From: Guangming Cao <Guangming.Cao@xxxxxxxxxxxx> On Tue, 2021-10-19 at 23:11 +0200, Daniel Vetter wrote: > On Tue, Oct 19, 2021 at 05:37:27PM +0200, Christian K鰊ig 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. Well, I think it's the finally solution, for current thinking, it maybe bring a high overloading. Just as this revert patch: https://lore.kernel.org/lkml/CA+wgaPMHA+8+LxfGNL+q4=XrdXqfu4TXoWLX7e28z9Z7kPsf-w@xxxxxxxxxxxxxx/ So, we need to find a lightweight way to do this. Guangming > > > > 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). Yes, It's also a error case, I will remove to lock at next version patch. Thanks! Guangming > > > > You also don't need the WARN(!list_empty...) because a few line > > below we > > already have a "WARN_ON(!list_empty(&dmabuf->attachments));". Sorry, could you tell me wich function will check it? I didn't found it so I submit this patch. Guangming > > 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 I also printed dmabuf->exp_name in warn message. The reason adding it here is that some users on ANDROID of dma-buf is not familiar with linux dma-buf or maybe write some problematic code, add this check can find who lost call get_dma_buf or any other api can let let the dma-buf lifecycle is under users' expectation. Add it just like check in dma-fence: https://github.com/torvalds/linux/blob/master/drivers/dma-buf/dma-fence.c#L519 Do you have any suggestion to debug this part? Guangming > 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 > > > > > >
