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Message-Id: <20210315135517.065144356@linuxfoundation.org>
Date: Mon, 15 Mar 2021 14:55:41 +0100
From: gregkh@...uxfoundation.org
To: linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
stable@...r.kernel.org, stable@...nel.org,
"Peter Zijlstra (Intel)" <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>,
Valentin Schneider <valentin.schneider@....com>
Subject: [PATCH 5.11 278/306] sched: Simplify set_affinity_pending refcounts
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
From: Peter Zijlstra <peterz@...radead.org>
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@...nel.org
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Reviewed-by: Valentin Schneider <valentin.schneider@....com>
Link: https://lkml.kernel.org/r/20210224131355.724130207@infradead.org
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
kernel/sched/core.c | 32 ++++++++++++++++++++------------
1 file changed, 20 insertions(+), 12 deletions(-)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1862,6 +1862,10 @@ 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;
@@ -1997,10 +2001,6 @@ out:
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;
}
@@ -2199,12 +2199,16 @@ static int affine_move_task(struct rq *r
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) {
@@ -2213,7 +2217,7 @@ static int affine_move_task(struct rq *r
}
if (complete)
- goto do_complete;
+ complete_all(&pending->done);
return 0;
}
@@ -2264,9 +2268,9 @@ static int affine_move_task(struct rq *r
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) {
@@ -2282,12 +2286,13 @@ static int affine_move_task(struct rq *r
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);
}
@@ -2295,7 +2300,7 @@ do_complete:
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
@@ -2303,6 +2308,9 @@ do_complete:
*/
wait_var_event(&my_pending.refs, !refcount_read(&my_pending.refs));
+ /* ARGH */
+ WARN_ON_ONCE(my_pending.stop_pending);
+
return 0;
}
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