[PATCH v22 1/8] arm64: kdump: reserve memory for crash dump kernel

[Mark Rutland]

On Tue, Jul 19, 2016 at 08:48:57AM -0400, Mark Salter wrote:
> On Tue, 2016-07-19 at 18:41 +0800, Dennis Chen wrote:
> > On Tue, Jul 19, 2016 at 07:28:16PM +0900, AKASHI Takahiro wrote:
> > > On Tue, Jul 19, 2016 at 05:39:07PM +0800, Dennis Chen wrote:
> > > > On Tue, Jul 12, 2016 at 02:05:07PM +0900, AKASHI Takahiro wrote:
> > > > > +/*
> > > > > + * reserve_crashkernel() - reserves memory for crash kernel
> > > > > + *
> > > > > + * This function reserves memory area given in "crashkernel=" kernel command
> > > > > + * line parameter. The memory reserved is used by dump capture kernel when
> > > > > + * primary kernel is crashing.
> > > > > + */
> > > > > +static void __init reserve_crashkernel(void)
> > > > > +{
> > > > > +     int ret;
> > > > > +
> > > > > +     ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),
> > > > > +                             &crash_size, &crash_base);
> > > > > +     /* no crashkernel= or invalid value specified */
> > > > > +     if (ret || !crash_size)
> > > > > +             return;
> > > > > +
> > > > > +     if (crash_base == 0) {
> > > > > +             /* Current arm64 boot protocol requires 2MB alignment */
> > > > > +             crash_base = memblock_find_in_range(0,
> > > > > +                             MEMBLOCK_ALLOC_ACCESSIBLE, crash_size, SZ_2M);
> > > > > +             if (crash_base == 0) {
> > > > > +                     pr_warn("Unable to allocate crashkernel (size:%llx)\n",
> > > > > +                             crash_size);
> > > > > +                     return;
> > > > > +             }
> > > > > +             memblock_reserve(crash_base, crash_size);
> > > > > 
> > > > I am not pretty sure the context here, but
> > > > can we use below code piece instead of the above lines?
> > > >         if (crash_base == 0)
> > > >                 memblock_alloc(crash_size, SZ_2M);
> > > Either would be fine here.
> > > 
> > Hello AKASHI, maybe you can succeed to find the base with memblock_find_in_range(), 
> > but that doesn't mean you will also succeed to reserve them with memblock_reserve followed.
> 
> We avoid memblock_alloc() here because it panics on failure. This could happen
> if user asks for an unusually large crashkernel size. Better to print a message
> and keep booting. Checking the return value of memblock_reserve() seems like a
> good thing to do though.

Another option would be to add a memblock_try_alloc() function to the
memblock API, which in case of failure returns 0 rather than triggering
a panic(). We'd still have to check the return value, but all the
memblock manipulation would be in one place.

It looks like adding that is fairly simple:

phys_addr_t __init memblock_try_alloc(phys_addr_t size, phys_addr_t align)
{
	return __memblock_alloc_base(size, align, MEMBLOCK_ALLOC_ACCESSIBLE);
}

Thanks,
Mark.