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Fri, 23 Jul 2021 12:34:18 +0000 Subject: Re: [PATCH] dma-buf: WARN on dmabuf release with pending attachments To: Charan Teja Reddy , sumit.semwal@linaro.org Cc: linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org, vinmenon@codeaurora.org References: <1627043468-16381-1-git-send-email-charante@codeaurora.org> From: =?UTF-8?Q?Christian_K=c3=b6nig?= Message-ID: Date: Fri, 23 Jul 2021 14:34:13 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 In-Reply-To: <1627043468-16381-1-git-send-email-charante@codeaurora.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-ClientProxiedBy: PR0P264CA0085.FRAP264.PROD.OUTLOOK.COM (2603:10a6:100:18::25) To MN2PR12MB3775.namprd12.prod.outlook.com (2603:10b6:208:159::19) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [IPv6:2a02:908:1252:fb60:4ae7:63c0:5e49:6388] (2a02:908:1252:fb60:4ae7:63c0:5e49:6388) by PR0P264CA0085.FRAP264.PROD.OUTLOOK.COM (2603:10a6:100:18::25) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4352.25 via Frontend Transport; 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// Clients attach to the dmabuf > o Here the kernel does some slab allocations, say for > dma_buf_attachment and may be some other slab allocation in the > dmabuf->ops->attach(). > c) Client may need to do dma_buf_map_attachment(). > d) Accordingly dma_buf_unmap_attachment() should be called. > e) dma_buf_detach () // Clients detach to the dmabuf. > o Here the slab allocations made in b) are freed. > f) dma_buf_put(dmabuf) // Can free the dmabuf if it is the last > reference. > > Now say an erroneous client failed at step c) above thus it directly > called dma_buf_put(), step f) above. Considering that it may be the last > reference to the dmabuf, buffer will be freed with pending attachments > left to the dmabuf which can show up as the 'memory leak'. This should > at least be reported as the WARN(). > > Signed-off-by: Charan Teja Reddy Good idea. I would expect a crash immediately, but from such a backtrace it is quite hard to tell what the problem is. Patch is Reviewed-by: Christian König and I'm going to push this to drm-misc-next on Monday if nobody objects. Thanks, Christian. > --- > drivers/dma-buf/dma-buf.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c > index 511fe0d..733c8b1 100644 > --- a/drivers/dma-buf/dma-buf.c > +++ b/drivers/dma-buf/dma-buf.c > @@ -79,6 +79,7 @@ static void dma_buf_release(struct dentry *dentry) > if (dmabuf->resv == (struct dma_resv *)&dmabuf[1]) > dma_resv_fini(dmabuf->resv); > > + WARN_ON(!list_empty(&dmabuf->attachments)); > module_put(dmabuf->owner); > kfree(dmabuf->name); > kfree(dmabuf);