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SubjectRe: [PATCH] mm/cma: cma_declare_contiguous: correct err handling
On Tue, Feb 19, 2019 at 05:55:33PM +0100, Vlastimil Babka wrote:
> On 2/14/19 9:38 PM, Andrew Morton wrote:
> > On Thu, 14 Feb 2019 12:45:51 +0000 Peng Fan <peng.fan@nxp.com> wrote:
> >
> >> In case cma_init_reserved_mem failed, need to free the memblock allocated
> >> by memblock_reserve or memblock_alloc_range.
> >>
> >> ...
> >>
> >> --- a/mm/cma.c
> >> +++ b/mm/cma.c
> >> @@ -353,12 +353,14 @@ int __init cma_declare_contiguous(phys_addr_t base,
> >>
> >> ret = cma_init_reserved_mem(base, size, order_per_bit, name, res_cma);
> >> if (ret)
> >> - goto err;
> >> + goto free_mem;
> >>
> >> pr_info("Reserved %ld MiB at %pa\n", (unsigned long)size / SZ_1M,
> >> &base);
> >> return 0;
> >>
> >> +free_mem:
> >> + memblock_free(base, size);
> >> err:
> >> pr_err("Failed to reserve %ld MiB\n", (unsigned long)size / SZ_1M);
> >> return ret;
> >
> > This doesn't look right to me. In the `fixed==true' case we didn't
> > actually allocate anything and in the `fixed==false' case, the
> > allocated memory is at `addr', not at `base'.
>
> I think it's ok as the fixed==true path has "memblock_reserve()", but
> better leave this to the memblock maintainer :)

As Peng Fan noted in the other e-mail, fixed==true has memblock_reserve()
and fixed==false resets base = addr, so this is Ok.

> There's also 'kmemleak_ignore_phys(addr)' which should probably be
> undone (or not called at all) in the failure case. But it seems to be
> missing from the fixed==true path?

Well, memblock and kmemleak interaction does not seem to have clear
semantics anyway. memblock_free() calls kmemleak_free_part_phys() which
does not seem to care about ignored objects.
As for the fixed==true path, memblock_reserve() does not register the area
with kmemleak, so there would be no object to free in memblock_free().
AFAIU, kmemleak simply ignores this.

Catalin, can you comment please?

--
Sincerely yours,
Mike.

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