Re: [PATCH v2 1/4] dma-buf: Add dma_buf_try_get()
Am 06.09.22 um 18:44 schrieb Jason Gunthorpe: On Thu, Sep 01, 2022 at 09:55:08AM +0200, Christian König wrote: Am 01.09.22 um 01:12 schrieb Jason Gunthorpe: Used to increment the refcount of the dma buf's struct file, only if the refcount is not zero. Useful to allow the struct file's lifetime to control the lifetime of the dmabuf while still letting the driver to keep track of created dmabufs. Signed-off-by: Jason Gunthorpe --- include/linux/dma-buf.h | 13 + 1 file changed, 13 insertions(+) diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h index 71731796c8c3a8..a35f1554f2fb36 100644 --- a/include/linux/dma-buf.h +++ b/include/linux/dma-buf.h @@ -618,6 +618,19 @@ int dma_buf_fd(struct dma_buf *dmabuf, int flags); struct dma_buf *dma_buf_get(int fd); void dma_buf_put(struct dma_buf *dmabuf); +/** + * dma_buf_try_get - try to get a reference on a dmabuf + * @dmabuf - the dmabuf to get + * + * Returns true if a reference was successfully obtained. The caller must + * interlock with the dmabuf's release function in some way, such as RCU, to + * ensure that this is not called on freed memory. I still have a bad feeling about this, but I also see that we can only choose between evils here. Could you just call get_file_rcu() from the exporter with a comment explaining why this works instead? I guess, are you sure? It seems very hacky. Yes, it's still better than exposing a dma_buf_try_get() interface to everyone. Keep in mind that those functions here are mostly supposed to be used by the importer and not the exporter. Christian. Jason
Re: [PATCH v2 1/4] dma-buf: Add dma_buf_try_get()
On Thu, Sep 01, 2022 at 09:55:08AM +0200, Christian König wrote: > Am 01.09.22 um 01:12 schrieb Jason Gunthorpe: > > Used to increment the refcount of the dma buf's struct file, only if the > > refcount is not zero. Useful to allow the struct file's lifetime to > > control the lifetime of the dmabuf while still letting the driver to keep > > track of created dmabufs. > > > > Signed-off-by: Jason Gunthorpe > > --- > > include/linux/dma-buf.h | 13 + > > 1 file changed, 13 insertions(+) > > > > diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h > > index 71731796c8c3a8..a35f1554f2fb36 100644 > > --- a/include/linux/dma-buf.h > > +++ b/include/linux/dma-buf.h > > @@ -618,6 +618,19 @@ int dma_buf_fd(struct dma_buf *dmabuf, int flags); > > struct dma_buf *dma_buf_get(int fd); > > void dma_buf_put(struct dma_buf *dmabuf); > > +/** > > + * dma_buf_try_get - try to get a reference on a dmabuf > > + * @dmabuf - the dmabuf to get > > + * > > + * Returns true if a reference was successfully obtained. The caller must > > + * interlock with the dmabuf's release function in some way, such as RCU, > > to > > + * ensure that this is not called on freed memory. > > I still have a bad feeling about this, but I also see that we can only > choose between evils here. > > Could you just call get_file_rcu() from the exporter with a comment > explaining why this works instead? I guess, are you sure? It seems very hacky. Jason
Re: [PATCH v2 1/4] dma-buf: Add dma_buf_try_get()
Am 01.09.22 um 01:12 schrieb Jason Gunthorpe:
Used to increment the refcount of the dma buf's struct file, only if the
refcount is not zero. Useful to allow the struct file's lifetime to
control the lifetime of the dmabuf while still letting the driver to keep
track of created dmabufs.
Signed-off-by: Jason Gunthorpe
---
include/linux/dma-buf.h | 13 +
1 file changed, 13 insertions(+)
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index 71731796c8c3a8..a35f1554f2fb36 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -618,6 +618,19 @@ int dma_buf_fd(struct dma_buf *dmabuf, int flags);
struct dma_buf *dma_buf_get(int fd);
void dma_buf_put(struct dma_buf *dmabuf);
+/**
+ * dma_buf_try_get - try to get a reference on a dmabuf
+ * @dmabuf - the dmabuf to get
+ *
+ * Returns true if a reference was successfully obtained. The caller must
+ * interlock with the dmabuf's release function in some way, such as RCU, to
+ * ensure that this is not called on freed memory.
I still have a bad feeling about this, but I also see that we can only
choose between evils here.
Could you just call get_file_rcu() from the exporter with a comment
explaining why this works instead?
That would at least not give importers the opportunity to abuse this.
Thanks,
Christian.
+ */
+static inline bool dma_buf_try_get(struct dma_buf *dmabuf)
+{
+ return get_file_rcu(dmabuf->file);
+}
+
struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *,
enum dma_data_direction);
void dma_buf_unmap_attachment(struct dma_buf_attachment *, struct sg_table *,
[PATCH v2 1/4] dma-buf: Add dma_buf_try_get()
Used to increment the refcount of the dma buf's struct file, only if the
refcount is not zero. Useful to allow the struct file's lifetime to
control the lifetime of the dmabuf while still letting the driver to keep
track of created dmabufs.
Signed-off-by: Jason Gunthorpe
---
include/linux/dma-buf.h | 13 +
1 file changed, 13 insertions(+)
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index 71731796c8c3a8..a35f1554f2fb36 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -618,6 +618,19 @@ int dma_buf_fd(struct dma_buf *dmabuf, int flags);
struct dma_buf *dma_buf_get(int fd);
void dma_buf_put(struct dma_buf *dmabuf);
+/**
+ * dma_buf_try_get - try to get a reference on a dmabuf
+ * @dmabuf - the dmabuf to get
+ *
+ * Returns true if a reference was successfully obtained. The caller must
+ * interlock with the dmabuf's release function in some way, such as RCU, to
+ * ensure that this is not called on freed memory.
+ */
+static inline bool dma_buf_try_get(struct dma_buf *dmabuf)
+{
+ return get_file_rcu(dmabuf->file);
+}
+
struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *,
enum dma_data_direction);
void dma_buf_unmap_attachment(struct dma_buf_attachment *, struct sg_table *,
--
2.37.2
