linux-kernel - [PATCH v2] dma-buf: remove restriction of IOCTL:DMA_BUF_SET

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Date:   Sat, 9 Oct 2021 13:55:04 +0800
From:   <guangming.cao@...iatek.com>
To:     <rdunlap@...radead.org>
CC:     <christian.koenig@....com>, <dri-devel@...ts.freedesktop.org>,
        <guangming.cao@...iatek.com>, <linaro-mm-sig@...ts.linaro.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-media@...r.kernel.org>,
        <linux-mediatek@...ts.infradead.org>, <matthias.bgg@...il.com>,
        <sumit.semwal@...aro.org>, <wsd_upstream@...iatek.com>,
        Guangming Cao <Guangming.Cao@...iatek.com>
Subject: [PATCH v2] dma-buf: remove restriction of IOCTL:DMA_BUF_SET_NAME

From: Guangming Cao <Guangming.Cao@...iatek.com>

If dma-buf don't want userspace users to touch the dmabuf buffer,
it seems we should add this restriction into dma_buf_ops.mmap,
not in this IOCTL:DMA_BUF_SET_NAME.

With this restriction, we can only know the kernel users of the dmabuf
by attachments.
However, for many userspace users, such as userpsace users of dma_heap,
they also need to mark the usage of dma-buf, and they don't care about
who attached to this dmabuf, and seems it's no meaning to be waiting for
IOCTL:DMA_BUF_SET_NAME rather than mmap.

Signed-off-by: Guangming Cao <Guangming.Cao@...iatek.com>
---
 drivers/dma-buf/dma-buf.c | 14 ++------------
 1 file changed, 2 insertions(+), 12 deletions(-)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 511fe0d217a0..db2f4efdec32 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -325,10 +325,8 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll)
 
 /**
  * dma_buf_set_name - Set a name to a specific dma_buf to track the usage.
- * The name of the dma-buf buffer can only be set when the dma-buf is not
- * attached to any devices. It could theoritically support changing the
- * name of the dma-buf if the same piece of memory is used for multiple
- * purpose between different devices.
+ * It could theoretically support changing the name of the dma-buf if the same
+ * piece of memory is used for multiple purpose between different devices.
  *
  * @dmabuf: [in]     dmabuf buffer that will be renamed.
  * @buf:    [in]     A piece of userspace memory that contains the name of
@@ -346,19 +344,11 @@ static long dma_buf_set_name(struct dma_buf *dmabuf, const char __user *buf)
 	if (IS_ERR(name))
 		return PTR_ERR(name);
 
-	dma_resv_lock(dmabuf->resv, NULL);
-	if (!list_empty(&dmabuf->attachments)) {
-		ret = -EBUSY;
-		kfree(name);
-		goto out_unlock;
-	}
 	spin_lock(&dmabuf->name_lock);
 	kfree(dmabuf->name);
 	dmabuf->name = name;
 	spin_unlock(&dmabuf->name_lock);
 
-out_unlock:
-	dma_resv_unlock(dmabuf->resv);
 	return ret;
 }
 
-- 
2.17.1