On Tue, Oct 19, 2021 at 05:37:27PM +0200, Christian König wrote: > > > Am 19.10.21 um 14:41 schrieb Daniel Vetter: > > On Tue, Oct 19, 2021 at 08:23:45PM +0800, guangming.cao@xxxxxxxxxxxx wrote: > > > From: Guangming Cao <Guangming.Cao@xxxxxxxxxxxx> > > > > > > Since there is no mandatory inspection for attachments in dma_buf_release. > > > There will be a case that dma_buf already released but attachment is still > > > in use, which can points to the dmabuf, and it maybe cause > > > some unexpected issues. > > > > > > With IOMMU, when this cases occurs, there will have IOMMU address > > > translation fault(s) followed by this warning, > > > I think it's useful for dma devices to debug issue. > > > > > > Signed-off-by: Guangming Cao <Guangming.Cao@xxxxxxxxxxxx> > > This feels a lot like hand-rolling kobject debugging. If you want to do > > this then I think adding kobject debug support to > > dma_buf/dma_buf_attachment would be better than hand-rolling something > > bespoke here. > > Well I would call that overkill. I think if done right the object debug stuff should be able to give you a backtrace. Which might be useful if you have a dma-buf heaps design where you really have no clue why a buffer was allocated/attached without some hints. > > Also on the patch itself: You don't need the trylock. For correctly > > working code non one else can get at the dma-buf, so no locking needed to > > iterate through the attachment list. For incorrect code the kernel will be > > on fire pretty soon anyway, trying to do locking won't help :-) And > > without the trylock we can catch more bugs (e.g. if you also forgot to > > unlock and not just forgot to detach). > > You also don't need the WARN(!list_empty...) because a few line below we > already have a "WARN_ON(!list_empty(&dmabuf->attachments));". Yeah this patch here alone isn't really that useful I think. Maybe we could add the dmabuf->exp_name or so to that warning, but otherwise the info printed here isn't all that useful for debugging. Grabbing a backtrace of the allocator or attacher otoh should fairly immedialy point at the buggy code. -Daniel > > Christian. > > > -Daniel > > > > > --- > > > drivers/dma-buf/dma-buf.c | 23 +++++++++++++++++++++++ > > > 1 file changed, 23 insertions(+) > > > > > > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c > > > index 511fe0d217a0..672404857d6a 100644 > > > --- a/drivers/dma-buf/dma-buf.c > > > +++ b/drivers/dma-buf/dma-buf.c > > > @@ -74,6 +74,29 @@ static void dma_buf_release(struct dentry *dentry) > > > */ > > > BUG_ON(dmabuf->cb_shared.active || dmabuf->cb_excl.active); > > > + /* attachment check */ > > > + if (dma_resv_trylock(dmabuf->resv) && WARN(!list_empty(&dmabuf->attachments), > > > + "%s err, inode:%08lu size:%08zu name:%s exp_name:%s flags:0x%08x mode:0x%08x, %s\n", > > > + __func__, file_inode(dmabuf->file)->i_ino, dmabuf->size, > > > + dmabuf->name, dmabuf->exp_name, > > > + dmabuf->file->f_flags, dmabuf->file->f_mode, > > > + "Release dmabuf before detach all attachments, dump attach:\n")) { > > > + int attach_cnt = 0; > > > + dma_addr_t dma_addr; > > > + struct dma_buf_attachment *attach_obj; > > > + /* dump all attachment info */ > > > + list_for_each_entry(attach_obj, &dmabuf->attachments, node) { > > > + dma_addr = (dma_addr_t)0; > > > + if (attach_obj->sgt) > > > + dma_addr = sg_dma_address(attach_obj->sgt->sgl); > > > + pr_err("attach[%d]: dev:%s dma_addr:0x%-12lx\n", > > > + attach_cnt, dev_name(attach_obj->dev), dma_addr); > > > + attach_cnt++; > > > + } > > > + pr_err("Total %d devices attached\n\n", attach_cnt); > > > + dma_resv_unlock(dmabuf->resv); > > > + } > > > + > > > dmabuf->ops->release(dmabuf); > > > if (dmabuf->resv == (struct dma_resv *)&dmabuf[1]) > > > -- > > > 2.17.1 > > > > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch