linux-kernel - Re: [PATCH] mm/cma: cma_declare_contiguous: correct err handling

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Date:   Tue, 19 Feb 2019 19:46:11 +0200
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Peng Fan <peng.fan@....com>,
        "labbott@...hat.com" <labbott@...hat.com>,
        "mhocko@...e.com" <mhocko@...e.com>,
        "iamjoonsoo.kim@....com" <iamjoonsoo.kim@....com>,
        "rppt@...ux.vnet.ibm.com" <rppt@...ux.vnet.ibm.com>,
        "m.szyprowski@...sung.com" <m.szyprowski@...sung.com>,
        "rdunlap@...radead.org" <rdunlap@...radead.org>,
        "andreyknvl@...gle.com" <andreyknvl@...gle.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "van.freenix@...il.com" <van.freenix@...il.com>,
        Catalin Marinas <catalin.marinas@....com>
Subject: Re: [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@....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.