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

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Date:   Fri, 22 Feb 2019 12:55:41 +0000
From:   Peng Fan <peng.fan@....com>
To:     Mike Rapoport <rppt@...ux.ibm.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Catalin Marinas <catalin.marinas@....com>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        "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



> -----Original Message-----
> From: Mike Rapoport [mailto:rppt@...ux.ibm.com]
> Sent: 2019年2月20日 1:46
> To: Vlastimil Babka <vbabka@...e.cz>
> Cc: Andrew Morton <akpm@...ux-foundation.org>; Peng Fan
> <peng.fan@....com>; labbott@...hat.com; mhocko@...e.com;
> iamjoonsoo.kim@....com; rppt@...ux.vnet.ibm.com;
> m.szyprowski@...sung.com; rdunlap@...radead.org;
> andreyknvl@...gle.com; linux-mm@...ck.org; linux-kernel@...r.kernel.org;
> 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.

I also go through the memblock_free flow, and agree with Mike
memblock_free 
    -> kmemleak_free_part_phys 
          -> kmemleak_free_part
                 |-> delete_object_part
                         |-> object = find_and_remove_object(ptr, 1);

memblock_reserve not register the area in kmemleak, so find_and_remove_object
will not be able to find a valid area and just return.

What should I do next with this patch?

Thanks,
Peng.

> 
> Catalin, can you comment please?
> 
> --
> Sincerely yours,
> Mike.