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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>
This commit is contained in:
Maxim Levitsky 2007-09-27 20:34:09 -03:00 committed by Mauro Carvalho Chehab
parent 851c0c96b2
commit 9900132f34
2 changed files with 34 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
drivers/media/video/videobuf-core.c
View File

@ -349,6 +349,9 @@ int videobuf_qbuf(struct videobuf_queue *q,
MAGIC_CHECK(q->int_ops->magic,MAGIC_QTYPE_OPS);
if (b->memory == V4L2_MEMORY_MMAP)
down_read(&current->mm->mmap_sem);
mutex_lock(&q->lock);
retval = -EBUSY;
if (q->reading) {
@ -434,6 +437,10 @@ int videobuf_qbuf(struct videobuf_queue *q,
done:
mutex_unlock(&q->lock);
if (b->memory == V4L2_MEMORY_MMAP)
up_read(&current->mm->mmap_sem);
return retval;
}

32
drivers/media/video/videobuf-dma-sg.c
View File

@ -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: