linux-kernel - Re: [PATCH v15 07/13] arm64: factor work

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Date:	Wed, 17 Aug 2016 09:05:31 +0100
From:	Will Deacon <will.deacon@....com>
To:	Chris Metcalf <cmetcalf@...lanox.com>
Cc:	Gilad Ben Yossef <giladb@...lanox.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>, Tejun Heo <tj@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Christoph Lameter <cl@...ux.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Andy Lutomirski <luto@...capital.net>,
	Mark Rutland <mark.rutland@....com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v15 07/13] arm64: factor work_pending state machine to C

Hi Chris,

On Tue, Aug 16, 2016 at 05:19:30PM -0400, Chris Metcalf wrote:
> Currently ret_fast_syscall, work_pending, and ret_to_user form an ad-hoc
> state machine that can be difficult to reason about due to duplicated
> code and a large number of branch targets.
> 
> This patch factors the common logic out into the existing
> do_notify_resume function, converting the code to C in the process,
> making the code more legible.
> 
> This patch tries to closely mirror the existing behaviour while using
> the usual C control flow primitives. As local_irq_{disable,enable} may
> be instrumented, we balance exception entry (where we will almost most
> likely enable IRQs) with a call to trace_hardirqs_on just before the
> return to userspace.
> 
> Signed-off-by: Chris Metcalf <cmetcalf@...lanox.com>
> ---
>  arch/arm64/kernel/entry.S  | 12 ++++--------
>  arch/arm64/kernel/signal.c | 36 ++++++++++++++++++++++++++----------
>  2 files changed, 30 insertions(+), 18 deletions(-)

I plan to queue this one in the arm64 tree for 4.9. Should hit -next
sometime next week.

Will