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    Subject[PATCH 9/9] ptrace: Don't change __state
    Stop playing with tsk->__state to remove TASK_WAKEKILL while a ptrace
    command is executing.

    Instead implement a new jobtl flag JOBCTL_DELAY_WAKEKILL. This new
    flag is set in jobctl_freeze_task and cleared when ptrace_stop is
    awoken or in jobctl_unfreeze_task (when ptrace_stop remains asleep).

    In signal_wake_up_state drop TASK_WAKEKILL from state if TASK_WAKEKILL
    is used while JOBCTL_DELAY_WAKEKILL is set. This has the same effect
    as changing TASK_TRACED to __TASK_TRACED as all of the wake_ups that
    use TASK_KILLABLE go through signal_wake_up except the wake_up in
    ptrace_unfreeze_traced.

    Previously the __state value of __TASK_TRACED was changed to
    TASK_RUNNING when woken up or back to TASK_TRACED when the code was
    left in ptrace_stop. Now when woken up ptrace_stop now clears
    JOBCTL_DELAY_WAKEKILL and when left sleeping ptrace_unfreezed_traced
    clears JOBCTL_DELAY_WAKEKILL.

    Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
    ---
    include/linux/sched/jobctl.h | 2 ++
    include/linux/sched/signal.h | 3 ++-
    kernel/ptrace.c | 11 +++++------
    kernel/signal.c | 1 +
    4 files changed, 10 insertions(+), 7 deletions(-)

    diff --git a/include/linux/sched/jobctl.h b/include/linux/sched/jobctl.h
    index fa067de9f1a9..4e154ad8205f 100644
    --- a/include/linux/sched/jobctl.h
    +++ b/include/linux/sched/jobctl.h
    @@ -19,6 +19,7 @@ struct task_struct;
    #define JOBCTL_TRAPPING_BIT 21 /* switching to TRACED */
    #define JOBCTL_LISTENING_BIT 22 /* ptracer is listening for events */
    #define JOBCTL_TRAP_FREEZE_BIT 23 /* trap for cgroup freezer */
    +#define JOBCTL_DELAY_WAKEKILL_BIT 24 /* delay killable wakeups */

    #define JOBCTL_STOP_DEQUEUED (1UL << JOBCTL_STOP_DEQUEUED_BIT)
    #define JOBCTL_STOP_PENDING (1UL << JOBCTL_STOP_PENDING_BIT)
    @@ -28,6 +29,7 @@ struct task_struct;
    #define JOBCTL_TRAPPING (1UL << JOBCTL_TRAPPING_BIT)
    #define JOBCTL_LISTENING (1UL << JOBCTL_LISTENING_BIT)
    #define JOBCTL_TRAP_FREEZE (1UL << JOBCTL_TRAP_FREEZE_BIT)
    +#define JOBCTL_DELAY_WAKEKILL (1UL << JOBCTL_DELAY_WAKEKILL_BIT)

    #define JOBCTL_TRAP_MASK (JOBCTL_TRAP_STOP | JOBCTL_TRAP_NOTIFY)
    #define JOBCTL_PENDING_MASK (JOBCTL_STOP_PENDING | JOBCTL_TRAP_MASK)
    diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
    index 3c8b34876744..1947c85aa9d9 100644
    --- a/include/linux/sched/signal.h
    +++ b/include/linux/sched/signal.h
    @@ -437,7 +437,8 @@ extern void signal_wake_up_state(struct task_struct *t, unsigned int state);

    static inline void signal_wake_up(struct task_struct *t, bool resume)
    {
    - signal_wake_up_state(t, resume ? TASK_WAKEKILL : 0);
    + bool wakekill = resume && !(t->jobctl & JOBCTL_DELAY_WAKEKILL);
    + signal_wake_up_state(t, wakekill ? TASK_WAKEKILL : 0);
    }
    static inline void ptrace_signal_wake_up(struct task_struct *t, bool resume)
    {
    diff --git a/kernel/ptrace.c b/kernel/ptrace.c
    index 842511ee9a9f..0bea74539320 100644
    --- a/kernel/ptrace.c
    +++ b/kernel/ptrace.c
    @@ -194,7 +194,7 @@ static bool ptrace_freeze_traced(struct task_struct *task)

    if (task_is_traced(task) && !looks_like_a_spurious_pid(task) &&
    !__fatal_signal_pending(task)) {
    - WRITE_ONCE(task->__state, __TASK_TRACED);
    + task->jobctl |= JOBCTL_DELAY_WAKEKILL;
    ret = true;
    }

    @@ -203,7 +203,7 @@ static bool ptrace_freeze_traced(struct task_struct *task)

    static void ptrace_unfreeze_traced(struct task_struct *task)
    {
    - if (READ_ONCE(task->__state) != __TASK_TRACED)
    + if (!(READ_ONCE(task->jobctl) & JOBCTL_DELAY_WAKEKILL))
    return;

    WARN_ON(!task->ptrace || task->parent != current);
    @@ -213,11 +213,10 @@ static void ptrace_unfreeze_traced(struct task_struct *task)
    * Recheck state under the lock to close this race.
    */
    spin_lock_irq(&task->sighand->siglock);
    - if (READ_ONCE(task->__state) == __TASK_TRACED) {
    + if (task->jobctl & JOBCTL_DELAY_WAKEKILL) {
    + task->jobctl &= ~JOBCTL_DELAY_WAKEKILL;
    if (__fatal_signal_pending(task))
    wake_up_state(task, __TASK_TRACED);
    - else
    - WRITE_ONCE(task->__state, TASK_TRACED);
    }
    spin_unlock_irq(&task->sighand->siglock);
    }
    @@ -253,7 +252,7 @@ static int ptrace_check_attach(struct task_struct *child, bool ignore_state)
    */
    if (lock_task_sighand(child, &flags)) {
    if (child->ptrace && child->parent == current) {
    - WARN_ON(READ_ONCE(child->__state) == __TASK_TRACED);
    + WARN_ON(child->jobctl & JOBCTL_DELAY_WAKEKILL);
    /*
    * child->sighand can't be NULL, release_task()
    * does ptrace_unlink() before __exit_signal().
    diff --git a/kernel/signal.c b/kernel/signal.c
    index 584d67deb3cb..2b332f89cbad 100644
    --- a/kernel/signal.c
    +++ b/kernel/signal.c
    @@ -2307,6 +2307,7 @@ static int ptrace_stop(int exit_code, int why, int clear_code,

    /* LISTENING can be set only during STOP traps, clear it */
    current->jobctl &= ~JOBCTL_LISTENING;
    + current->jobctl &= ~JOBCTL_DELAY_WAKEKILL;

    /*
    * Queued signals ignored us while we were stopped for tracing.
    --
    2.35.3
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