From: Robert Love <rml@ximian.com>
To: Ed L Cashin <ecashin@uga.edu>
Cc: linux-mm@kvack.org
Subject: Re: Documentation/vm/locking: why not hold two PT locks?
Date: Sun, 08 Feb 2004 17:12:00 -0500 [thread overview]
Message-ID: <1076278320.6015.1.camel@localhost> (raw)
In-Reply-To: <87ekt5ckgu.fsf@cs.uga.edu>
On Sun, 2004-02-08 at 16:47 -0500, Ed L Cashin wrote:
> If that's all there is to it, then in my case, I have imposed a
> locking hierarchy on my own code, so that wouldn't happen in my code.
> I have a semaphore "S" outside of mmap_sem and page_table_lock. Every
> call path that can get to my code takes S before getting the
> mmap_sem.
Well, you don't follow a locking hierarchy either, you just have a
global synchronizer (your semaphore S). Same effect, sure, you cannot
deadlock.
But anyone else who touches two or more PT's will deadlock.
> So it looks like my code is safe but not so efficient, since T2 has to
> sleep when it doesn't get the semaphore S. Is there some other
> complication I'm missing?
It could be that _I_ am missing something, and there is another reason
why we don't grab more than one PT concurrently. But the locking
hierarchy is still a concern.
Robert Love
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next prev parent reply other threads:[~2004-02-08 22:12 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-02-08 21:18 Ed L Cashin
2004-02-08 21:29 ` Robert Love
2004-02-08 21:47 ` Ed L Cashin
2004-02-08 22:12 ` Robert Love [this message]
2004-02-09 7:44 ` Kanoj Sarcar
2004-02-09 16:19 ` Ed L Cashin
2004-02-09 18:20 ` Kanoj Sarcar
2004-02-09 21:17 ` Ed L Cashin
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