[PATCH 4.9 14/30] staging: android: ion: Switch to pr_warn_once in ion_buffer_destroy

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Laura Abbott <labbott@redhat.com>

commit 45ad559a29629cb1c64ee636563c69b71524f077 upstream.

Syzbot reported yet another warning with Ion:

WARNING: CPU: 0 PID: 1467 at drivers/staging/android/ion/ion.c:122
ion_buffer_destroy+0xd4/0x190 drivers/staging/android/ion/ion.c:122
Kernel panic - not syncing: panic_on_warn set ...

This is catching that a buffer was freed with an existing kernel mapping
still present. This can be easily be triggered from userspace by calling
DMA_BUF_SYNC_START without calling DMA_BUF_SYNC_END. Switch to a single
pr_warn_once to indicate the error without being disruptive.

Reported-by: syzbot+cd8bcd40cb049efa2770@syzkaller.appspotmail.com
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Laura Abbott <labbott@redhat.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/staging/android/ion/ion.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/drivers/staging/android/ion/ion.c
+++ b/drivers/staging/android/ion/ion.c
@@ -192,8 +192,11 @@ err2:
 
 void ion_buffer_destroy(struct ion_buffer *buffer)
 {
-	if (WARN_ON(buffer->kmap_cnt > 0))
+	if (buffer->kmap_cnt > 0) {
+		pr_warn_once("%s: buffer still mapped in the kernel\n",
+			     __func__);
 		buffer->heap->ops->unmap_kernel(buffer->heap, buffer);
+	}
 	buffer->heap->ops->free(buffer);
 	vfree(buffer->pages);
 	kfree(buffer);