Re: [PATCH] mm: kmemleak: Ignore kmemleak scanning on CMA regions

[Catalin Marinas]

On Sun, Nov 28, 2021 at 09:50:53AM +0800, Calvin Zhang wrote:
> On Sat, Nov 27, 2021 at 04:07:18PM -0800, Andrew Morton wrote:
> >On Fri, 26 Nov 2021 10:47:11 +0800 Calvin Zhang <calvinzhang.cool@xxxxxxxxx> wrote:
> >> Just like this:
> >> commit 620951e27457 ("mm/cma: make kmemleak ignore CMA regions").
> >> 
> >> Add kmemleak_ignore_phys() for CMA created from of reserved node.
[...]
> >The 620951e27457 changelog says "Without this, the kernel crashes...". 
> >Does your patch also fix a crash?  If so under what circumstances and
> >should we backport this fix into -stable kernels?
> 
> No crash occurred. 620951e27457 avoids crashes caused by accessing
> highmem and it was fixed later. Now kmemleak_alloc_phys() and
> kmemleak_ignore_phys() skip highmem. This patch is based on the
> point that CMA regions don't contain pointers to other kmemleak
> objects, and ignores CMA regions from reserved memory as what
> 620951e27457 did.

Note that kmemleak_ignore() only works if there was a prior
kmemleak_alloc() on that address range. With the previous commit we get
this via the memblock_alloc_range() but I fail to see one on the
rmem_cma_setup() path.

-- 
Catalin