From: Peter Zijlstra <peterz@infradead.org> To: rjw@rjwysocki.net, oleg@redhat.com, mingo@kernel.org, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, mgorman@suse.de, Will Deacon <will@kernel.org> Cc: linux-kernel@vger.kernel.org, peterz@infradead.org, tj@kernel.org, linux-pm@vger.kernel.org Subject: [PATCH v3 5/6] sched,ptrace: Avoid relying on __TASK_TRACED | __TASK_STOPPED Date: Sat, 09 Oct 2021 12:07:59 +0200 [thread overview] Message-ID: <20211009101445.090696671@infradead.org> (raw) In-Reply-To: <20211009100754.690769957@infradead.org> Make ->ptrace/->jobctl the canonical state, this allows us to play games with __state (such as freezing). The wait_task_inactive() usage will be fixed up later, once we have additional TASK_state. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- include/linux/sched.h | 27 ++++++++++++++++++++++----- kernel/ptrace.c | 16 +++++++++------- 2 files changed, 31 insertions(+), 12 deletions(-) --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -118,11 +118,9 @@ struct task_group; #define task_is_running(task) (READ_ONCE((task)->__state) == TASK_RUNNING) -#define task_is_traced(task) ((READ_ONCE(task->__state) & __TASK_TRACED) != 0) - -#define task_is_stopped(task) ((READ_ONCE(task->__state) & __TASK_STOPPED) != 0) - -#define task_is_stopped_or_traced(task) ((READ_ONCE(task->__state) & (__TASK_STOPPED | __TASK_TRACED)) != 0) +#define task_is_traced(task) ((task)->ptrace & PT_STOPPED) +#define task_is_stopped(task) ((task)->jobctl & JOBCTL_STOP_PENDING) +#define task_is_stopped_or_traced(task) (task_is_stopped(task) || task_is_traced(task)) /* * Special states are those that do not use the normal wait-loop pattern. See @@ -228,6 +226,25 @@ struct task_group; } while (0) /* + * task_cond_set_special_state() is a cmpxchg like operation on task->state. + * + * This operation isn't safe in general and should only be used to transform + * one (special) blocked state into another, such as: + * TASK_STOPPED <-> TASK_FROZEN. + */ +#define task_cond_set_special_state(task, cond_state) \ + ({ \ + struct task_struct *__p = (task); \ + unsigned long __flags; /* may shadow */ \ + unsigned int __state; \ + raw_spin_lock_irqsave(&__p->pi_lock, __flags); \ + if ((__state = (cond_state))) \ + WRITE_ONCE(__p->__state, __state); \ + raw_spin_unlock_irqrestore(&__p->pi_lock, __flags); \ + !!__state; \ + }) + +/* * PREEMPT_RT specific variants for "sleeping" spin/rwlocks * * RT's spin/rwlock substitutions are state preserving. The state of the --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -207,7 +207,8 @@ static bool ptrace_freeze_traced(struct !__fatal_signal_pending(task)) { task->ptrace &= ~PT_STOPPED_MASK; task->ptrace |= PT_STOPPED; - WRITE_ONCE(task->__state, __TASK_TRACED); + /* *TASK_TRACED -> __TASK_TRACED */ + task_cond_set_special_state(task, !!(task->__state & __TASK_TRACED) * __TASK_TRACED); ret = true; } spin_unlock_irq(&task->sighand->siglock); @@ -217,7 +218,7 @@ static bool ptrace_freeze_traced(struct static void ptrace_unfreeze_traced(struct task_struct *task) { - if (READ_ONCE(task->__state) != __TASK_TRACED) + if (!task_is_traced(task)) return; WARN_ON(!task->ptrace || task->parent != current); @@ -227,13 +228,14 @@ static void ptrace_unfreeze_traced(struc * Recheck state under the lock to close this race. */ spin_lock_irq(&task->sighand->siglock); - if (READ_ONCE(task->__state) == __TASK_TRACED) { + if (task_is_traced(task)) { if (__fatal_signal_pending(task)) { task->ptrace &= ~PT_STOPPED_MASK; wake_up_state(task, __TASK_TRACED); } else { task->ptrace |= PT_STOPPED_MASK; - WRITE_ONCE(task->__state, TASK_TRACED); + /* *TASK_TRACED -> TASK_TRACED */ + task_cond_set_special_state(task, !!(task->__state & __TASK_TRACED) * TASK_TRACED); } } spin_unlock_irq(&task->sighand->siglock); @@ -269,7 +271,7 @@ static int ptrace_check_attach(struct ta */ read_lock(&tasklist_lock); if (child->ptrace && child->parent == current) { - WARN_ON(READ_ONCE(child->__state) == __TASK_TRACED); +// WARN_ON(READ_ONCE(child->__state) == __TASK_TRACED); /* * child->sighand can't be NULL, release_task() * does ptrace_unlink() before __exit_signal(). @@ -280,13 +282,13 @@ static int ptrace_check_attach(struct ta read_unlock(&tasklist_lock); if (!ret && !ignore_state) { - if (!wait_task_inactive(child, __TASK_TRACED)) { + if (!wait_task_inactive(child, __TASK_TRACED)) { // XXX mooo!!! /* * This can only happen if may_ptrace_stop() fails and * ptrace_stop() changes ->state back to TASK_RUNNING, * so we should not worry about leaking __TASK_TRACED. */ - WARN_ON(READ_ONCE(child->__state) == __TASK_TRACED); +// WARN_ON(READ_ONCE(child->__state) == __TASK_TRACED); ret = -ESRCH; } }
next prev parent reply other threads:[~2021-10-09 10:20 UTC|newest] Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-10-09 10:07 [PATCH v3 0/6] Freezer rewrite Peter Zijlstra 2021-10-09 10:07 ` [PATCH v3 1/6] freezer: Have {,un}lock_system_sleep() save/restore flags Peter Zijlstra 2021-10-14 8:58 ` Will Deacon 2021-10-09 10:07 ` [PATCH v3 2/6] freezer,umh: Clean up freezer/initrd interaction Peter Zijlstra 2021-10-14 9:13 ` Will Deacon 2021-10-09 10:07 ` [PATCH v3 3/6] ptrace: Order and comment PT_flags Peter Zijlstra 2021-10-14 9:31 ` Will Deacon 2021-10-14 14:27 ` Peter Zijlstra 2021-10-09 10:07 ` [PATCH v3 4/6] ptrace: Track __TASK_TRACED state in p->ptrace Peter Zijlstra 2021-10-09 10:07 ` Peter Zijlstra [this message] 2021-10-09 10:08 ` [PATCH v3 6/6] freezer,sched: Rewrite core freezer logic Peter Zijlstra 2021-10-18 13:36 ` Peter Zijlstra
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