[PATCH v4 5/6] dma-buf: Change locking policy for mmap()

Dmitry Osipenko
2023-05-29T22:46:24Z

Change locking policy of mmap() callback, making exporters responsible
for handling dma-buf reservation locking. Previous locking policy stated
that dma-buf is locked for both importers and exporters by the dma-buf
core, which caused a deadlock problem for DRM drivers in a case of
self-imported dma-bufs which required to take the lock from the DRM
exporter side.

Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
---
drivers/dma-buf/dma-buf.c | 17 +++--------------
1 file changed, 3 insertions(+), 14 deletions(-)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index aa4ea8530cb3..21916bba77d5 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -131,7 +131,6 @@ static struct file_system_type dma_buf_fs_type = {
static int dma_buf_mmap_internal(struct file *file, struct vm_area_struct *vma)
{
struct dma_buf *dmabuf;
- int ret;

if (!is_dma_buf_file(file))
return -EINVAL;
@@ -147,11 +146,7 @@ static int dma_buf_mmap_internal(struct file *file, struct vm_area_struct *vma)
dmabuf->size >> PAGE_SHIFT)
return -EINVAL;

- dma_resv_lock(dmabuf->resv, NULL);
- ret = dmabuf->ops->mmap(dmabuf, vma);
- dma_resv_unlock(dmabuf->resv);
-
- return ret;
+ return dmabuf->ops->mmap(dmabuf, vma);
}

static loff_t dma_buf_llseek(struct file *file, loff_t offset, int whence)
@@ -850,6 +845,7 @@ static struct sg_table * __map_dma_buf(struct dma_buf_attachment *attach,
* - &dma_buf_ops.release()
* - &dma_buf_ops.begin_cpu_access()
* - &dma_buf_ops.end_cpu_access()
+ * - &dma_buf_ops.mmap()
*
* 2. These &dma_buf_ops callbacks are invoked with locked dma-buf
* reservation and exporter can't take the lock:
@@ -858,7 +854,6 @@ static struct sg_table * __map_dma_buf(struct dma_buf_attachment *attach,
* - &dma_buf_ops.unpin()
* - &dma_buf_ops.map_dma_buf()
* - &dma_buf_ops.unmap_dma_buf()
- * - &dma_buf_ops.mmap()
* - &dma_buf_ops.vmap()
* - &dma_buf_ops.vunmap()
*
@@ -1463,8 +1458,6 @@ EXPORT_SYMBOL_NS_GPL(dma_buf_end_cpu_access, DMA_BUF);
int dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma,
unsigned long pgoff)
{
- int ret;
-
if (WARN_ON(!dmabuf || !vma))
return -EINVAL;

@@ -1485,11 +1478,7 @@ int dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma,
vma_set_file(vma, dmabuf->file);
vma->vm_pgoff = pgoff;

- dma_resv_lock(dmabuf->resv, NULL);
- ret = dmabuf->ops->mmap(dmabuf, vma);
- dma_resv_unlock(dmabuf->resv);
-
- return ret;
+ return dmabuf->ops->mmap(dmabuf, vma);
}
EXPORT_SYMBOL_NS_GPL(dma_buf_mmap, DMA_BUF);

--
2.40.1