Messages in this thread Patch in this message | | | Date | Tue, 12 Apr 2022 13:44:22 +0200 | From | Peter Zijlstra <> | Subject | [PATCH 1/5] sched,signal,ptrace: Rework TASK_TRACED, TASK_STOPPED state |
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Currently ptrace_stop() / do_signal_stop() rely on the special states TASK_TRACED and TASK_STOPPED resp. to keep unique state. That is, this state exists only in task->__state and nowhere else.
There's two spots of bother with this:
- PREEMPT_RT has task->saved_state which complicates matters, meaning task_is_{traced,stopped}() needs to check an additional variable.
- An alternative freezer implementation that itself relies on a special TASK state would loose TASK_TRACED/TASK_STOPPED and will result in misbehaviour.
As such, add additional state to task->jobctl to track this state outside of task->__state.
NOTE: this doesn't actually fix anything yet, just adds extra state.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- include/linux/sched.h | 8 +++----- include/linux/sched/jobctl.h | 8 ++++++++ include/linux/sched/signal.h | 15 ++++++++++++++- kernel/ptrace.c | 18 ++++++++++++++---- kernel/signal.c | 9 ++++++--- 5 files changed, 45 insertions(+), 13 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) ((READ_ONCE(task->jobctl) & JOBCTL_TRACED) != 0) +#define task_is_stopped(task) ((READ_ONCE(task->jobctl) & JOBCTL_STOPPED) != 0) +#define task_is_stopped_or_traced(task) ((READ_ONCE(task->jobctl) & (JOBCTL_STOPPED | JOBCTL_TRACED)) != 0) /* * Special states are those that do not use the normal wait-loop pattern. See --- a/include/linux/sched/jobctl.h +++ b/include/linux/sched/jobctl.h @@ -20,6 +20,10 @@ struct task_struct; #define JOBCTL_LISTENING_BIT 22 /* ptracer is listening for events */ #define JOBCTL_TRAP_FREEZE_BIT 23 /* trap for cgroup freezer */ +#define JOBCTL_STOPPED_BIT 24 +#define JOBCTL_TRACED_BIT 25 +#define JOBCTL_TRACED_FROZEN_BIT 26 + #define JOBCTL_STOP_DEQUEUED (1UL << JOBCTL_STOP_DEQUEUED_BIT) #define JOBCTL_STOP_PENDING (1UL << JOBCTL_STOP_PENDING_BIT) #define JOBCTL_STOP_CONSUME (1UL << JOBCTL_STOP_CONSUME_BIT) @@ -29,6 +33,10 @@ struct task_struct; #define JOBCTL_LISTENING (1UL << JOBCTL_LISTENING_BIT) #define JOBCTL_TRAP_FREEZE (1UL << JOBCTL_TRAP_FREEZE_BIT) +#define JOBCTL_STOPPED (1UL << JOBCTL_STOPPED_BIT) +#define JOBCTL_TRACED (1UL << JOBCTL_TRACED_BIT) +#define JOBCTL_TRACED_FROZEN (1UL << JOBCTL_TRACED_FROZEN_BIT) + #define JOBCTL_TRAP_MASK (JOBCTL_TRAP_STOP | JOBCTL_TRAP_NOTIFY) #define JOBCTL_PENDING_MASK (JOBCTL_STOP_PENDING | JOBCTL_TRAP_MASK) --- a/include/linux/sched/signal.h +++ b/include/linux/sched/signal.h @@ -294,8 +294,10 @@ static inline int kernel_dequeue_signal( static inline void kernel_signal_stop(void) { spin_lock_irq(¤t->sighand->siglock); - if (current->jobctl & JOBCTL_STOP_DEQUEUED) + if (current->jobctl & JOBCTL_STOP_DEQUEUED) { + current->jobctl |= JOBCTL_STOPPED; set_special_state(TASK_STOPPED); + } spin_unlock_irq(¤t->sighand->siglock); schedule(); @@ -437,10 +439,21 @@ extern void signal_wake_up_state(struct static inline void signal_wake_up(struct task_struct *t, bool resume) { + lockdep_assert_held(&t->sighand->siglock); + + if (resume && !(t->jobctl & JOBCTL_TRACED_FROZEN)) + t->jobctl &= ~(JOBCTL_STOPPED | JOBCTL_TRACED); + signal_wake_up_state(t, resume ? TASK_WAKEKILL : 0); } + static inline void ptrace_signal_wake_up(struct task_struct *t, bool resume) { + lockdep_assert_held(&t->sighand->siglock); + + if (resume) + t->jobctl &= ~JOBCTL_TRACED; + signal_wake_up_state(t, resume ? __TASK_TRACED : 0); } --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -185,7 +185,12 @@ static bool looks_like_a_spurious_pid(st return true; } -/* Ensure that nothing can wake it up, even SIGKILL */ +/* + * Ensure that nothing can wake it up, even SIGKILL + * + * A task is switched to this state while a ptrace operation is in progress; + * such that the ptrace operation is uninterruptible. + */ static bool ptrace_freeze_traced(struct task_struct *task) { bool ret = false; @@ -197,6 +202,7 @@ static bool ptrace_freeze_traced(struct spin_lock_irq(&task->sighand->siglock); if (task_is_traced(task) && !looks_like_a_spurious_pid(task) && !__fatal_signal_pending(task)) { + task->jobctl |= JOBCTL_TRACED_FROZEN; WRITE_ONCE(task->__state, __TASK_TRACED); ret = true; } @@ -218,9 +224,11 @@ static void ptrace_unfreeze_traced(struc */ spin_lock_irq(&task->sighand->siglock); if (READ_ONCE(task->__state) == __TASK_TRACED) { - if (__fatal_signal_pending(task)) + task->jobctl &= ~JOBCTL_TRACED_FROZEN; + if (__fatal_signal_pending(task)) { + task->jobctl &= ~JOBCTL_TRACED; wake_up_state(task, __TASK_TRACED); - else + } else WRITE_ONCE(task->__state, TASK_TRACED); } spin_unlock_irq(&task->sighand->siglock); @@ -475,8 +483,10 @@ static int ptrace_attach(struct task_str * in and out of STOPPED are protected by siglock. */ if (task_is_stopped(task) && - task_set_jobctl_pending(task, JOBCTL_TRAP_STOP | JOBCTL_TRAPPING)) + task_set_jobctl_pending(task, JOBCTL_TRAP_STOP | JOBCTL_TRAPPING)) { + task->jobctl &= ~JOBCTL_STOPPED; signal_wake_up_state(task, __TASK_STOPPED); + } spin_unlock(&task->sighand->siglock); --- a/kernel/signal.c +++ b/kernel/signal.c @@ -884,7 +884,7 @@ static int check_kill_permission(int sig static void ptrace_trap_notify(struct task_struct *t) { WARN_ON_ONCE(!(t->ptrace & PT_SEIZED)); - assert_spin_locked(&t->sighand->siglock); + lockdep_assert_held(&t->sighand->siglock); task_set_jobctl_pending(t, JOBCTL_TRAP_NOTIFY); ptrace_signal_wake_up(t, t->jobctl & JOBCTL_LISTENING); @@ -930,9 +930,10 @@ static bool prepare_signal(int sig, stru for_each_thread(p, t) { flush_sigqueue_mask(&flush, &t->pending); task_clear_jobctl_pending(t, JOBCTL_STOP_PENDING); - if (likely(!(t->ptrace & PT_SEIZED))) + if (likely(!(t->ptrace & PT_SEIZED))) { + t->jobctl &= ~JOBCTL_STOPPED; wake_up_state(t, __TASK_STOPPED); - else + } else ptrace_trap_notify(t); } @@ -2219,6 +2220,7 @@ static int ptrace_stop(int exit_code, in * schedule() will not sleep if there is a pending signal that * can awaken the task. */ + current->jobctl |= JOBCTL_TRACED; set_special_state(TASK_TRACED); /* @@ -2460,6 +2462,7 @@ static bool do_signal_stop(int signr) if (task_participate_group_stop(current)) notify = CLD_STOPPED; + current->jobctl |= JOBCTL_STOPPED; set_special_state(TASK_STOPPED); spin_unlock_irq(¤t->sighand->siglock);
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