linux-kernel - Re: [PATCH] uprobes: Ignore unsupported instructions in uprobe

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Date:	Fri, 3 Aug 2012 06:50:04 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Anton Arapov <anton@...hat.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	William Cohen <wcohen@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] uprobes: Ignore unsupported instructions in uprobe_mmap

* Oleg Nesterov <oleg@...hat.com> [2012-08-02 19:53:12]:

> On 08/02, Srikar Dronamraju wrote:
> >
> > * Oleg Nesterov <oleg@...hat.com> [2012-08-02 16:17:57]:
> >
> > > Forgot to mention...
> > >
> > > On 08/02, Srikar Dronamraju wrote:
> > > >
> > > > While at it, add a missing put_uprobe() in the path where uprobe_mmap()
> > > > races with uprobe_unregister().
> > > > ...
> > > > @@ -1051,8 +1051,10 @@ int uprobe_mmap(struct vm_area_struct *vma)
> > > >  			if (ret == -EEXIST) {
> > > >  				ret = 0;
> > > >
> > > > -				if (!is_swbp_at_addr(vma->vm_mm, vaddr))
> > > > +				if (!is_swbp_at_addr(vma->vm_mm, vaddr)) {
> > > > +					put_uprobe(uprobe);
> > > >  					continue;
> > > > +				}
> > >
> > > Yes, this part looks correct.
> > >
> > > In fact, I think this is not really correct anyway (wrt counter)
> > > but we are going to kill it.
> > >
> > >
> >
> > Are you expecting the counter to be decreased/increased here?
> 
> uprobes_state.count is very wrong, afaics. I'll try to send the fixes
> "soon", after we solve the pending problems (this one + stepping).
> 
> > This is case where the uprobe_mmap() and uprobe_unregister() raced, and
> > by the time install_breakpoint() was called by uprobe_mmap(), there were
> > no consumers.
> 
> Yes, exactly, and this case doesn't look 100% right too,
> 
> > i.e there are no uprobe->consumers and the underlying
> > instruction is still not a breakpoint instruction.
> 
> Yes, but what if it _IS_ "int3" ?

for int3, install_breakpoint returns -ENOTSUPP as install_breakpoint
does an explicit check if the instruction is breakpoint instruction 
and x86 analyse_insn() also returns -ENOTSUPP.

> 
> Yet another reason to move arch_uprobe_analyze_insn/etc to _register.
> 

I am for moving the stuff to _register that avoids us from looking at
these cases.

-- 
Thanks and Regards

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