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

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Message-ID: <20120802175312.GB11933@redhat.com>
Date:	Thu, 2 Aug 2012 19:53:12 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.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

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" ?

Yet another reason to move arch_uprobe_analyze_insn/etc to _register.

Oleg.

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