Messages in this thread Patch in this message | | | Date | Wed, 7 Sep 2022 11:30:53 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v3 3/6] sched: Change wait_task_inactive()s match_state |
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On Tue, Sep 06, 2022 at 12:54:34PM +0200, Peter Zijlstra wrote:
> > Suggestion #3: > > > > - Couldn't the following users with a 0 mask: > > > > drivers/powercap/idle_inject.c: wait_task_inactive(iit->tsk, 0); > > fs/coredump.c: wait_task_inactive(ptr->task, 0); > > > > Use ~0 instead (exposed as TASK_ANY or so) and then we can drop the > > !match_state special case? > > > > They'd do something like: > > > > drivers/powercap/idle_inject.c: wait_task_inactive(iit->tsk, TASK_ANY); > > fs/coredump.c: wait_task_inactive(ptr->task, TASK_ANY); > > > > It's not an entirely 100% equivalent transformation though, but looks OK > > at first sight: ->__state will be some nonzero mask for genuine tasks > > waiting to schedule out, so any match will be functionally the same as a > > 0 flag telling us not to check any of the bits, right? I might be missing > > something though. > > I too am thinking that should work. Added patch for that.
--- Subject: sched: Add TASK_ANY for wait_task_inactive() From: Peter Zijlstra <peterz@infradead.org> Date: Tue Sep 6 12:39:55 CEST 2022
Now that wait_task_inactive()'s @match_state argument is a mask (like ttwu()) it is possible to replace the special !match_state case with an 'all-states' value such that any blocked state will match.
Suggested-by: Ingo Molnar (mingo@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- drivers/powercap/idle_inject.c | 2 +- fs/coredump.c | 2 +- include/linux/sched.h | 2 ++ kernel/sched/core.c | 16 ++++++++-------- 4 files changed, 12 insertions(+), 10 deletions(-)
--- a/drivers/powercap/idle_inject.c +++ b/drivers/powercap/idle_inject.c @@ -254,7 +254,7 @@ void idle_inject_stop(struct idle_inject iit = per_cpu_ptr(&idle_inject_thread, cpu); iit->should_run = 0; - wait_task_inactive(iit->tsk, 0); + wait_task_inactive(iit->tsk, TASK_ANY); } cpu_hotplug_enable(); --- a/fs/coredump.c +++ b/fs/coredump.c @@ -412,7 +412,7 @@ static int coredump_wait(int exit_code, */ ptr = core_state->dumper.next; while (ptr != NULL) { - wait_task_inactive(ptr->task, 0); + wait_task_inactive(ptr->task, TASK_ANY); ptr = ptr->next; } } --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -101,6 +101,8 @@ struct task_group; #define TASK_RTLOCK_WAIT 0x1000 #define TASK_STATE_MAX 0x2000 +#define TASK_ANY (TASK_STATE_MAX-1) + /* Convenience macros for the sake of set_current_state: */ #define TASK_KILLABLE (TASK_WAKEKILL | TASK_UNINTERRUPTIBLE) #define TASK_STOPPED (TASK_WAKEKILL | __TASK_STOPPED) --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3254,12 +3254,12 @@ int migrate_swap(struct task_struct *cur /* * wait_task_inactive - wait for a thread to unschedule. * - * If @match_state is nonzero, it's the @p->state value just checked and - * not expected to change. If it changes, i.e. @p might have woken up, - * then return zero. When we succeed in waiting for @p to be off its CPU, - * we return a positive number (its total switch count). If a second call - * a short while later returns the same number, the caller can be sure that - * @p has remained unscheduled the whole time. + * Wait for the thread to block in any of the states set in @match_state. + * If it changes, i.e. @p might have woken up, then return zero. When we + * succeed in waiting for @p to be off its CPU, we return a positive number + * (its total switch count). If a second call a short while later returns the + * same number, the caller can be sure that @p has remained unscheduled the + * whole time. * * The caller must ensure that the task *will* unschedule sometime soon, * else this function might spin for a *long* time. This function can't @@ -3295,7 +3295,7 @@ unsigned long wait_task_inactive(struct * is actually now running somewhere else! */ while (task_on_cpu(rq, p)) { - if (match_state && !(READ_ONCE(p->__state) & match_state)) + if (!(READ_ONCE(p->__state) & match_state)) return 0; cpu_relax(); } @@ -3310,7 +3310,7 @@ unsigned long wait_task_inactive(struct running = task_on_cpu(rq, p); queued = task_on_rq_queued(p); ncsw = 0; - if (!match_state || (READ_ONCE(p->__state) & match_state)) + if (READ_ONCE(p->__state) & match_state) ncsw = p->nvcsw | LONG_MIN; /* sets MSB */ task_rq_unlock(rq, p, &rf);
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