lkml.org 
[lkml]   [2021]   [Oct]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [Linaro-mm-sig] [PATCH] dma-buf: add attachments empty check for dma_buf_release
From
Date


Am 19.10.21 um 14:41 schrieb Daniel Vetter:
> On Tue, Oct 19, 2021 at 08:23:45PM +0800, guangming.cao@mediatek.com wrote:
>> From: Guangming Cao <Guangming.Cao@mediatek.com>
>>
>> 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@mediatek.com>
> 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.

>
> 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));".

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
>>

\
 
 \ /
  Last update: 2021-10-19 17:38    [W:2.586 / U:0.032 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site