linux-kernel - Re: [RFC PATCH v4 4/6] uretprobes: return probe entry, prepare uretprobe

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Date:	Tue, 5 Mar 2013 14:20:55 +0100
From:	Anton Arapov <anton@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Josh Stone <jistone@...hat.com>,
	Frank Eigler <fche@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>
Subject: Re: [RFC PATCH v4 4/6] uretprobes: return probe entry, prepare
 uretprobe

On Mon, Mar 04, 2013 at 05:47:53PM +0100, Oleg Nesterov wrote:
> On 03/04, Anton Arapov wrote:
> >
> > @@ -1085,6 +1093,7 @@ static int xol_add_vma(struct xol_area *area)
> >  {
> >  	struct mm_struct *mm = current->mm;
> >  	int ret = -EALREADY;
> > +	uprobe_opcode_t insn = UPROBE_SWBP_INSN;
> >
> >  	down_write(&mm->mmap_sem);
> >  	if (mm->uprobes_state.xol_area)
> > @@ -1106,6 +1115,13 @@ static int xol_add_vma(struct xol_area *area)
> >  	smp_wmb();	/* pairs with get_xol_area() */
> >  	mm->uprobes_state.xol_area = area;
> >  	ret = 0;
> > +
> > +	/*
> > +	 * If we reached this place, we did allocate a new area. We want
> > +	 * pre-alloc a slot for the return probes here.
> > +	 */
> > +	xol_get_insn_slot(&insn);
> Just change get_xol_area() to do set_bit(0, bitmap) and copy_to_page(page, int3)
> (extacted from xol_get_insn_slot().
ah yes, right. Thanks for this hint.

> 
> > @@ -1485,8 +1538,11 @@ static struct uprobe *find_active_uprobe(unsigned long bp_vaddr, int *is_swbp)
> >  		*is_swbp = -EFAULT;
> >  	}
> >  
> > -	if (!uprobe && test_and_clear_bit(MMF_RECALC_UPROBES, &mm->flags))
> > +	utask = get_utask();
> > +	if (!uprobe && hlist_empty(&utask->return_uprobes) &&
> > +	    test_and_clear_bit(MMF_RECALC_UPROBES, &mm->flags)) {
> >  		mmf_recalc_uprobes(mm);
> Wait, I was wrong. We should not clear MMF_* if another thread has
> ->return_uprobes. Perhaps we should change uprobe_pre_sstep_notifier()
> instead...
Will look into it.

> >  	down_read(&uprobe->register_rwsem);
> >  	for (uc = uprobe->consumers; uc; uc = uc->next) {
> > -		int rc = uc->handler(uc, regs);
> > +		if (uc->handler)
> > +			rc = uc->handler(uc, regs);
> > +
> > +		if (uc->rp_handler)
> > +			prepare_uretprobe(uprobe, regs); /* put bp at return */
> Again, this is not right. We should do this only once after the main
> loop.
fixed for v5.

Thanks!
Anton.
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