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Sat, 26 Jul 2025 14:50:10 -0700 (PDT) Date: Sat, 26 Jul 2025 14:50:07 -0700 From: Sultan Alsawaf To: "Du, Bin" Cc: mchehab@kernel.org, hverkuil@xs4all.nl, laurent.pinchart+renesas@ideasonboard.com, bryan.odonoghue@linaro.org, sakari.ailus@linux.intel.com, prabhakar.mahadev-lad.rj@bp.renesas.com, linux-media@vger.kernel.org, linux-kernel@vger.kernel.org, pratap.nirujogi@amd.com, benjamin.chan@amd.com, king.li@amd.com, gjorgji.rosikopulos@amd.com, Phil.Jawich@amd.com, Dominic.Antony@amd.com Subject: Re: [PATCH v2 6/8] media: platform: amd: isp4 video node and buffers handling added Message-ID: References: <20250618091959.68293-1-Bin.Du@amd.com> <20250618091959.68293-7-Bin.Du@amd.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Sat, Jul 26, 2025 at 02:41:41PM -0700, Sultan Alsawaf wrote: > On Fri, Jul 25, 2025 at 05:22:41PM +0800, Du, Bin wrote: > > > > + dev_warn(buf->dev, "ignore buffer free, refcount %u > 0", > > > > + refcount_read(&buf->refcount)); > > > > > > This refcount_read() is a possible use-after-free because `buf` is accessed > > > after isp4vid_vb2_put() puts its reference to `buf`. So something else could put > > > the last reference to `buf` and free it after this refcount dec but before the > > > refcount_read(). Maybe just remove this dev_warn() entirely? > > > > > The warning is important to debug mem related issue, plan to keep it but > > without accessing buf or buf->refcount here. Do you think it acceptible? > > Yes, that sounds good. So something like this: > `dev_warn(buf->dev, "ignore buffer free, refcount > 0");` Sorry, to fix the dev_warn() we need to make a copy of buf->dev first: --- a/drivers/media/platform/amd/isp4/isp4_video.c +++ b/drivers/media/platform/amd/isp4/isp4_video.c @@ -584,8 +584,9 @@ static void isp4vid_vb2_put(void *buf_priv) { struct isp4vid_vb2_buf *buf = (struct isp4vid_vb2_buf *)buf_priv; struct amdgpu_bo *bo = (struct amdgpu_bo *)buf->bo; + struct device *dev = buf->dev; - dev_dbg(buf->dev, + dev_dbg(dev, "release isp user bo 0x%llx size %ld refcount %d is_expbuf %d", buf->gpu_addr, buf->size, buf->refcount.refs.counter, buf->is_expbuf); @@ -601,8 +602,7 @@ static void isp4vid_vb2_put(void *buf_priv) kfree(buf); buf = NULL; } else { - dev_warn(buf->dev, "ignore buffer free, refcount %u > 0", - refcount_read(&buf->refcount)); + dev_warn(dev, "ignore buffer free, refcount > 0\n"); } } -- Sultan