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authorPeter Zijlstra <peterz@infradead.org>2021-02-24 11:42:08 +0100
committerIngo Molnar <mingo@kernel.org>2021-03-06 12:40:21 +0100
commit50caf9c14b1498c90cf808dbba2ca29bd32ccba4 (patch)
tree4cd7d82723c949bb83bcc20eb9d6fe762e1914f2 /kernel
parentsched: Fix affine_move_task() self-concurrency (diff)
downloadlinux-50caf9c14b1498c90cf808dbba2ca29bd32ccba4.tar.xz
linux-50caf9c14b1498c90cf808dbba2ca29bd32ccba4.zip
sched: Simplify set_affinity_pending refcounts
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
Diffstat (limited to 'kernel')
-rw-r--r--kernel/sched/core.c32
1 files changed, 20 insertions, 12 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4e4d100c1f7a..98191218d891 100644
--- 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 *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) {
@@ -2213,7 +2217,7 @@ 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;
}
@@ -2264,9 +2268,9 @@ 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) {
@@ -2282,12 +2286,13 @@ 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);
}
@@ -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;
}