This is a note to let you know that I've just added the patch titled
sched/deadline: Fix task_struct reference leak
to the 6.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
sched-deadline-fix-task_struct-reference-leak.patch
and it can be found in the queue-6.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 9b637a8fa893a2b891c492dee16e577fc166ad1a
Author: Wander Lairson Costa <wander@xxxxxxxxxx>
Date: Thu Jun 20 09:56:17 2024 -0300
sched/deadline: Fix task_struct reference leak
[ Upstream commit b58652db66c910c2245f5bee7deca41c12d707b9 ]
During the execution of the following stress test with linux-rt:
stress-ng --cyclic 30 --timeout 30 --minimize --quiet
kmemleak frequently reported a memory leak concerning the task_struct:
unreferenced object 0xffff8881305b8000 (size 16136):
comm "stress-ng", pid 614, jiffies 4294883961 (age 286.412s)
object hex dump (first 32 bytes):
02 40 00 00 00 00 00 00 00 00 00 00 00 00 00 00 .@..............
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
debug hex dump (first 16 bytes):
53 09 00 00 00 00 00 00 00 00 00 00 00 00 00 00 S...............
backtrace:
[<00000000046b6790>] dup_task_struct+0x30/0x540
[<00000000c5ca0f0b>] copy_process+0x3d9/0x50e0
[<00000000ced59777>] kernel_clone+0xb0/0x770
[<00000000a50befdc>] __do_sys_clone+0xb6/0xf0
[<000000001dbf2008>] do_syscall_64+0x5d/0xf0
[<00000000552900ff>] entry_SYSCALL_64_after_hwframe+0x6e/0x76
The issue occurs in start_dl_timer(), which increments the task_struct
reference count and sets a timer. The timer callback, dl_task_timer,
is supposed to decrement the reference count upon expiration. However,
if enqueue_task_dl() is called before the timer expires and cancels it,
the reference count is not decremented, leading to the leak.
This patch fixes the reference leak by ensuring the task_struct
reference count is properly decremented when the timer is canceled.
Fixes: feff2e65efd8 ("sched/deadline: Unthrottle PI boosted threads while enqueuing")
Signed-off-by: Wander Lairson Costa <wander@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Acked-by: Juri Lelli <juri.lelli@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20240620125618.11419-1-wander@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index a04a436af8cc4..dce51bf2d3229 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1805,8 +1805,13 @@ static void enqueue_task_dl(struct rq *rq, struct task_struct *p, int flags)
* The replenish timer needs to be canceled. No
* problem if it fires concurrently: boosted threads
* are ignored in dl_task_timer().
+ *
+ * If the timer callback was running (hrtimer_try_to_cancel == -1),
+ * it will eventually call put_task_struct().
*/
- hrtimer_try_to_cancel(&p->dl.dl_timer);
+ if (hrtimer_try_to_cancel(&p->dl.dl_timer) == 1 &&
+ !dl_server(&p->dl))
+ put_task_struct(p);
p->dl.dl_throttled = 0;
}
} else if (!dl_prio(p->normal_prio)) {
