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Tue, 20 May 2025 07:39:51 +0000 Message-ID: <71accc22-29d1-47ff-909e-e8eb2bdd528a@amd.com> Date: Tue, 20 May 2025 09:39:48 +0200 User-Agent: Mozilla Thunderbird Subject: Re: [RFC 3/3] drm/amdgpu: Add locking to amdgpu_ctx_mgr_entity_fini() To: Tvrtko Ursulin , amd-gfx@lists.freedesktop.org Cc: Alex Deucher References: <20250519163713.11367-1-tvrtko.ursulin@igalia.com> <20250519163713.11367-4-tvrtko.ursulin@igalia.com> Content-Language: en-US From: =?UTF-8?Q?Christian_K=C3=B6nig?= In-Reply-To: <20250519163713.11367-4-tvrtko.ursulin@igalia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ClientProxiedBy: FR4P281CA0306.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:f6::17) To PH7PR12MB5685.namprd12.prod.outlook.com (2603:10b6:510:13c::22) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH7PR12MB5685:EE_|CYYPR12MB9016:EE_ X-MS-Office365-Filtering-Correlation-Id: ad235828-0084-4f0c-98ad-08dd97718176 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|376014|7053199007; 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No, when this function is called when the file descriptor is freed up. So there should never ever be any concurrent user of this. > Problem is I have hit this on a KASAN enabled kernel only _once_ and never > since. In that case it reported amdgpu_ctx_ioctl() had freed the entity > already which would mean the question is could we possibly go through the > mutex_unlock() on one CPU, and another CPU to follow immediately with > file->release (DRM postclose) and see the stale entry. Mhm, it would basically mean that the file descriptor can be closed while some IOCTL on it is still ongoing. I think that this would be extremely ugly and should never ever happen in the first place. Adding the mutex just band aids the issue, but not really fixes it. > Throwing it out there not to forget about it, since I have manage to > lose the KASAN trace already.. If you manage to trigger that again please send it to me ASAP. Thanks, Christian. > > Signed-off-by: Tvrtko Ursulin > Cc: Alex Deucher > Cc: Christian König > --- > drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c > index 85567d0d9545..95b005ed839e 100644 > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c > @@ -927,6 +927,7 @@ static void amdgpu_ctx_mgr_entity_fini(struct amdgpu_ctx_mgr *mgr) > > idp = &mgr->ctx_handles; > > + mutex_lock(&mgr->lock); > idr_for_each_entry(idp, ctx, id) { > if (kref_read(&ctx->refcount) != 1) { > DRM_ERROR("ctx %p is still alive\n", ctx); > @@ -945,6 +946,7 @@ static void amdgpu_ctx_mgr_entity_fini(struct amdgpu_ctx_mgr *mgr) > } > } > } > + mutex_unlock(&mgr->lock); > } > > void amdgpu_ctx_mgr_fini(struct amdgpu_ctx_mgr *mgr)