Re: [PATCH] memblock: Add error message when memblock_can_resize is not ready

[Song Shuai]

Sorry for not replying to you in time

在 2023/6/15 00:07, Mike Rapoport 写道:
> Hi,
>
> On Wed, Jun 14, 2023 at 09:17:46PM +0800, Song Shuai wrote:
> > The memblock APIs are always correct, thus the callers usually don't
> > handle the return code. But the failure caused by unready memblock_can_resize
> > is hard to recognize without the return code. Like this piece of log:
>
> Please make it clear that failure is in memblock_double_array(), e.g.

Having numerous memblock reservations at early boot where 
memblock_can_resize is unset
may exhaust the INIT_MEMBLOCK_REGIONS sized memblock.reserved regions 
and try to
double the region array via memblock_double_array() which fails and 
returns -1 to the caller.

You can find the numerous memblock reservations reported by this commit
24cc61d8cb5a ("arm64: memblock: don't permit memblock resizing until 
linear mapping is up").
And the similar test sense can be simulated by a constructed dtb with 
numerous discrete
/memreserve/ or /reserved-memory regions.

> But when memblock_double_array() is called before memblock_can_resize
> is true, it is hard to understand the actual reason for the failure.
>
> > ```
> > [    0.000000] memblock_phys_alloc_range: 4096 bytes align=0x1000 from=0x0000000000000000 max_addr=0x0000000000000000 alloc_pmd_fixmap+0x14/0x1c
> > [    0.000000] memblock_reserve: [0x000000017ffff000-0x000000017fffffff] memblock_alloc_range_nid+0xb8/0x128
> > [    0.000000] Oops - store (or AMO) access fault [#1]
> > ```
> >
> > So add an error message for this kind of failure:
> >
> > ```
> > [    0.000000] memblock_phys_alloc_range: 4096 bytes align=0x1000 from=0x0000000000000000 max_addr=0x0000000000000000 alloc_pmd_fixmap+0x14/0x1c
> > [    0.000000] memblock_reserve: [0x000000017ffff000-0x000000017fffffff] memblock_alloc_range_nid+0xb8/0x128
> > [    0.000000] memblock: Can't double reserved array for area start 0x000000017ffff000 size 4096
> > [    0.000000] Oops - store (or AMO) access fault [#1]
> > ```
> >
> > Signed-off-by: Song Shuai <songshuaishuai@xxxxxxxxxxx>
> > ---
> >   mm/memblock.c | 5 ++++-
> >   1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/memblock.c b/mm/memblock.c
> > index 3feafea06ab2..ab952a164f62 100644
> > --- a/mm/memblock.c
> > +++ b/mm/memblock.c
> > @@ -418,8 +418,11 @@ static int __init_memblock memblock_double_array(struct memblock_type *type,
> >   	/* We don't allow resizing until we know about the reserved regions
> >   	 * of memory that aren't suitable for allocation
> >   	 */
> > -	if (!memblock_can_resize)
> > +	if (!memblock_can_resize) {
> > +		pr_err("memblock: Can't double %s array for area start %pa size %ld\n",
> > +			type->name, &new_area_start, (unsigned long)new_area_size);
>
> Most of the time memblock uses %llu and cast to u64 to print size, please
> make this consistent.
I will fix it in next version if the above description is ok for you.
> >   		return -1;
> > +	}
> >   
> >   	/* Calculate new doubled size */
> >   	old_size = type->max * sizeof(struct memblock_region);
> > --
> > 2.20.1

--
Thanks
Song Shuai