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charset="us-ascii" Content-ID: <6635582B67FD7443A8D341E41B3F7D55@namprd15.prod.outlook.com> MIME-Version: 1.0 X-OriginatorOrg: fb.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: SA1PR15MB5109.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 3785dc6a-d8f9-41c6-5bc5-08da69d601ed X-MS-Exchange-CrossTenant-originalarrivaltime: 19 Jul 2022 22:28:30.2284 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: MsGGXG90lwGA5BDdq44uhT4lHmZpA4DIARIIOt/Ev42uvK5Fb3vvCfFprRG0L9gXRVcWWJaoAyRR6Ezpz0v7YA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: MWHPR15MB1549 X-Proofpoint-ORIG-GUID: ZgVQf-gbvpAO586glCl6aEkY3v3X90Iy X-Proofpoint-GUID: ZgVQf-gbvpAO586glCl6aEkY3v3X90Iy X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.883,Hydra:6.0.517,FMLib:17.11.122.1 definitions=2022-07-19_08,2022-07-19_01,2022-06-22_01 Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org > On Jul 19, 2022, at 11:32 AM, Steven Rostedt wrote: > > On Mon, 18 Jul 2022 16:59:51 +0000 > Song Liu wrote: > >>>> vim +/direct_mutex_locked +8197 kernel/trace/ftrace.c >>>> >>>> 8182 >>>> 8183 /** >>>> 8184 * register_ftrace_function - register a function for profiling >>>> 8185 * @ops: ops structure that holds the function for profiling. >>>> 8186 * >>>> 8187 * Register a function to be called by all functions in the >>>> 8188 * kernel. >>>> 8189 * >>>> 8190 * Note: @ops->func and all the functions it calls must be labeled >>>> 8191 * with "notrace", otherwise it will go into a >>>> 8192 * recursive loop. >>>> 8193 */ >>>> 8194 int register_ftrace_function(struct ftrace_ops *ops) >>>> 8195 __releases(&direct_mutex) >>>> 8196 { >>>>> 8197 bool direct_mutex_locked = false; >>>> 8198 int ret; >>>> 8199 >>>> 8200 ftrace_ops_init(ops); >>>> 8201 >>>> 8202 ret = prepare_direct_functions_for_ipmodify(ops); >>>> 8203 if (ret < 0) >>>> 8204 return ret; >>>> 8205 else if (ret == 1) >>>> 8206 direct_mutex_locked = true; >>> >>> Honestly, this is another horrible trick. Would it be possible to >>> call prepare_direct_functions_for_ipmodify() with direct_mutex >>> already taken? > > Agreed. I'm not sure why I didn't notice this in the other versions. > Probably was looking too much at the other logic. :-/ > >>> >>> I mean something like: >>> >>> mutex_lock(&direct_mutex); >>> >>> ret = prepare_direct_functions_for_ipmodify(ops); >>> if (ret) >>> goto out: >>> >>> mutex_lock(&ftrace_lock); >>> ret = ftrace_startup(ops, 0); >>> mutex_unlock(&ftrace_lock); >>> >>> out: >>> mutex_unlock(&direct_mutex); >>> return ret; >> >> Yeah, we can actually do something like this. We can also move the >> ops->flags & FTRACE_OPS_FL_IPMODIFY check to >> register_ftrace_function(), so we only lock direct_mutex when when >> it is necessary. > > No need. Just take the direct_mutex, and perhaps add a: > > lockdep_assert_held(&direct_mutex); > > in the prepare_direct_functions_for_ipmodify(). > > This is far from a fast path to do any tricks in trying to optimize it. Got it. I will fix these and send v5. Thanks, Song