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

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Message-ID: <ZDnzJaqQLkllQox1@MiWiFi-R3L-srv>
Date:   Sat, 15 Apr 2023 08:43:17 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Will Deacon <will@...nel.org>
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

On 04/14/23 at 03:34pm, Will Deacon wrote:
> 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.

Sorry for that, I didn't run static checker. We should do initialization
as below to fix the warning. Below code can be added into this v5 patch,
or I can post v6 with Catalin's Reviewed-by tag.

Yes, about restructuring, I can think about it later. The added corner
cases handling specific for arm64 makes the flow a little harder to
flow. I will consider if adding document in arm64 is better.

>From 3575571ab9614c31f30933148a8693924a30321c Mon Sep 17 00:00:00 2001
From: Baoquan He <bhe@...hat.com>
Date: Sat, 15 Apr 2023 08:35:08 +0800
Subject: [PATCH] arm64: kdump: fix warning reported by static checker
Content-type: text/plain

Signed-off-by: Baoquan He <bhe@...hat.com>
---
 arch/arm64/mm/init.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 13750b0548da..bfc117cefcd5 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -128,9 +128,9 @@ static int __init reserve_crashkernel_low(unsigned long long low_size)
  */
 static void __init reserve_crashkernel(void)
 {
-	unsigned long long crash_base, crash_size, search_base;
+	unsigned long long crash_low_size = 0, search_base = 0;
 	unsigned long long crash_max = CRASH_ADDR_LOW_MAX;
-	unsigned long long crash_low_size = 0;
+	unsigned long long crash_base, crash_size;
 	char *cmdline = boot_command_line;
 	bool fixed_base = false;
 	bool high = false;
-- 
2.34.1