path: root/drivers/media/v4l2-core/videobuf2-vmalloc.c
diff options
authorJan Kara <jack@suse.cz>2015-07-13 11:55:43 -0300
committerMauro Carvalho Chehab <mchehab@osg.samsung.com>2015-08-16 13:01:10 -0300
commit0f6e2825ce916eed882996bb6e9148c13ecebefd (patch)
treea08735e1623e370f32f255a27994cdb6e62c2284 /drivers/media/v4l2-core/videobuf2-vmalloc.c
parent27c039750c8ff1297632e424a4674732cc4c3c70 (diff)
[media] vb2: Push mmap_sem down to memops
Currently vb2 core acquires mmap_sem just around call to __qbuf_userptr(). However since commit f035eb4e976ef5 (videobuf2: fix lockdep warning) it isn't necessary to acquire it so early as we no longer have to drop queue mutex before acquiring mmap_sem. So push acquisition of mmap_sem down into .get_userptr memop so that the semaphore is acquired for a shorter time and it is clearer what it is needed for. Note that we also need mmap_sem in .put_userptr memop since that ends up calling vb2_put_vma() which calls vma->vm_ops->close() which should be called with mmap_sem held. However we didn't hold mmap_sem in some code paths anyway (e.g. when called via vb2_ioctl_reqbufs() -> __vb2_queue_free() -> vb2_dma_sg_put_userptr()) and getting mmap_sem in put_userptr() introduces a lock inversion with queue->mmap_lock in the above mentioned call path. Luckily this whole locking mess will get resolved once we convert videobuf2 core to the new mm helper which avoids the need for mmap_sem in .put_userptr memop altogether. Signed-off-by: Jan Kara <jack@suse.cz> Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Diffstat (limited to 'drivers/media/v4l2-core/videobuf2-vmalloc.c')
1 files changed, 3 insertions, 1 deletions
diff --git a/drivers/media/v4l2-core/videobuf2-vmalloc.c b/drivers/media/v4l2-core/videobuf2-vmalloc.c
index 2fe4c27f524a..63bef959623e 100644
--- a/drivers/media/v4l2-core/videobuf2-vmalloc.c
+++ b/drivers/media/v4l2-core/videobuf2-vmalloc.c
@@ -89,7 +89,7 @@ static void *vb2_vmalloc_get_userptr(void *alloc_ctx, unsigned long vaddr,
offset = vaddr & ~PAGE_MASK;
buf->size = size;
+ down_read(&current->mm->mmap_sem);
vma = find_vma(current->mm, vaddr);
if (vma && (vma->vm_flags & VM_PFNMAP) && (vma->vm_pgoff)) {
if (vb2_get_contig_userptr(vaddr, size, &vma, &physp))
@@ -121,6 +121,7 @@ static void *vb2_vmalloc_get_userptr(void *alloc_ctx, unsigned long vaddr,
if (!buf->vaddr)
goto fail_get_user_pages;
+ up_read(&current->mm->mmap_sem);
buf->vaddr += offset;
return buf;
@@ -133,6 +134,7 @@ fail_get_user_pages:
+ up_read(&current->mm->mmap_sem);
return NULL;

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