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Date: Thu, 7 May 2015 16:08:49 +0530
From: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
        Anton Arapov <arapov@gmail.com>, David Long <dave.long@linaro.org>,
        Denys Vlasenko <dvlasenk@redhat.com>,
        "Frank Ch. Eigler" <fche@redhat.com>, Ingo Molnar <mingo@kernel.org>,
        Jan Willeke <willeke@de.ibm.com>, Jim Keniston <jkenisto@us.ibm.com>,
        Mark Wielaard <mjw@redhat.com>, Pratyush Anand <panand@redhat.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 08/10] uprobes: Change handle_trampoline() to flush the
 frames invalidated by longjmp()
Message-ID: <20150507103849.GE30396@linux.vnet.ibm.com>
Reply-To: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
References: <20150504124835.GA22462@redhat.com>
 <20150504124918.GA22519@redhat.com>
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* Oleg Nesterov <oleg@redhat.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 return, so when func_1() returns the kernel uses the no longer valid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@redhat.com>
> ---

Looks good to me.

Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
-- 
Thanks and Regards
Srikar Dronamraju