mon, Sep 30, 2013 at 03:44:34PM +0200, Peter Zijlstra wrote:
> On Wed, Sep 25, 2013 at 02:47:20PM -0700, Josh Triplett wrote:
> > That's expressible in Sparse; look at how spin_trylock and _cond_lock,
> > and write a _cond_unlock.
> 
> Yeah, I know about __cond_lock() its an abomination that should die.

Can't argue with that.

> I
> did take a stab at teach sparse something saner but got stuck.. was
> years ago, can't remember more.

I only see two obvious ways to extend Sparse to remove the need for
__cond_lock, and only one makes sense.

First, you could add an attribute for conditional context changes, which
takes an expression; however, that would require an expression
evaluator, which internally would construct code a lot like __cond_lock,
and it would require some syntax to reference the return value.  That
seems excessively painful, and not significantly better than
__cond_lock.

Second, the real solution: teach Sparse to do whole-program
analysis, similar to GCC LTO.

Alternatively, someone could write a GCC plugin that understands the
context attribute and __context__ statement, and then does whole-program
context analysis using GCC; that seems easiest, relatively speaking.

- Josh Triplett

  reply	other threads:[~2013-09-30 15:26 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <52432bed.WfPoNUw4qxmYeQy4%fengguang.wu@intel.com>
2013-09-25 18:59 ` [tip:sched/core 16/27] fs/jbd/commit.c:105:12: sparse: context imbalance in 'inverted_lock' - wrong count at exit Peter Zijlstra
2013-09-25 21:47   ` Josh Triplett
2013-09-30 13:44     ` Peter Zijlstra
2013-09-30 15:25       ` Josh Triplett [this message]
2013-09-30 15:35         ` Peter Zijlstra
2013-09-25 21:58   ` Josh Triplett

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