linux-kernel - Re: [PATCH 1/4] mm: cma: Don't crash on allocation if CMA area can't be activated

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Message-ID: <CAL1ERfPiv6KG5Lim6F0w72z=j47D1KCWhukLc5T6jJPOHTP_mQ@mail.gmail.com>
Date:	Fri, 24 Oct 2014 10:02:49 +0800
From:	Weijie Yang <weijie.yang.kh@...il.com>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:	Michal Nazarewicz <mina86@...a86.com>,
	Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-sh@...r.kernel.org,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH 1/4] mm: cma: Don't crash on allocation if CMA area can't
 be activated

On Fri, Oct 24, 2014 at 7:42 AM, Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
> Hi Michal,
>
> On Thursday 23 October 2014 18:53:36 Michal Nazarewicz wrote:
>> On Thu, Oct 23 2014, Laurent Pinchart wrote:
>> > If activation of the CMA area fails its mutex won't be initialized,
>> > leading to an oops at allocation time when trying to lock the mutex. Fix
>> > this by failing allocation if the area hasn't been successfully actived,
>> > and detect that condition by moving the CMA bitmap allocation after page
>> > block reservation completion.
>> >
>> > Signed-off-by: Laurent Pinchart
>> > <laurent.pinchart+renesas@...asonboard.com>
>>
>> Cc: <stable@...r.kernel.org>  # v3.17
>> Acked-by: Michal Nazarewicz <mina86@...a86.com>

This patch is good, but how about add a active field in cma struct?
use cma->active to check whether cma is actived successfully.
I think it will make code more clear and readable.
Just my little opinion.


>> As a matter of fact, this is present in kernels earlier than 3.17 but in
>> the 3.17 the code has been moved from drivers/base/dma-contiguous.c to
>> mm/cma.c so this might require separate stable patch.  I can track this
>> and prepare a patch if you want.
>
> That could be done, but I'm not sure if it's really worth it. The bug only
> occurs when the CMA zone activation fails. I've ran into that case due to a
> bug introduced in v3.18-rc1, but this shouldn't be the case for older kernel
> versions.
>
> If you think the fix should be backported to stable kernels older than v3.17
> please feel free to cook up a patch.
>
>> > ---
>> >
>> >  mm/cma.c | 17 ++++++-----------
>> >  1 file changed, 6 insertions(+), 11 deletions(-)
>> >
>> > diff --git a/mm/cma.c b/mm/cma.c
>> > index 963bc4a..16c6650 100644
>> > --- a/mm/cma.c
>> > +++ b/mm/cma.c
>> > @@ -93,11 +93,6 @@ static int __init cma_activate_area(struct cma *cma)
>> >     unsigned i = cma->count >> pageblock_order;
>> >     struct zone *zone;
>> >
>> > -   cma->bitmap = kzalloc(bitmap_size, GFP_KERNEL);
>> > -
>> > -   if (!cma->bitmap)
>> > -           return -ENOMEM;
>> > -
>> >     WARN_ON_ONCE(!pfn_valid(pfn));
>> >     zone = page_zone(pfn_to_page(pfn));
>> >
>> > @@ -114,17 +109,17 @@ static int __init cma_activate_area(struct cma *cma)
>> >                      * to be in the same zone.
>> >                      */
>> >                     if (page_zone(pfn_to_page(pfn)) != zone)
>> > -                           goto err;
>> > +                           return -EINVAL;
>> >             }
>> >             init_cma_reserved_pageblock(pfn_to_page(base_pfn));
>> >     } while (--i);
>> >
>> > +   cma->bitmap = kzalloc(bitmap_size, GFP_KERNEL);
>> > +   if (!cma->bitmap)
>> > +           return -ENOMEM;
>> > +
>> >     mutex_init(&cma->lock);
>> >     return 0;
>> > -
>> > -err:
>> > -   kfree(cma->bitmap);
>> > -   return -EINVAL;
>> >  }
>> >
>> >  static int __init cma_init_reserved_areas(void)
>> > @@ -313,7 +308,7 @@ struct page *cma_alloc(struct cma *cma, int count,
>> > unsigned int align)
>> >     struct page *page = NULL;
>> >     int ret;
>> >
>> > -   if (!cma || !cma->count)
>> > +   if (!cma || !cma->count || !cma->bitmap)
>> >             return NULL;
>> >
>> >     pr_debug("%s(cma %p, count %d, align %d)\n", __func__, (void *)cma,
>
> --
> Regards,
>
> Laurent Pinchart
>
> --
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