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

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Message-Id: <20190226111158.GF11981@rapoport-lnx>
Date:   Tue, 26 Feb 2019 13:11:58 +0200
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     Peng Fan <peng.fan@....com>
Cc:     Vlastimil Babka <vbabka@...e.cz>,
        Catalin Marinas <catalin.marinas@....com>,
        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>
Subject: Re: [PATCH] mm/cma: cma_declare_contiguous: correct err handling

On Fri, Feb 22, 2019 at 12:55:41PM +0000, Peng Fan wrote:
> 
> 
> > -----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?
 
I'd suggest to wait for Catalin to review it.

I think it's also worth making the changelog more elaborate and include the
details we've discussed in this thread.

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

-- 
Sincerely yours,
Mike.