linux-kernel - Re: [PATCH] arm64: ftrace: stop using kstop

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Message-ID: <20151203100750.1d612e1b@gandalf.local.home>
Date:	Thu, 3 Dec 2015 10:07:50 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Will Deacon <will.deacon@....com>
Cc:	libin <huawei.libin@...wei.com>, mingo@...hat.com,
	catalin.marinas@....com, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, guohanjun@...wei.com,
	dingtianhong@...wei.com
Subject: Re: [PATCH] arm64: ftrace: stop using kstop_machine to
 enable/disable tracing

On Thu, 3 Dec 2015 11:48:24 +0000
Will Deacon <will.deacon@....com> wrote:

> Hmm, so this should all be fine if we exclusively use the probe_kernel_*
> functions and handle the -EFAULT gracefully. Now, that leaves an
> interesting scenario with the flush_icache_range call in
> aarch64_insn_patch_text_nosync, since that's not run with
> KERNEL_DS/pagefault_disable() and so we'll panic if the text disappears
> underneath us.

Nothing should remove the text from underneath you if everything
matches up fine before that. Module unloading will block on the
ftrace_lock if it has any functions that can be traced.

-- Steve


> 
> So we probably need to add that code and call __flush_cache_user_range
> instead.
> 
> What do you think?
> 
> Will

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