6.9-stable review patch. If anyone has any objections, please let me know.
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From: Wander Lairson Costa wander@redhat.com
[ 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@redhat.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Acked-by: Juri Lelli juri.lelli@redhat.com Link: https://lore.kernel.org/r/20240620125618.11419-1-wander@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/sched/deadline.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
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)) {