Re: [PATCH -next v2 1/2] riscv: kdump: Implement crashkernel=X,[high,low]

[chenjiahao (C)]

On 2023/3/31 7:32, Baoquan He wrote:
> On 03/30/23 at 09:40pm, chenjiahao (C) wrote:
> ......
> > Agreed, I will clean this up later in next version.
> > > > +		if (ret || !crash_size)
> > > > +			return;
> > > > +
> > > > +		/*
> > > > +		 * crashkernel=Y,low is valid only when crashkernel=X,high
> > > > +		 * is passed and high memory is reserved successful.
> > > > +		 */
> > > > +		ret = parse_crashkernel_low(boot_command_line, 0, &crash_low_size, &crash_base);
> > > > +		if (ret == -ENOENT)
> > > > +			crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
> > > > +		else if (ret)
> > > > +			return;
> > > > +
> > > > +		search_start = dma32_phys_limit;
> > > > +	} else if (ret || !crash_size) {
> > > > +		/* Invalid argument value specified */
> > > >    		return;
> > > > +	}
> > > >    	crash_size = PAGE_ALIGN(crash_size);
> > > > @@ -1201,16 +1246,26 @@ static void __init reserve_crashkernel(void)
> > > >    	 */
> > > >    	crash_base = memblock_phys_alloc_range(crash_size, PMD_SIZE,
> > > >    					       search_start,
> > > > -					       min(search_end, (unsigned long) SZ_4G));
> > > > +					       min(search_end, (unsigned long)dma32_phys_limit));
> > > >    	if (crash_base == 0) {
> > > The above conditional check isn't right. If crashkernel=size@offset
> > > specified, the reservation failure won't trigger retry. This seems to be
> > > originally introduced by old commit, while this need be fixed firstly.
> > Just a little curious about the rule to cope with this specific case. If
> > "crashkernel=size@offset" was passed
> >
> > but reserve failed, should try again to allocate in high memory, regardless
> > the specified size@offset,
> >
> > or just throw a warning and return? Since I noticed the current logic here
> > on Arm64 is to check if !fixed_base first
> Yeah, we need mark the "crashkernel=size@offset" case and avoid to
> retry. Because you won't succeed if  memblock has already failed to
> reserve an unavailable memory region, retry is meaningless. This has
> been done in x86, arm64.

Make sense, thanks.

Actually, in my previous tests, the result in this case is the same
as expectation, i.e. when allocating "crashkernel=size@offset" failed
on low memory, it would retry but return on failure. Since the
search_end is assigned with offset + size, which is lower than DMA32
limit, the second allocation is definitely invalid.

But for sure, to make the code easy to read and eradicate other
possible corner cases, I will check if !fixed_base first on retry.

>