From cca36e2eecec2b8fc869a50ffd3bd0adeed92b8b Mon Sep 17 00:00:00 2001 From: Hans Verkuil Date: Fri, 3 Jan 2014 08:10:49 -0300 Subject: [PATCH] [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-dma-contig.c | 12 +++++------- drivers/media/v4l2-core/videobuf-dma-sg.c | 10 ++++------ drivers/media/v4l2-core/videobuf-vmalloc.c | 10 ++++------ 3 files changed, 13 insertions(+), 19 deletions(-) diff --git a/drivers/media/v4l2-core/videobuf-dma-contig.c b/drivers/media/v4l2-core/videobuf-dma-contig.c index 65411adcd0ea..7e6b209b7002 100644 --- a/drivers/media/v4l2-core/videobuf-dma-contig.c +++ b/drivers/media/v4l2-core/videobuf-dma-contig.c @@ -66,14 +66,11 @@ static void __videobuf_dc_free(struct device *dev, static void videobuf_vm_open(struct vm_area_struct *vma) { struct videobuf_mapping *map = vma->vm_private_data; - struct videobuf_queue *q = map->q; - dev_dbg(q->dev, "vm_open %p [count=%u,vma=%08lx-%08lx]\n", + dev_dbg(map->q->dev, "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) @@ -85,11 +82,12 @@ static void videobuf_vm_close(struct vm_area_struct *vma) dev_dbg(q->dev, "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_dma_contig_memory *mem; dev_dbg(q->dev, "munmap %p q=%p\n", map, q); + videobuf_queue_lock(q); /* We need first to cancel streams, before unmapping */ if (q->streaming) @@ -128,8 +126,8 @@ static void videobuf_vm_close(struct vm_area_struct *vma) kfree(map); + videobuf_queue_unlock(q); } - videobuf_queue_unlock(q); } static const struct vm_operations_struct videobuf_vm_ops = { diff --git a/drivers/media/v4l2-core/videobuf-dma-sg.c b/drivers/media/v4l2-core/videobuf-dma-sg.c index 9db674ccdc68..828e7c10bd70 100644 --- a/drivers/media/v4l2-core/videobuf-dma-sg.c +++ b/drivers/media/v4l2-core/videobuf-dma-sg.c @@ -338,14 +338,11 @@ EXPORT_SYMBOL_GPL(videobuf_dma_free); 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=%d,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) @@ -358,9 +355,10 @@ static void videobuf_vm_close(struct vm_area_struct *vma) dprintk(2, "vm_close %p [count=%d,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) { dprintk(1, "munmap %p q=%p\n", map, q); + videobuf_queue_lock(q); for (i = 0; i < VIDEO_MAX_FRAME; i++) { if (NULL == q->bufs[i]) continue; @@ -376,9 +374,9 @@ static void videobuf_vm_close(struct vm_area_struct *vma) q->bufs[i]->baddr = 0; q->ops->buf_release(q, q->bufs[i]); } + videobuf_queue_unlock(q); kfree(map); } - videobuf_queue_unlock(q); return; } 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; } -- 2.20.1