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

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Message-ID: <DB7PR04MB449005901376F086215EC79A88600@DB7PR04MB4490.eurprd04.prod.outlook.com>
Date:   Fri, 15 Feb 2019 01:30:40 +0000
From:   Peng Fan <peng.fan@....com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     "labbott@...hat.com" <labbott@...hat.com>,
        "mhocko@...e.com" <mhocko@...e.com>,
        "vbabka@...e.cz" <vbabka@...e.cz>,
        "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>,
        Mike Rapoport <rppt@...ux.ibm.com>
Subject: RE: [PATCH] mm/cma: cma_declare_contiguous: correct err handling

Hi Andrew

> -----Original Message-----
> From: Andrew Morton [mailto:akpm@...ux-foundation.org]
> Sent: 2019年2月15日 4:38
> To: Peng Fan <peng.fan@....com>
> Cc: labbott@...hat.com; mhocko@...e.com; vbabka@...e.cz;
> 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; Mike Rapoport <rppt@...ux.ibm.com>
> Subject: Re: [PATCH] mm/cma: cma_declare_contiguous: correct err handling
> 
> 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'.

My code base is 5.0.0-rc6, in mm/cma.c
313         /* Reserve memory */
314         if (fixed) {
315                 if (memblock_is_region_reserved(base, size) ||
316                     memblock_reserve(base, size) < 0) {
317                         ret = -EBUSY;
318                         goto err;
319                 }
320         } else {

When fixed is true, memblock_is_region_reserved will check whether the [base, base + size)
is reserved, if reserved, return -EBUSY, if not reserved, it will call memblock_reserve,
if memblock_reserve fail, it will return -EBUSY.

When fixed is false, after memblock_alloc_range, there is one line code `base = addr;`.

Thanks,
Peng.