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Message-ID: <20150507103849.GE30396@linux.vnet.ibm.com>
Date: Thu, 7 May 2015 16:08:49 +0530
From: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Ananth N Mavinakayanahalli <ananth@...ibm.com>,
Anton Arapov <arapov@...il.com>,
David Long <dave.long@...aro.org>,
Denys Vlasenko <dvlasenk@...hat.com>,
"Frank Ch. Eigler" <fche@...hat.com>,
Ingo Molnar <mingo@...nel.org>,
Jan Willeke <willeke@...ibm.com>,
Jim Keniston <jkenisto@...ibm.com>,
Mark Wielaard <mjw@...hat.com>,
Pratyush Anand <panand@...hat.com>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 08/10] uprobes: Change handle_trampoline() to flush the
frames invalidated by longjmp()
* Oleg Nesterov <oleg@...hat.com> [2015-05-04 14:49:18]:
>
> fails if you probe func_1() and func_2() because handle_trampoline()
> assumes that the probed function should must return and hit the bp
> installed be prepare_uretprobe(). But in this case func_2() does not
> return, so when func_1() returns the kernel uses the no longer valid
> return_instance of func_2().
>
> Change handle_trampoline() to unwind ->return_instances until we know
> that the next chain is alive or NULL, this ensures that the current
> chain is the last we need to report and free.
>
> Alternatively, every return_instance could use unique trampoline_vaddr,
> in this case we could use it as a key. And this could solve the problem
> with sigaltstack() automatically.
>
> But this approach needs more changes, and it puts the "hard" limit on
> MAX_URETPROBE_DEPTH. Plus it can not solve another problem partially
> fixed by the next patch.
>
> Note: this change has no effect on !x86, the arch-agnostic version of
> arch_uretprobe_is_alive() just returns "true".
>
> TODO: as documented by the previous change, arch_uretprobe_is_alive()
> can be fooled by sigaltstack/etc.
>
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
Looks good to me.
Acked-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
--
Thanks and Regards
Srikar Dronamraju
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