Re: [RESEND][PATCH 2/3] dma-buf: heaps: Add a WARN_ON should the vmap_cnt go negative
On Fri, Jan 22, 2021 at 2:21 PM Suren Baghdasaryan wrote: > On Thu, Jan 21, 2021 at 11:56 PM Sumit Semwal wrote: > > On Wed, 20 Jan 2021 at 02:15, John Stultz wrote: > > > > > > We shouldn't vunmap more then we vmap, but if we do, make > > > sure we complain loudly. > > > > I was checking the general usage of vunmap in the kernel, and I > > couldn't find many instances where we need to WARN_ON for the vunmap > > count more than vmap count. Is there a specific need for this in the heaps? > > Hi Sumit, > My worry was that buffer->vmap_cnt could silently go negative. But if > this warning is not consistent with other places we do refcounted > vmap/vunmap then feel free to ignore my suggestion. > Yea, My sense is that it didn't seem like it would hurt, and if the warning happened to be tripped, it would be good to catch. However, if you are skeptical, feel free to drop that patch from this series for now (it shouldn't impact the following patches). thanks -john
Re: [RESEND][PATCH 2/3] dma-buf: heaps: Add a WARN_ON should the vmap_cnt go negative
On Thu, Jan 21, 2021 at 11:56 PM Sumit Semwal wrote:
>
> Hi John, Suren,
>
>
> On Wed, 20 Jan 2021 at 02:15, John Stultz wrote:
> >
> > We shouldn't vunmap more then we vmap, but if we do, make
> > sure we complain loudly.
>
> I was checking the general usage of vunmap in the kernel, and I
> couldn't find many instances where we need to WARN_ON for the vunmap
> count more than vmap count. Is there a specific need for this in the heaps?
Hi Sumit,
My worry was that buffer->vmap_cnt could silently go negative. But if
this warning is not consistent with other places we do refcounted
vmap/vunmap then feel free to ignore my suggestion.
Thanks!
>
> Best,
> Sumit.
> >
> > Cc: Sumit Semwal
> > Cc: Liam Mark
> > Cc: Laura Abbott
> > Cc: Brian Starkey
> > Cc: Hridya Valsaraju
> > Cc: Suren Baghdasaryan
> > Cc: Sandeep Patil
> > Cc: Daniel Mentz
> > Cc: Chris Goldsworthy
> > Cc: Ørjan Eide
> > Cc: Robin Murphy
> > Cc: Ezequiel Garcia
> > Cc: Simon Ser
> > Cc: James Jones
> > Cc: linux-me...@vger.kernel.org
> > Cc: dri-de...@lists.freedesktop.org
> > Suggested-by: Suren Baghdasaryan
> > Signed-off-by: John Stultz
> > ---
> > drivers/dma-buf/heaps/cma_heap.c| 1 +
> > drivers/dma-buf/heaps/system_heap.c | 1 +
> > 2 files changed, 2 insertions(+)
> >
> > diff --git a/drivers/dma-buf/heaps/cma_heap.c
> > b/drivers/dma-buf/heaps/cma_heap.c
> > index 364fc2f3e499..0c76cbc3fb11 100644
> > --- a/drivers/dma-buf/heaps/cma_heap.c
> > +++ b/drivers/dma-buf/heaps/cma_heap.c
> > @@ -232,6 +232,7 @@ static void cma_heap_vunmap(struct dma_buf *dmabuf,
> > struct dma_buf_map *map)
> > struct cma_heap_buffer *buffer = dmabuf->priv;
> >
> > mutex_lock(>lock);
> > + WARN_ON(buffer->vmap_cnt == 0);
> > if (!--buffer->vmap_cnt) {
> > vunmap(buffer->vaddr);
> > buffer->vaddr = NULL;
> > diff --git a/drivers/dma-buf/heaps/system_heap.c
> > b/drivers/dma-buf/heaps/system_heap.c
> > index 405351aad2a8..2321c91891f6 100644
> > --- a/drivers/dma-buf/heaps/system_heap.c
> > +++ b/drivers/dma-buf/heaps/system_heap.c
> > @@ -273,6 +273,7 @@ static void system_heap_vunmap(struct dma_buf *dmabuf,
> > struct dma_buf_map *map)
> > struct system_heap_buffer *buffer = dmabuf->priv;
> >
> > mutex_lock(>lock);
> > + WARN_ON(buffer->vmap_cnt == 0);
> > if (!--buffer->vmap_cnt) {
> > vunmap(buffer->vaddr);
> > buffer->vaddr = NULL;
> > --
> > 2.17.1
> >
Re: [RESEND][PATCH 2/3] dma-buf: heaps: Add a WARN_ON should the vmap_cnt go negative
Hi John, Suren,
On Wed, 20 Jan 2021 at 02:15, John Stultz wrote:
>
> We shouldn't vunmap more then we vmap, but if we do, make
> sure we complain loudly.
I was checking the general usage of vunmap in the kernel, and I
couldn't find many instances where we need to WARN_ON for the vunmap
count more than vmap count. Is there a specific need for this in the heaps?
Best,
Sumit.
>
> Cc: Sumit Semwal
> Cc: Liam Mark
> Cc: Laura Abbott
> Cc: Brian Starkey
> Cc: Hridya Valsaraju
> Cc: Suren Baghdasaryan
> Cc: Sandeep Patil
> Cc: Daniel Mentz
> Cc: Chris Goldsworthy
> Cc: Ørjan Eide
> Cc: Robin Murphy
> Cc: Ezequiel Garcia
> Cc: Simon Ser
> Cc: James Jones
> Cc: linux-me...@vger.kernel.org
> Cc: dri-de...@lists.freedesktop.org
> Suggested-by: Suren Baghdasaryan
> Signed-off-by: John Stultz
> ---
> drivers/dma-buf/heaps/cma_heap.c| 1 +
> drivers/dma-buf/heaps/system_heap.c | 1 +
> 2 files changed, 2 insertions(+)
>
> diff --git a/drivers/dma-buf/heaps/cma_heap.c
> b/drivers/dma-buf/heaps/cma_heap.c
> index 364fc2f3e499..0c76cbc3fb11 100644
> --- a/drivers/dma-buf/heaps/cma_heap.c
> +++ b/drivers/dma-buf/heaps/cma_heap.c
> @@ -232,6 +232,7 @@ static void cma_heap_vunmap(struct dma_buf *dmabuf,
> struct dma_buf_map *map)
> struct cma_heap_buffer *buffer = dmabuf->priv;
>
> mutex_lock(>lock);
> + WARN_ON(buffer->vmap_cnt == 0);
> if (!--buffer->vmap_cnt) {
> vunmap(buffer->vaddr);
> buffer->vaddr = NULL;
> diff --git a/drivers/dma-buf/heaps/system_heap.c
> b/drivers/dma-buf/heaps/system_heap.c
> index 405351aad2a8..2321c91891f6 100644
> --- a/drivers/dma-buf/heaps/system_heap.c
> +++ b/drivers/dma-buf/heaps/system_heap.c
> @@ -273,6 +273,7 @@ static void system_heap_vunmap(struct dma_buf *dmabuf,
> struct dma_buf_map *map)
> struct system_heap_buffer *buffer = dmabuf->priv;
>
> mutex_lock(>lock);
> + WARN_ON(buffer->vmap_cnt == 0);
> if (!--buffer->vmap_cnt) {
> vunmap(buffer->vaddr);
> buffer->vaddr = NULL;
> --
> 2.17.1
>
