linux-kernel - Re: [PATCH v7 3.2-rc2 4/30] uprobes: Define hooks for mmap/munmap.

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Message-ID: <20111201132406.GI18380@linux.vnet.ibm.com>
Date:	Thu, 1 Dec 2011 18:54:06 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux-mm <linux-mm@...ck.org>, Ingo Molnar <mingo@...e.hu>,
	Andi Kleen <andi@...stfloor.org>,
	Christoph Hellwig <hch@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Roland McGrath <roland@...k.frob.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Anton Arapov <anton@...hat.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Stephen Wilson <wilsons@...rt.ca>, tulasidhard@...il.com
Subject: Re: [PATCH v7 3.2-rc2 4/30] uprobes: Define hooks for mmap/munmap.

> > I was following the general convention being used within the kernel to not
> > bother about the area that we are going to unmap. For example: If a ptraced
> > area were to be unmapped or remapped, I dont see the breakpoint being
> > removed and added back. Also if a ptrace process is exitting, we dont go
> > about removing the installed breakpoints.
> > 
> > Also we would still need the check for EEXIST and read_opcode for handling
> > the fork() case. So even if we add extra line to remove the actual
> > breakpoint in munmap, It doesnt make the code any more simpler.
> 
> Not adding the counter now does though. The whole mm->mm_uprobes_count
> thing itself is basically an optimization.
> 
> Without it we'll get to uprobe_notify_resume() too often, but who cares.
> And not having to worry about it removes a lot of this complexity.
> 
> Then in the patch where you introduce this optimization you can list all
> the nitty gritty details of mremap/fork and counter balancing.
> 

Okay, I will move the optimization parts into a separate patch and keep
it at the end of the patchset.

> Another point, maybe add some comments on how the generic bits of
> uprobe_notify_resume()/uprobe_bkpt_notifier()/uprobe_post_notifier() etc
> hang together and what the arch stuff should do. 
> 
> Currently I have to flip back and forth between those to figure out what
> happens.
> 
> Having that information also helps validate that x86 does indeed do what
> is expected and helps other arch maintainers write their code without
> having to grok wtf x86 does.
> 

Okay, will work towards this.

-- 
Thanks and Regards
Srikar

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