linux-kernel - Re: [PATCH] dma-pool: Do not allocate pool memory from CMA

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Date:   Tue, 21 Jul 2020 10:39:49 +0200
From:   Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
To:     Amit Pundir <amit.pundir@...aro.org>
Cc:     Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        David Rientjes <rientjes@...gle.com>,
        linux-rpi-kernel@...ts.infradead.org, jeremy.linton@....com,
        iommu@...ts.linux-foundation.org,
        lkml <linux-kernel@...r.kernel.org>,
        John Stultz <john.stultz@...aro.org>,
        Sumit Semwal <sumit.semwal@...aro.org>
Subject: Re: [PATCH] dma-pool: Do not allocate pool memory from CMA

Hi Amit,

On Tue, 2020-07-21 at 12:51 +0530, Amit Pundir wrote:
> On Wed, 8 Jul 2020 at 22:43, Nicolas Saenz Julienne
> <nsaenzjulienne@...e.de> wrote:
> > There is no guarantee to CMA's placement, so allocating a zone
> > specific
> > atomic pool from CMA might return memory from a completely
> > different
> > memory zone. So stop using it.
> > 
> > Fixes: c84dc6e68a1d ("dma-pool: add additional coherent pools to
> > map to gfp mask")
> 
> Hi Nicolas,
> 
> I see a boot regression with this commit d9765e41d8e9 "dma-pool:
> Do not allocate pool memory from CMA" on my Xiaomi Poco F1
> (Qcom sdm845) phone running v5.8-rc6. I can't boot past the
> bootloader splash screen with this patch.
> 
> Phone boots fine if I revert this patch. I carry only one out of tree
> dts patch https://lkml.org/lkml/2020/6/25/52. And since this is a
> stock
> phone, I don't have access to serial/dmesg logs until I boot to AOSP
> (adb) shell.
> 
> Any thoughts as to what might be going wrong here? I'd be happy to
> help debug things. For what it's worth, I don't see this regression
> on
> other two sdm845 devices (db845c and Pixel 3) I tested on.

Can you provide a boot log (even if without my patch) and the device-
tree files? It'd help a lot figuring things out.

Regards,
Nicolas

> Regards,
> Amit Pundir
> 
> > Reported-by: Jeremy Linton <jeremy.linton@....com>
> > Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
> > ---
> > 
> > An more costly alternative would be adding an option to
> > dma_alloc_from_contiguous() so it fails when the allocation doesn't
> > fall
> > in a specific zone.
> > 
> >  kernel/dma/pool.c | 11 ++---------
> >  1 file changed, 2 insertions(+), 9 deletions(-)
> > 
> > diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
> > index 8cfa01243ed2..4bc1c46ae6ef 100644
> > --- a/kernel/dma/pool.c
> > +++ b/kernel/dma/pool.c
> > @@ -6,7 +6,6 @@
> >  #include <linux/debugfs.h>
> >  #include <linux/dma-direct.h>
> >  #include <linux/dma-noncoherent.h>
> > -#include <linux/dma-contiguous.h>
> >  #include <linux/init.h>
> >  #include <linux/genalloc.h>
> >  #include <linux/set_memory.h>
> > @@ -69,12 +68,7 @@ static int atomic_pool_expand(struct gen_pool
> > *pool, size_t pool_size,
> > 
> >         do {
> >                 pool_size = 1 << (PAGE_SHIFT + order);
> > -
> > -               if (dev_get_cma_area(NULL))
> > -                       page = dma_alloc_from_contiguous(NULL, 1 <<
> > order,
> > -                                                        order,
> > false);
> > -               else
> > -                       page = alloc_pages(gfp, order);
> > +               page = alloc_pages(gfp, order);
> >         } while (!page && order-- > 0);
> >         if (!page)
> >                 goto out;
> > @@ -118,8 +112,7 @@ static int atomic_pool_expand(struct gen_pool
> > *pool, size_t pool_size,
> >         dma_common_free_remap(addr, pool_size);
> >  #endif
> >  free_page: __maybe_unused
> > -       if (!dma_release_from_contiguous(NULL, page, 1 << order))
> > -               __free_pages(page, order);
> > +       __free_pages(page, order);
> >  out:
> >         return ret;
> >  }
> > --
> > 2.27.0
> >