linux-kernel - Re: [PATCH v2 2.6.38-rc8-tip 3/20] 3: uprobes: Breakground page replacement.

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Message-ID: <20110314173004.GQ24254@linux.vnet.ibm.com>
Date:	Mon, 14 Mar 2011 23:00:04 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Stephen Wilson <wilsons@...rt.ca>
Cc:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linux-mm <linux-mm@...ck.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Christoph Hellwig <hch@...radead.org>,
	Andi Kleen <andi@...stfloor.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Oleg Nesterov <oleg@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...k.frob.com>,
	SystemTap <systemtap@...rces.redhat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH v2 2.6.38-rc8-tip 3/20]  3: uprobes: Breakground page
 replacement.

* Stephen Wilson <wilsons@...rt.ca> [2011-03-14 12:58:18]:

> On Mon, Mar 14, 2011 at 07:04:33PM +0530, Srikar Dronamraju wrote:
> > +/**
> > + * read_opcode - read the opcode at a given virtual address.
> > + * @tsk: the probed task.
> > + * @vaddr: the virtual address to store the opcode.
> > + * @opcode: location to store the read opcode.
> > + *
> > + * For task @tsk, read the opcode at @vaddr and store it in @opcode.
> > + * Return 0 (success) or a negative errno.
> > + */
> > +int __weak read_opcode(struct task_struct *tsk, unsigned long vaddr,
> > +						uprobe_opcode_t *opcode)
> > +{
> > +	struct vm_area_struct *vma;
> > +	struct page *page;
> > +	void *vaddr_new;
> > +	int ret;
> > +
> > +	ret = get_user_pages(tsk, tsk->mm, vaddr, 1, 0, 0, &page, &vma);
> > +	if (ret <= 0)
> > +		return -EFAULT;
> > +	ret = -EFAULT;
> > +
> > +	/*
> > +	 * check if the page we are interested is read-only mapped
> > +	 * Since we are interested in text pages, Our pages of interest
> > +	 * should be mapped read-only.
> > +	 */
> > +	if ((vma->vm_flags & (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)) ==
> > +						(VM_READ|VM_EXEC))
> > +		goto put_out;
> > +
> > +	lock_page(page);
> > +	vaddr_new = kmap_atomic(page, KM_USER0);
> > +	vaddr &= ~PAGE_MASK;
> > +	memcpy(&opcode, vaddr_new + vaddr, uprobe_opcode_sz);
> > +	kunmap_atomic(vaddr_new, KM_USER0);
> > +	unlock_page(page);
> > +	ret =  uprobe_opcode_sz;
> 
> This looks wrong.  We should be setting ret = 0 on success here?

Right, I should have set ret = 0 here.

> 
> > +
> > +put_out:
> > +	put_page(page); /* we did a get_page in the beginning */
> > +	return ret;
> > +}
> 
> -- 
> steve
> 
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