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Subject[PATCH] sched/fair: Fix null pointer dereference of empty queues
Date
Calling put_prev_task() can result in nr_running being updated
to zero, which would then crash the system when the kernel
attempts to pick_next_entity() with an empty queue.

Signed-off-by: Mohammed Naser <mnaser@vexxhost.com>
---
kernel/sched/fair.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 0d4632f..dd0a74a 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5374,12 +5374,11 @@ again:
simple:
cfs_rq = &rq->cfs;
#endif
+ put_prev_task(rq, prev);

if (!cfs_rq->nr_running)
goto idle;

- put_prev_task(rq, prev);
-
do {
se = pick_next_entity(cfs_rq, NULL);
set_next_entity(cfs_rq, se);
@@ -5415,7 +5414,10 @@ idle:
static void put_prev_task_fair(struct rq *rq, struct task_struct *prev)
{
struct sched_entity *se = &prev->se;
- struct cfs_rq *cfs_rq;
+ struct cfs_rq *cfs_rq = &rq->cfs;
+
+ if (!cfs_rq->nr_running)
+ return;

for_each_sched_entity(se) {
cfs_rq = cfs_rq_of(se);
--
2.3.2 (Apple Git-55)


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