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Tue, 19 Oct 2021 05:41:17 -0700 (PDT) Received: from phenom.ffwll.local ([2a02:168:57f4:0:efd0:b9e5:5ae6:c2fa]) by smtp.gmail.com with ESMTPSA id p23sm12148807edw.94.2021.10.19.05.41.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 19 Oct 2021 05:41:16 -0700 (PDT) Date: Tue, 19 Oct 2021 14:41:14 +0200 From: Daniel Vetter To: guangming.cao@mediatek.com Cc: Sumit Semwal , Christian =?iso-8859-1?Q?K=F6nig?= , Matthias Brugger , "open list:DMA BUFFER SHARING FRAMEWORK" , "open list:DMA BUFFER SHARING FRAMEWORK" , "moderated list:DMA BUFFER SHARING FRAMEWORK" , open list , "moderated list:ARM/Mediatek SoC support" , "moderated list:ARM/Mediatek SoC support" , wsd_upstream@mediatek.com Subject: Re: [PATCH] dma-buf: add attachments empty check for dma_buf_release Message-ID: Mail-Followup-To: guangming.cao@mediatek.com, Sumit Semwal , Christian =?iso-8859-1?Q?K=F6nig?= , Matthias Brugger , "open list:DMA BUFFER SHARING FRAMEWORK" , "open list:DMA BUFFER SHARING FRAMEWORK" , "moderated list:DMA BUFFER SHARING FRAMEWORK" , open list , "moderated list:ARM/Mediatek SoC support" , "moderated list:ARM/Mediatek SoC support" , wsd_upstream@mediatek.com References: <20211019122345.160555-1-guangming.cao@mediatek.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20211019122345.160555-1-guangming.cao@mediatek.com> X-Operating-System: Linux phenom 5.10.0-8-amd64 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211019_054120_013301_CD97C059 X-CRM114-Status: GOOD ( 29.62 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Oct 19, 2021 at 08:23:45PM +0800, guangming.cao@mediatek.com wrote: > From: Guangming Cao > > 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 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. 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). -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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel