linux-kernel - Re: [PATCH v2] clk: tegra: Use readl_relaxed_poll_timeout_atomic in tegra210_clock

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Date:   Thu, 19 Oct 2017 11:44:22 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Nicolin Chen <nicoleotsuka@...il.com>
Cc:     sboyd@...eaurora.org, pdeschrijver@...dia.com,
        linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-clk@...r.kernel.org, jonathanh@...dia.com,
        mturquette@...libre.com, pgaikwad@...dia.com
Subject: Re: [PATCH v2] clk: tegra: Use readl_relaxed_poll_timeout_atomic in
 tegra210_clock_init

On Thu, Oct 19, 2017 at 02:29:20AM -0700, Nicolin Chen wrote:
> On Fri, Sep 15, 2017 at 12:10:13PM -0700, Nicolin Chen wrote:
> > Below is the call trace of tegra210_init_pllu() function:
> >   start_kernel()
> >   -> time_init()
> >   --> of_clk_init()
> >   ---> tegra210_clock_init()
> >   ----> tegra210_pll_init()
> >   -----> tegra210_init_pllu()
> > 
> > Because the preemption is disabled in the start_kernel before calling
> > time_init, tegra210_init_pllu is actually in an atomic context while
> > it includes a readl_relaxed_poll_timeout that might sleep.
> > 
> > So this patch just changes this readl_relaxed_poll_timeout() to its
> > atomic version.
> > 
> > Signed-off-by: Nicolin Chen <nicoleotsuka@...il.com>
> > Acked-By: Peter De Schrijver <pdeschrijver@...dia.com>
> 
> Thierry, can you also take a look at this one? I sent a month ago. Thanks.

I'm wondering why we're not seeing a splat for this. Usually the kernel
will warn if you sleep during atomic context. Does this mean we're just
not hitting that case? readx_poll_timeout() has a might_sleep_if(), and
therefore it should always cause the splat.

Any ideas why this has gone unnoticed for all this time?

Thierry

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