sched/walt: Fix use after free in trace_sched_update_task_ravg()
commit 4d09122c1868 ("sched: Fix spinlock recursion in sched_exit()")
moved freeing of task's current and previous window arrays outside
the rq->lock. These arrays can be accessed from another CPU in parallel
and end up using freed memory. For example,
CPU#0 CPU#1
---------------------------------- -------------------------------
sched_exit() try_to_wake_up()--> The task wakes
up on CPU#0
task_rq_lock() set_task_cpu()
fixup_busy_time() --> waiting for
CPU#0's rq->lock
task_rq_unlock() fixup_busy_time()-->lock acquired
free_task_load_ptrs()
kfree(p->ravg.curr_window_cpu) update_task_ravg()-->called on
current of CPU#0
trace_sched_update_task_ravg()
--> access freed memory
p->ravg.curr_window_cpu = NULL;
To fix this issue, window array pointers must be set to NULL before
freeing the memory. Since this happens outside the lock, memory barriers
are needed on write and read paths. A much simpler alternative would be
skipping update_task_ravg() trace point for tasks that are marked as dead.
The window stats of dead tasks are not updated any ways. While at it, skip
this trace point for newly created tasks for which also window stats are
not updated.
Change-Id: I4d7cb8a3cf7cf84270b09721140d35205643b7ab
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>
1 file changed