linux-kernel - Re: [PATCH 2/3] resource: Include resource end in walk

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Message-ID: <20180928135439.GD21895@zn.tnic>
Date:   Fri, 28 Sep 2018 15:54:39 +0200
From:   Borislav Petkov <bp@...e.de>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Lianbo Jiang <lijiang@...hat.com>,
        Vivek Goyal <vgoyal@...hat.com>, kexec@...ts.infradead.org,
        tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        x86@...nel.org, akpm@...ux-foundation.org,
        dan.j.williams@...el.com, thomas.lendacky@....com,
        baiyaowei@...s.chinamobile.com, tiwai@...e.de,
        brijesh.singh@....com, dyoung@...hat.com, bhe@...hat.com
Subject: Re: [PATCH 2/3] resource: Include resource end in walk_*() interfaces

On Thu, Sep 27, 2018 at 09:22:02AM -0500, Bjorn Helgaas wrote:
> From: Bjorn Helgaas <bhelgaas@...gle.com>
> 
> find_next_iomem_res() finds an iomem resource that covers part of a range
> described by "start, end".  All callers expect that range to be inclusive,
> i.e., both start and end are included, but find_next_iomem_res() doesn't
> handle the end address correctly.
> 
> If it finds an iomem resource that contains exactly the end address, it
> skips it, e.g., if "start, end" is [0x0-0x10000] and there happens to be an
> iomem resource [mem 0x10000-0x10000] (the single byte at 0x10000), we skip
> it:
> 
>   find_next_iomem_res(...)
>   {
>     start = 0x0;
>     end = 0x10000;
>     for (p = next_resource(...)) {
>       # p->start = 0x10000;
>       # p->end = 0x10000;
>       # we *should* return this resource, but this condition is false:
>       if ((p->end >= start) && (p->start < end))
>         break;
> 
> Adjust find_next_iomem_res() so it allows a resource that includes the
> single byte at the end of the range.  This is a corner case that we
> probably don't see in practice.

This is how one should write commit messages! Thanks for that - it was a
joy - for a change - to read it :-)

> 
> Fixes: 58c1b5b07907 ("[PATCH] memory hotadd fixes: find_next_system_ram catch range fix")
> Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
> ---
>  kernel/resource.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

Reviewed-by: Borislav Petkov <bp@...e.de>

> diff --git a/kernel/resource.c b/kernel/resource.c
> index 30e1bc68503b..155ec873ea4d 100644
> --- a/kernel/resource.c
> +++ b/kernel/resource.c
> @@ -319,7 +319,7 @@ int release_resource(struct resource *old)
>  EXPORT_SYMBOL(release_resource);
>  
>  /*
> - * Finds the lowest iomem resource existing within [res->start.res->end).

What I'm still wondering about is, why was it ever even considered to
have a non-inclusive range. Looking at the git history, especially
58c1b5b07907 and 2842f11419704 - it looks like it was an omission and
then users started using it with inclusive ranges.

Thx.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)