linux-kernel - Re: [PATCH v2 1/2] uprobes: Pass probed vaddr to arch_uprobe_analyze

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Date:	Mon, 11 Jun 2012 18:12:15 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Ananth N Mavinakayanahalli <ananth@...ibm.com>
Cc:	linuxppc-dev@...ts.ozlabs.org, lkml <linux-kernel@...r.kernel.org>,
	michael@...erman.id.au, antonb@...nktux.localdomain,
	Paul Mackerras <paulus@...ba.org>, benh@...nel.crashing.org,
	Ingo Molnar <mingo@...e.hu>, peterz@...radead.org,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Jim Keniston <jkenisto@...ibm.com>
Subject: Re: [PATCH v2 1/2] uprobes: Pass probed vaddr to
	arch_uprobe_analyze_insn()

Ananth, Srikar,

I think the patch is correct and I am sorry for nit-picking,
this is really minor.

But,

On 06/08, Ananth N Mavinakayanahalli wrote:
>
> Changes in V2:
> Pass (unsigned long)addr

Well, IMHO, this is confusing.

First of all, why do we have this "addr" or even "vaddr"? It should
not exists. We pass it to copy_insn(), but for what?? copy_insn()
should simply use uprobe->offset, the virtual address for this
particular mapping does not matter at all. I am going to send
the cleanup.

Note also that we should move this !UPROBE_COPY_INSN from
install_breakpoint() to somewhere near alloc_uprobe(). This code
is called only once, it looks a bit strange to use the "random" mm
(the first mm vma_prio_tree_foreach() finds) and its mapping to
verify the insn. In fact this is simply not correct and should be
fixed, note that on x86 arch_uprobe_analyze_insn() checks
mm->context.ia32_compat.

IOW, Perhaps uprobe->offset makes more sense?

> --- linux-3.5-rc1.orig/kernel/events/uprobes.c
> +++ linux-3.5-rc1/kernel/events/uprobes.c
> @@ -697,7 +697,7 @@ install_breakpoint(struct uprobe *uprobe
>  		if (is_swbp_insn((uprobe_opcode_t *)uprobe->arch.insn))
>  			return -EEXIST;
>
> -		ret = arch_uprobe_analyze_insn(&uprobe->arch, mm);
> +		ret = arch_uprobe_analyze_insn(&uprobe->arch, mm, addr);

Just fyi, this conflicts with
"[PATCH 1/3] uprobes: install_breakpoint() should fail if is_swbp_insn() == T"
I sent, but the conflict is trivial.

Oleg.

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