From cca36e2eecec2b8fc869a50ffd3bd0adeed92b8b Mon Sep 17 00:00:00 2001 From: Hans Verkuil Date: Fri, 3 Jan 2014 08:10:49 -0300 Subject: [media] Revert "[media] videobuf_vm_{open,close} race fixes" This reverts commit a242f426108c284049a69710f871cc9f11b13e61. That commit actually caused deadlocks, rather then fixing them. If ext_lock is set to NULL (otherwise videobuf_queue_lock doesn't do anything), then you get this deadlock: The driver's mmap function calls videobuf_mmap_mapper which calls videobuf_queue_lock on q. videobuf_mmap_mapper calls __videobuf_mmap_mapper, __videobuf_mmap_mapper calls videobuf_vm_open and videobuf_vm_open calls videobuf_queue_lock on q (introduced by above patch): deadlocked. This affects drivers using dma-contig and dma-vmalloc. Only dma-sg is not affected since it doesn't call videobuf_vm_open from __videobuf_mmap_mapper. Most drivers these days have a non-NULL ext_lock. Those that still use NULL there are all fairly obscure drivers, which is why this hasn't been seen earlier. Since everything worked perfectly fine for many years I prefer to just revert this patch rather than trying to fix it. videobuf is quite fragile and I rather not touch it too much. Work is (slowly) progressing to move everything over to vb2 or at the very least use non-NULL ext_lock in videobuf. Signed-off-by: Hans Verkuil Cc: # for v3.11 and up Cc: Al Viro Reported-by: Pete Eberlein Signed-off-by: Mauro Carvalho Chehab --- drivers/media/v4l2-core/videobuf-vmalloc.c | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) (limited to 'drivers/media/v4l2-core/videobuf-vmalloc.c') diff --git a/drivers/media/v4l2-core/videobuf-vmalloc.c b/drivers/media/v4l2-core/videobuf-vmalloc.c index 1365c651c177..2ff7fcc77b11 100644 --- a/drivers/media/v4l2-core/videobuf-vmalloc.c +++ b/drivers/media/v4l2-core/videobuf-vmalloc.c @@ -54,14 +54,11 @@ MODULE_LICENSE("GPL"); static void videobuf_vm_open(struct vm_area_struct *vma) { struct videobuf_mapping *map = vma->vm_private_data; - struct videobuf_queue *q = map->q; dprintk(2, "vm_open %p [count=%u,vma=%08lx-%08lx]\n", map, map->count, vma->vm_start, vma->vm_end); - videobuf_queue_lock(q); map->count++; - videobuf_queue_unlock(q); } static void videobuf_vm_close(struct vm_area_struct *vma) @@ -73,11 +70,12 @@ static void videobuf_vm_close(struct vm_area_struct *vma) dprintk(2, "vm_close %p [count=%u,vma=%08lx-%08lx]\n", map, map->count, vma->vm_start, vma->vm_end); - videobuf_queue_lock(q); - if (!--map->count) { + map->count--; + if (0 == map->count) { struct videobuf_vmalloc_memory *mem; dprintk(1, "munmap %p q=%p\n", map, q); + videobuf_queue_lock(q); /* We need first to cancel streams, before unmapping */ if (q->streaming) @@ -116,8 +114,8 @@ static void videobuf_vm_close(struct vm_area_struct *vma) kfree(map); + videobuf_queue_unlock(q); } - videobuf_queue_unlock(q); return; } -- cgit