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From 6681b566fe9ffe9365121a790537ada2e4ef97ba Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@infradead.org>
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) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Link: https://lkml.kernel.org/r/20210224131355.724130207@infradead.org
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
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
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