linux-kernel - Re: [PATCH v5 3.1.0-rc4-tip 0/26] Uprobes patchset with perf probe support

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Date:	Tue, 20 Sep 2011 19:42:04 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linux-mm <linux-mm@...ck.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jonathan Corbet <corbet@....net>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Hugh Dickins <hughd@...gle.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andi Kleen <andi@...stfloor.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...k.frob.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 3.1.0-rc4-tip 0/26]   Uprobes patchset with perf
 probe support

* Christoph Hellwig <hch@...radead.org> [2011-09-20 09:34:01]:

> On Tue, Sep 20, 2011 at 05:29:38PM +0530, Srikar Dronamraju wrote:
> > - Uses i_mutex instead of uprobes_mutex.
> 
> What for exactly?  I'm pretty strict against introducing even more
> uses for i_mutex, it's already way to overloaded with different
> meanings.
> 

There could be multiple simultaneous requests for adding/removing a
probe for the same location i.e same inode + same offset. These requests
will have to be serialized.

To serialize this we had used uprobes specific mutex (uprobes_mutex) in
the last patchset.  However using uprobes_mutex will mean we will be
serializing requests for unrelated files. I.e if we get a request to
probe libpthread while we are inserting/deleting a probe on libc, 
then we used to make the libpthread request wait unnecessarily.
This also means that I dont need to introduce yet another lock.

After using i_mutex, these two requests can run in parallel.

I had proposed this while answering one of the comments in the last
patchset. Since I didnt hear any complaints, I went ahead and
implemented this.

I could use any other inode/file/mapping based sleepable lock that is of
higher order than mmap_sem. Can you please let me know if we have
alternatives.

-- 
Thanks and Regards
Srikar

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