Re: kmemleak panic

[Robin Murphy]

On 21/01/2019 15:42, Rob Herring wrote:
> +Mike Rapoport
>
> On Mon, Jan 21, 2019 at 8:37 AM Catalin Marinas <catalin.marinas@xxxxxxx> wrote:
> > On Mon, Jan 21, 2019 at 07:35:11AM -0600, Rob Herring wrote:
> > > On Mon, Jan 21, 2019 at 6:19 AM Robin Murphy <robin.murphy@xxxxxxx> wrote:
> > > > On 21/01/2019 11:57, Marc Gonzalez wrote:
> > > > [...]
> > > > > # echo dump=0xffffffc021e00000 > /sys/kernel/debug/kmemleak
> > > > > kmemleak: Object 0xffffffc021e00000 (size 2097152):
> > > > > kmemleak:   comm "swapper/0", pid 0, jiffies 4294892296
> > > > > kmemleak:   min_count = 0
> > > > > kmemleak:   count = 0
> > > > > kmemleak:   flags = 0x1
> > > > > kmemleak:   checksum = 0
> > > > > kmemleak:   backtrace:
> > > > >        kmemleak_alloc_phys+0x48/0x60
> > > > >        memblock_alloc_range_nid+0x8c/0xa4
> > > > >        memblock_alloc_base_nid+0x4c/0x60
> > > > >        __memblock_alloc_base+0x3c/0x4c
> > > > >        early_init_dt_alloc_reserved_memory_arch+0x54/0xa4
> > > > >        fdt_init_reserved_mem+0x308/0x3ec
> > > > >        early_init_fdt_scan_reserved_mem+0x88/0xb0
> > > > >        arm64_memblock_init+0x1dc/0x254
> > > > >        setup_arch+0x1c8/0x4ec
> > > > >        start_kernel+0x84/0x44c
> > > > >        0xffffffffffffffff
> > > >
> > > > OK, so via the __va(phys) call in kmemleak_alloc_phys(), you end up with
> > > > the linear map address of a no-map reservation, which unsurprisingly
> > > > turns out not to be mapped. Is there a way to tell kmemleak that it
> > > > can't scan within a particular object?
> > >
> > > There was this patch posted[1]. I never got a reply, so it hasn't been applied.
> > >
> > > https://patchwork.ozlabs.org/patch/995367/
> >
> > Thanks Rob, I wasn't aware of this patch (or I just missed it at the
> > time).
> >
> > I wonder whether kmemleak should simply remove ranges passed to
> > memblock_remove(), or at least mark them as no-scan.
>
> Seems reasonable to me, but of course that impacts a lot of other
> cases. Maybe Mike R has some thoughts?

In particular, might that risk crippling kmemleak on EFI arm64 EFI, 
where we memblock_remove() the entire physical address space (but then 
rebuild the memblock list from scratch)?

FWIW, from the reserved-memory angle I think that patch looks reasonable 
as-is (modulo perhaps a kmemleak_no_scan_phys() wrapper for API 
symmetry). MEMBLOCK_NOMAP is already a massive pain in the bum and I'd 
really rather not introduce any more usage of it if at all possible.

Robin.