linux-kernel - Re: [PATCH v5] arm64: kdump: simplify the reservation behaviour of crashkernel=,high

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Date:   Fri, 14 Apr 2023 15:34:16 +0100
From:   Will Deacon <will@...nel.org>
To:     Baoquan He <bhe@...hat.com>
Cc:     linux-kernel@...r.kernel.org, catalin.marinas@....com,
        horms@...nel.org, thunder.leizhen@...wei.com,
        John.p.donnelly@...cle.com, kexec@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v5] arm64: kdump: simplify the reservation behaviour of
 crashkernel=,high

Hi,

On Fri, Apr 07, 2023 at 10:24:19AM +0800, Baoquan He wrote:
> On arm64, reservation for 'crashkernel=xM,high' is taken by searching for
> suitable memory region top down. If the 'xM' of crashkernel high memory
> is reserved from high memory successfully, it will try to reserve
> crashkernel low memory later accoringly. Otherwise, it will try to search
> low memory area for the 'xM' suitable region. Please see the details in
> Documentation/admin-guide/kernel-parameters.txt.

[...]

>  arch/arm64/mm/init.c | 44 ++++++++++++++++++++++++++++++++++----------
>  1 file changed, 34 insertions(+), 10 deletions(-)

I tried to apply this, but smatch is unhappy with the result:

  | arch/arm64/mm/init.c:153 reserve_crashkernel() error: uninitialized symbol 'search_base'.

I _think_ this is a false positive, but I must say that the control flow
in reserve_crashkernel() is extremely hard to follow so I couldn't be
sure. If the static checker is struggling, then so will humans!

Ideally, this would all be restructured to make it easier to follow,
but in the short term we need something to squash the warning.

Cheers,

Will