linux-kernel - Re: [PATCH 1/3] uprobes: install_breakpoint() should fail if is_swbp

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Date:	Sat, 2 Jun 2012 20:21:58 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Anton Arapov <anton@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] uprobes: install_breakpoint() should fail if
	is_swbp_insn() == T

On 06/01, Oleg Nesterov wrote:
>
> 	while (more--) {
> 		info = kmalloc(sizeof(struct map_info), GFP_KERNEL);
> 		if (!info) {
> 			curr = ERR_PTR(-ENOMEM);
> 			goto out;
> 		}
> 		info->next = prev;
> 		prev = info;
> 	}

This should be "do ... while (--more)", otherwise it seems to work
and really helps.

I did the simple test under qemu. Currently uprobe_register() hangs
"forever" if the probed addr has 10000 mappings, I'have stopped qemu
after several minutes.

With the new code uprobe_register() needs 0.403s to complete.

We can also change build_map_info() to try GFP_NOWAIT | GFP_NOMEMALLOC
under i_mmap_mutex first, not sure this is really needed.

I'll write the changelog and send the patch...

Do you see any problems with this approach?

Oleg.

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