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

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Date:   Tue, 26 Apr 2022 09:01:32 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>
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 2022-04-25 18:23:57 [+0200], Fabio M. De Francesco wrote:
> index a77be5630209..aa22daeed617 100644
> --- a/include/linux/highmem-internal.h
> +++ b/include/linux/highmem-internal.h
> @@ -236,9 +236,17 @@ static inline unsigned long totalhigh_pages(void) { return 0UL; }
>  
>  #endif /* CONFIG_HIGHMEM */
>  
> -/*
> - * Prevent people trying to call kunmap_atomic() as if it were kunmap()
> - * kunmap_atomic() should get the return value of kmap_atomic, not the page.
> +/**
> + * kunmap_atomic - Unmap the virtual address mapped by kmap_atomic()
> + * @__addr:       Virtual address to be unmapped
> + *
> + * Unmaps an address previously mapped by kmap_atomic() and re-enables
> + * pagefaults and preemption. Mappings should be unmapped in the reverse

You mind adding "Deprecated!" like kmap_atomic() has? The part about
disabling/ enabling preemption is true for !PREEMPT_RT. The part that
worries me is that people use it and rely on disabled preemption like
some did in the past. 
I've been told this API is about to be removed (or so I have been told)
so I hope that it will be gone soon ;)

> + * order that they were mapped. See kmap_local_page() for details.
> + * @__addr can be any address within the mapped page, so there is no need
> + * to subtract any offset that has been added. In contrast to kunmap(),
> + * this function takes the address returned from kmap_atomic(), not the
> + * page passed to it. The compiler will warn you if you pass the page.
>   */
>  #define kunmap_atomic(__addr)					\
>  do {								\

Sebastian