linux-kernel - Re: [PATCH] arm64/cpufeature: Convert hook_lock to raw_spin_lock_t in cpu_enable

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Message-ID: <20190604134901.GE6610@arrakis.emea.arm.com>
Date:   Tue, 4 Jun 2019 14:49:01 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Julien Grall <julien.grall@....com>
Cc:     linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, tglx@...utronix.de,
        rostedt@...dmis.org, bigeasy@...utronix.de, suzuki.poulose@....com,
        will.deacon@....com, dave.martin@....com
Subject: Re: [PATCH] arm64/cpufeature: Convert hook_lock to raw_spin_lock_t
 in cpu_enable_ssbs()

On Thu, May 30, 2019 at 12:30:58PM +0100, Julien Grall wrote:
> cpu_enable_ssbs() is called via stop_machine() as part of the cpu_enable
> callback. A spin lock is used to ensure the hook is registered before
> the rest of the callback is executed.
> 
> On -RT spin_lock() may sleep. However, all the callees in stop_machine()
> are expected to not sleep. Therefore a raw_spin_lock() is required here.
> 
> Given this is already done under stop_machine() and the work done under
> the lock is quite small, the latency should not increase too much.
> 
> Signed-off-by: Julien Grall <julien.grall@....com>

Queued for 5.3. Thanks.

-- 
Catalin