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Biederman" Cc: Linus Torvalds , linux@leemhuis.info, nicolas.dichtel@6wind.com, axboe@kernel.dk, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, mst@redhat.com, sgarzare@redhat.com, jasowang@redhat.com, stefanha@redhat.com, brauner@kernel.org References: <20230523121506.GA6562@redhat.com> <87bkib6nxr.fsf@email.froward.int.ebiederm.org> <20230524141022.GA19091@redhat.com> <87ttw1zt4i.fsf@email.froward.int.ebiederm.org> <20230525115512.GA9229@redhat.com> <87y1lcxwcj.fsf@email.froward.int.ebiederm.org> <87cz2mrtnk.fsf@email.froward.int.ebiederm.org> <87mt1pmezu.fsf@email.froward.int.ebiederm.org> <20230529111859.GA15193@redhat.com> Content-Language: en-US From: michael.christie@oracle.com In-Reply-To: <20230529111859.GA15193@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: CH2PR07CA0036.namprd07.prod.outlook.com (2603:10b6:610:20::49) To CY8PR10MB7243.namprd10.prod.outlook.com (2603:10b6:930:7c::10) 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0NMNqWAq3CnQ+3ZX8+BuomgD82bWJycd9aeUcMjokNJBrw431kKj33oNQln29YoZIora6zoiirPgBXMS6+njiMrGu6386HiNY7Ua3MRxP8g= X-MS-Exchange-Transport-CrossTenantHeadersStamped: CO1PR10MB4769 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.254,Aquarius:18.0.957,Hydra:6.0.573,FMLib:17.11.176.26 definitions=2023-05-29_10,2023-05-29_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 mlxlogscore=999 adultscore=0 malwarescore=0 bulkscore=0 suspectscore=0 mlxscore=0 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2304280000 definitions=main-2305290135 X-Proofpoint-ORIG-GUID: xEkKuhDx3HvoKjRwJmnQFGIIZXIXmfzO X-Proofpoint-GUID: xEkKuhDx3HvoKjRwJmnQFGIIZXIXmfzO Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/29/23 6:19 AM, Oleg Nesterov wrote: > On 05/27, Eric W. Biederman wrote: >> >> Looking forward I don't see not asking the worker threads to stop >> for the coredump right now causing any problems in the future. >> So I think we can use this to resolve the coredump issue I spotted. > > But we have almost the same problem with exec. > > Execing thread will wait for vhost_worker() while vhost_worker will wait for > .release -> vhost_task_stop(). For this type of case, what is the goal or correct behavior in the end? When get_signal returns true we can code things like you mention below and clean up the task_struct. However, we now have a non-functioning vhost device open and just sitting around taking up memory and it can't do any IO. For this type of case, do we expect just not to crash/hang, or was this new exec'd thread suppose to be able to use the vhost device? I would normally say it probably wants to use the vhost device still. However, I don't think this comes up so just not hanging might be ok. Before 6.4-rc1, we ignored signals so it would have worked if we are concerned about a possible regression if this was a common thing. > > And even O_CLOEXEC won't help, do_close_on_exec() is called after de_thread(). > > Or suppose that vhost_worker's sub-thread forks a child with CLONE_FILES... You mean the vhost_task's task/thread doing a function that does a copy_process right? That type of thing is not needed. I can add a check in vhost_task_create for this so new code doesn't try to do it. I don't think it will come up that some code vhost is using will call kernel_thread/copy_process directly since those calls are so rare and the functions are not exported to modules. > > If we want CLONE_THREAD, I think vhost_worker() should exit after get_signal() > returns SIGKILL. Perhaps it should "disable" vhost_work_queue() somehow and > flush the pending works on ->work_list before exit, I dunno. But imo it should > not wait for the final fput(). > > Oleg. >