linux-kernel - Re: [PATCH -next] crash: Fix riscv64 crash memory reserve dead loop

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Message-ID: <ZrXmqyhalkcY-wpx@arm.com>
Date: Fri, 9 Aug 2024 10:51:39 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Jinjie Ruan <ruanjinjie@...wei.com>
Cc: Baoquan He <bhe@...hat.com>, vgoyal@...hat.com, dyoung@...hat.com,
	paul.walmsley@...ive.com, palmer@...belt.com, aou@...s.berkeley.edu,
	chenjiahao16@...wei.com, akpm@...ux-foundation.org,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-riscv@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org, Will Deacon <will@...nel.org>
Subject: Re: [PATCH -next] crash: Fix riscv64 crash memory reserve dead loop

On Thu, Aug 08, 2024 at 03:56:35PM +0800, Jinjie Ruan wrote:
> On 2024/8/7 3:34, Catalin Marinas wrote:
> > On Tue, Aug 06, 2024 at 08:10:30PM +0100, Catalin Marinas wrote:
> >> On Fri, Aug 02, 2024 at 06:11:01PM +0800, Baoquan He wrote:
> >>> And I don't like the idea crashkernel=,high failure will fallback to
> >>> attempt in low area, so this looks good to me.
> >>
> >> Well, I kind of liked this behaviour. One can specify ,high as a
> >> preference rather than forcing a range. The arm64 land has different
> >> platforms with some constrained memory layouts. Such fallback works well
> >> as a default command line option shipped with distros without having to
> >> guess the SoC memory layout.
> > 
> > I haven't tried but it's possible that this patch also breaks those
> > arm64 platforms with all RAM above 4GB when CRASH_ADDR_LOW_MAX is
> > memblock_end_of_DRAM(). Here all memory would be low and in the absence
> > of no fallback, it fails to allocate.
> > 
> > So, my strong preference would be to re-instate the current behaviour
> > and work around the infinite loop in a different way.
> 
> Hi, baoquan, What's your opinion?
> 
> Only this patch should be re-instate or all the 3 dead loop fix patch?

Only the riscv64 patch that that removes the ,high reservation fallback
to ,low. From this series:

https://lore.kernel.org/r/20240719095735.1912878-1-ruanjinjie@huawei.com/

the first two fixes look fine (x86_32). The third one (arm32), not sure
why it's in the series called "crash: Fix x86_32 memory reserve dead
loop bug". Does it fix a problem on arm32? Anyway, I'm not against it
getting merged but I'm not maintaining arm32. If the first two patches
could be merged for 6.11, I think the arm32 one is more of a 6.12
material (unless it does fix something).

On the riscv64 patch removing the high->low fallback to avoid the
infinite loop, I'd rather replace it with something similar to the
x86_32 fix in the series above. I suggested something in the main if
block but, looking at the x86_32 fix, for consistency, I think it would
look better as something like:

diff --git a/kernel/crash_reserve.c b/kernel/crash_reserve.c
index d3b4cd12bdd1..64d44a52c011 100644
--- a/kernel/crash_reserve.c
+++ b/kernel/crash_reserve.c
@@ -423,7 +423,8 @@ void __init reserve_crashkernel_generic(char *cmdline,
 		if (high && search_end == CRASH_ADDR_HIGH_MAX) {
 			search_end = CRASH_ADDR_LOW_MAX;
 			search_base = 0;
-			goto retry;
+			if (search_end != CRASH_ADDR_HIGH_MAX)
+				goto retry;
 		}
 		pr_warn("cannot allocate crashkernel (size:0x%llx)\n",
 			crash_size);

In summary, just replace the riscv64 fix with something along the lines
of the diff above (or pick whatever you prefer that still keeps the
fallback).

Thanks.

-- 
Catalin