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authorHans Verkuil <hverkuil@xs4all.nl>2014-01-03 08:10:49 -0300
committerMauro Carvalho Chehab <m.chehab@samsung.com>2014-02-04 06:29:46 -0200
commitcca36e2eecec2b8fc869a50ffd3bd0adeed92b8b (patch)
tree88a5b83d47de51a8af1877241dbc753a5ad665ea /drivers/media/v4l2-core/videobuf-dma-contig.c
parent50c88544d225baadd6de1c4365d4ed16cc942a37 (diff)
[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 <hans.verkuil@cisco.com> Cc: <stable@vger.kernel.org> # for v3.11 and up Cc: Al Viro <viro@ZenIV.linux.org.uk> Reported-by: Pete Eberlein <pete@sensoray.com> Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
Diffstat (limited to 'drivers/media/v4l2-core/videobuf-dma-contig.c')
-rw-r--r--drivers/media/v4l2-core/videobuf-dma-contig.c12
1 files changed, 5 insertions, 7 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 = {