From 6681b566fe9ffe9365121a790537ada2e4ef97ba Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Tue, 8 Jun 2021 00:37:35 -0400 Subject: [PATCH 294/323] sched: Simplify set_affinity_pending refcounts Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.10/older/patches-5.10.204-rt100.tar.xz commit 50caf9c14b1498c90cf808dbba2ca29bd32ccba4 upstream. Now that we have set_affinity_pending::stop_pending to indicate if a stopper is in progress, and we have the guarantee that if that stopper exists, it will (eventually) complete our @pending we can simplify the refcount scheme by no longer counting the stopper thread. Fixes: 6d337eab041d ("sched: Fix migrate_disable() vs set_cpus_allowed_ptr()") Cc: stable@kernel.org Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Reviewed-by: Valentin Schneider Link: https://lkml.kernel.org/r/20210224131355.724130207@infradead.org Signed-off-by: Paul Gortmaker Signed-off-by: Steven Rostedt (VMware) --- kernel/sched/core.c | 32 ++++++++++++++++++++------------ 1 file changed, 20 insertions(+), 12 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 76fa3daf1f60..d3b9d69171a2 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1914,6 +1914,10 @@ struct migration_arg { struct set_affinity_pending *pending; }; +/* + * @refs: number of wait_for_completion() + * @stop_pending: is @stop_work in use + */ struct set_affinity_pending { refcount_t refs; unsigned int stop_pending; @@ -2049,10 +2053,6 @@ static int migration_cpu_stop(void *data) if (complete) complete_all(&pending->done); - /* For pending->{arg,stop_work} */ - if (pending && refcount_dec_and_test(&pending->refs)) - wake_up_var(&pending->refs); - return 0; } @@ -2251,12 +2251,16 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag push_task = get_task_struct(p); } + /* + * If there are pending waiters, but no pending stop_work, + * then complete now. + */ pending = p->migration_pending; - if (pending) { - refcount_inc(&pending->refs); + if (pending && !pending->stop_pending) { p->migration_pending = NULL; complete = true; } + task_rq_unlock(rq, p, rf); if (push_task) { @@ -2265,7 +2269,7 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag } if (complete) - goto do_complete; + complete_all(&pending->done); return 0; } @@ -2316,9 +2320,9 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag if (!stop_pending) pending->stop_pending = true; - refcount_inc(&pending->refs); /* pending->{arg,stop_work} */ if (flags & SCA_MIGRATE_ENABLE) p->migration_flags &= ~MDF_PUSH; + task_rq_unlock(rq, p, rf); if (!stop_pending) { @@ -2334,12 +2338,13 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag if (task_on_rq_queued(p)) rq = move_queued_task(rq, rf, p, dest_cpu); - p->migration_pending = NULL; - complete = true; + if (!pending->stop_pending) { + p->migration_pending = NULL; + complete = true; + } } task_rq_unlock(rq, p, rf); -do_complete: if (complete) complete_all(&pending->done); } @@ -2347,7 +2352,7 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag wait_for_completion(&pending->done); if (refcount_dec_and_test(&pending->refs)) - wake_up_var(&pending->refs); + wake_up_var(&pending->refs); /* No UaF, just an address */ /* * Block the original owner of &pending until all subsequent callers @@ -2355,6 +2360,9 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag */ wait_var_event(&my_pending.refs, !refcount_read(&my_pending.refs)); + /* ARGH */ + WARN_ON_ONCE(my_pending.stop_pending); + return 0; } -- 2.43.0