linux-kernel - Re: [PATCH v2 1/4] mm/highmem: Fix kernel-doc warnings in highmem*.h

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Date:   Wed, 27 Apr 2022 07:28:13 +0200
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Ira Weiny <ira.weiny@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Will Deacon <will@...nel.org>,
        Peter Collingbourne <pcc@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>, linux-kernel@...r.kernel.org,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
        outreachy@...ts.linux.dev,
        "Acked-by : Mike Rapoport" <rppt@...ux.ibm.com>
Subject: Re: [PATCH v2 1/4] mm/highmem: Fix kernel-doc warnings in highmem*.h

On martedì 26 aprile 2022 13:04:42 CEST Sebastian Andrzej Siewior wrote:
> On 2022-04-26 11:43:03 [+0200], Fabio M. De Francesco wrote:
> 
> Either way, according to the code kmap_atomic() does not always disable
> preemption 

Hi Sebastian,

In my last email (for patch 4/4) I wrote that I would add a deprecation 
notice to kunmap_local() and would talk about thread locality in 
kmap_local_page(). I want to confirm that I'll do these changes in v3.

Then I closed that email asking if I was still overlooking something. 
Consider that I'm relatively new to kernel development and that it's just 
something I do in my spare time. So I was pretty sure I was still missing 
something :)

After reading again the code of kmap_atomic() (as you suggested - thanks!) 
I noted that you correctly say that kmap_atomic() does not always disables 
preemption (i.e., preemption is disabled only for !PREEMPT_RT kernel's  
configurations).

Therefore I'll also change the first sentence of kunmap_local() to the 
following:

"[It] Unmaps an address previously mapped by kmap_atomic() and re-enables 
pagefaults and preemption (the latter disabled only for !PREEMP_RT 
configurations).".

I will also be making this change in v3.

Can you please say if I'm still missing something?

Thanks,

Fabio