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authorMaxim Levitsky <maximlevitsky@gmail.com>2007-09-27 20:34:09 -0300
committerMauro Carvalho Chehab <mchehab@infradead.org>2007-10-10 00:02:58 -0300
commit9900132f3437e9373aa030cdb5bd2d5db15566e3 (patch)
treeb4b450daf16d1f502869dd472ae2bad85892daca /drivers/media/video/videobuf-dma-sg.c
parent851c0c96b2212f48fe51afc1589541b5eae3a544 (diff)
V4L/DVB (6268): V4L: Fix a lock inversion in generic videobuf code
videobuf_qbuf takes q->lock, and then calls q->ops->buf_prepare which by design in all drivers calls videobuf_iolock which calls videobuf_dma_init_user and this takes current->mm->mmap_sem on the other hand if user calls mumap from other thread, sys_munmap takes current->mm->mmap_sem and videobuf_vm_close takes q->lock Since this can occur only for V4L2_MEMORY_MMAP buffers, take current->mm->mmap_sem in qbuf, before q->lock, and don't take current->mm->mmap_sem videobuf_dma_init_user for those buffers Signed-off-by: Maxim Levitsky <maximlevitsky@gmail.com> http://thread.gmane.org/gmane.comp.video.video4linux/34978/focus=34981 Reviewed-by: Ricardo Cerqueira <v4l@cerqueira.org> Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>
Diffstat (limited to 'drivers/media/video/videobuf-dma-sg.c')
-rw-r--r--drivers/media/video/videobuf-dma-sg.c32
1 files changed, 27 insertions, 5 deletions
diff --git a/drivers/media/video/videobuf-dma-sg.c b/drivers/media/video/videobuf-dma-sg.c
index 0939ede831ab..05dd38343fa3 100644
--- a/drivers/media/video/videobuf-dma-sg.c
+++ b/drivers/media/video/videobuf-dma-sg.c
@@ -134,8 +134,8 @@ void videobuf_dma_init(struct videobuf_dmabuf *dma)
dma->magic = MAGIC_DMABUF;
}
-int videobuf_dma_init_user(struct videobuf_dmabuf *dma, int direction,
- unsigned long data, unsigned long size)
+static int videobuf_dma_init_user_locked(struct videobuf_dmabuf *dma,
+ int direction, unsigned long data, unsigned long size)
{
unsigned long first,last;
int err, rw = 0;
@@ -160,12 +160,12 @@ int videobuf_dma_init_user(struct videobuf_dmabuf *dma, int direction,
dma->varea = (void *) data;
- down_read(&current->mm->mmap_sem);
+
err = get_user_pages(current,current->mm,
data & PAGE_MASK, dma->nr_pages,
rw == READ, 1, /* force */
dma->pages, NULL);
- up_read(&current->mm->mmap_sem);
+
if (err != dma->nr_pages) {
dma->nr_pages = (err >= 0) ? err : 0;
dprintk(1,"get_user_pages: err=%d [%d]\n",err,dma->nr_pages);
@@ -174,6 +174,17 @@ int videobuf_dma_init_user(struct videobuf_dmabuf *dma, int direction,
return 0;
}
+int videobuf_dma_init_user(struct videobuf_dmabuf *dma, int direction,
+ unsigned long data, unsigned long size)
+{
+ int ret;
+ down_read(&current->mm->mmap_sem);
+ ret = videobuf_dma_init_user_locked(dma, direction, data, size);
+ up_read(&current->mm->mmap_sem);
+
+ return ret;
+}
+
int videobuf_dma_init_kernel(struct videobuf_dmabuf *dma, int direction,
int nr_pages)
{
@@ -469,13 +480,24 @@ static int __videobuf_iolock (struct videobuf_queue* q,
pages );
if (0 != err)
return err;
- } else {
+ } else if (vb->memory == V4L2_MEMORY_USERPTR) {
/* dma directly to userspace */
err = videobuf_dma_init_user( &mem->dma,
PCI_DMA_FROMDEVICE,
vb->baddr,vb->bsize );
if (0 != err)
return err;
+ } else {
+ /* NOTE: HACK: videobuf_iolock on V4L2_MEMORY_MMAP
+ buffers can only be called from videobuf_qbuf
+ we take current->mm->mmap_sem there, to prevent
+ locking inversion, so don't take it here */
+
+ err = videobuf_dma_init_user_locked(&mem->dma,
+ PCI_DMA_FROMDEVICE,
+ vb->baddr, vb->bsize);
+ if (0 != err)
+ return err;
}
break;
case V4L2_MEMORY_OVERLAY: