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[34.197.84.77]) by smtp.gmail.com with ESMTPSA id o25sm346909qkm.42.2020.08.31.22.42.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 31 Aug 2020 22:42:29 -0700 (PDT) Date: Tue, 1 Sep 2020 05:42:27 +0000 From: Bjorn Andersson To: Rob Clark Cc: dri-devel , "list@263.net:IOMMU DRIVERS , Joerg Roedel ," , linux-arm-msm , Sai Prakash Ranjan , Will Deacon , freedreno , Sibi Sankar , Vivek Gautam , Stephen Boyd , Robin Murphy , Joerg Roedel , "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" , Rob Clark , Sean Paul , David Airlie , Daniel Vetter , open list Subject: Re: [PATCH 01/19] drm/msm: remove dangling submitqueue references Message-ID: <20200901054227.GB54956@uller> References: <20200810222657.1841322-1-jcrouse@codeaurora.org> <20200814024114.1177553-2-robdclark@gmail.com> <20200901023517.GA54956@uller> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 01 Sep 03:42 UTC 2020, Rob Clark wrote: > On Mon, Aug 31, 2020 at 7:35 PM Bjorn Andersson > wrote: > > > > On Fri 14 Aug 02:40 UTC 2020, Rob Clark wrote: > > > > > From: Rob Clark > > > > > > Currently it doesn't matter, since we free the ctx immediately. But > > > when we start refcnt'ing the ctx, we don't want old dangling list > > > entries to hang around. > > > > > > Signed-off-by: Rob Clark > > > --- > > > drivers/gpu/drm/msm/msm_submitqueue.c | 4 +++- > > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > > > diff --git a/drivers/gpu/drm/msm/msm_submitqueue.c b/drivers/gpu/drm/msm/msm_submitqueue.c > > > index a1d94be7883a..90c9d84e6155 100644 > > > --- a/drivers/gpu/drm/msm/msm_submitqueue.c > > > +++ b/drivers/gpu/drm/msm/msm_submitqueue.c > > > @@ -49,8 +49,10 @@ void msm_submitqueue_close(struct msm_file_private *ctx) > > > * No lock needed in close and there won't > > > * be any more user ioctls coming our way > > > */ > > > - list_for_each_entry_safe(entry, tmp, &ctx->submitqueues, node) > > > + list_for_each_entry_safe(entry, tmp, &ctx->submitqueues, node) { > > > + list_del(&entry->node); > > > > If you refcount ctx, what does that do for the entries in the submit > > queue? > > > > "entry" here is kref'ed, but you're popping it off the list regardless > > of the put ends up freeing the object or not - which afaict would mean > > leaking the object. > > > > What ends up happening is the submit has reference to submit-queue, > which has reference to the ctx.. the submitqueue could be alive still > pending in-flight submits (in a later patch), but dead from the PoV of > userspace interface. > > We aren't relying (or at least aren't in the end, and I *think* I > didn't miss anything in the middle) relying on ctx->submitqueues list > to clean anything up in the end, just track what is still a valid > submitqueue from userspace PoV > Looks reasonable, thanks for the explanation. > BR, > -R > > > > > On the other hand, with the current implementation an object with higher > > refcount with adjacent objects of single refcount would end up with > > dangling pointers after the put. So in itself this change seems like a > > net gain, but I'm wondering about the plan described in the commit > > message. > > > > Regards, > > Bjorn > > > > > msm_submitqueue_put(entry); > > > + } > > > } > > > > > > int msm_submitqueue_create(struct drm_device *drm, struct msm_file_private *ctx, > > > -- > > > 2.26.2 > > >