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Tsirkin" , Mike Christie , Peter Zijlstra , Wander Lairson Costa , Kefeng Wang , Oleg Nesterov , Andrew Morton , "Liam R. Howlett" , Suren Baghdasaryan , Mathieu Desnoyers , Andrei Vagin , Nicholas Piggin , linux-kernel@vger.kernel.org (open list) Cc: Hu Chunyu , Valentin Schneider , Sebastian Andrzej Siewior , Paul McKenney , Steven Rostedt , Luis Goncalves Subject: [PATCH v10 0/2] kernel/fork: beware of __put_task_struct calling context Date: Wed, 14 Jun 2023 09:23:20 -0300 Message-Id: <20230614122323.37957-1-wander@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.1 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H5,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_NONE, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1768681395122027382?= X-GMAIL-MSGID: =?utf-8?q?1768681395122027382?= Under PREEMPT_RT, __put_task_struct() indirectly acquires sleeping locks. Therefore, it can't be called from an non-preemptible context. Instead of calling __put_task_struct() directly, we defer it using call_rcu(). A more natural approach would use a workqueue, but since in PREEMPT_RT, we can't allocate dynamic memory from atomic context, the code would become more complex because we would need to put the work_struct instance in the task_struct and initialize it when we allocate a new task_struct. Changelog ========= v1: * Initial implementation fixing the splat. v2: * Isolate the logic in its own function. * Fix two more cases caught in review. v3: * Change __put_task_struct() to handle the issue internally. v4: * Explain why call_rcu() is safe to call from interrupt context. v5: * Explain why __put_task_struct() doesn't conflict with put_task_sruct_rcu_user. v6: * As per Sebastian's review, revert back the implementation of v2 with a distinct function. * Add a check in put_task_struct() to warning when called from a non-sleepable context. * Address more call sites. v7: * Fix typos. * Add an explanation why the new function doesn't conflict with delayed_free_task(). v8: * Bring back v5. * Fix coding style. v9: * Reorganize to not need ___put_task_struct() by Oleg's suggestion. v10: * Add a patch preventing a splat when compile with CONFIG_PROVE_RAW_LOCK_NESTING. Reported-by: Hu Chunyu Suggested-by: Oleg Nesterov Suggested-by: Valentin Schneider Suggested-by: Peter Zijlstra Cc: Sebastian Andrzej Siewior Cc: Paul McKenney Cc: Steven Rostedt Cc: Luis Goncalves Wander Lairson Costa (2): kernel/fork: beware of __put_task_struct calling context sched: avoid false lockdep splat in put_task_struct() include/linux/sched/task.h | 38 +++++++++++++++++++++++++++++++++++++- kernel/fork.c | 8 ++++++++ 2 files changed, 45 insertions(+), 1 deletion(-)