[<prev] [next>] [thread-next>] [day] [month] [year] [list]
Message-ID: <20250904125522.561737-1-arighi@nvidia.com>
Date: Thu, 4 Sep 2025 14:55:22 +0200
From: Andrea Righi <arighi@...dia.com>
To: Tejun Heo <tj@...nel.org>,
David Vernet <void@...ifault.com>,
Changwoo Min <changwoo@...lia.com>
Cc: Christian Loehle <christian.loehle@....com>,
Jake Hillion <jakehillion@...a.com>,
sched-ext@...ts.linux.dev,
linux-kernel@...r.kernel.org
Subject: [PATCH sched_ext/for-6.18] sched_ext: Fix NULL dereference in scx_bpf_cpu_rq() warning
When printing the deprecation warning for scx_bpf_cpu_rq(), we may hit a
NULL pointer dereference if the kfunc is called before a BPF scheduler
is fully attached, for example, when invoked from a BPF timer or during
ops.init():
[ 50.752775] BUG: kernel NULL pointer dereference, address: 0000000000000331
...
[ 50.764205] RIP: 0010:scx_bpf_cpu_rq+0x30/0xa0
...
[ 50.787661] Call Trace:
[ 50.788398] <TASK>
[ 50.789061] bpf_prog_08f7fd2dcb187aaf_wakeup_timerfn+0x75/0x1a8
[ 50.792477] bpf_timer_cb+0x7e/0x140
[ 50.796003] hrtimer_run_softirq+0x91/0xe0
[ 50.796952] handle_softirqs+0xce/0x3c0
[ 50.799087] run_ksoftirqd+0x3e/0x70
[ 50.800197] smpboot_thread_fn+0x133/0x290
[ 50.802320] kthread+0x115/0x220
[ 50.804984] ret_from_fork+0x17a/0x1d0
[ 50.806920] ret_from_fork_asm+0x1a/0x30
[ 50.807799] </TASK>
Fix this by only printing the warning once the scheduler is fully
registered.
Fixes: 5c48d88fe0049 ("sched_ext: deprecation warn for scx_bpf_cpu_rq()")
Cc: Christian Loehle <christian.loehle@....com>
Signed-off-by: Andrea Righi <arighi@...dia.com>
---
kernel/sched/ext.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 489462290142a..04fefd34db238 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -6362,17 +6362,20 @@ __bpf_kfunc s32 scx_bpf_task_cpu(const struct task_struct *p)
*/
__bpf_kfunc struct rq *scx_bpf_cpu_rq(s32 cpu)
{
- struct scx_sched *sch = scx_root;
+ struct scx_sched *sch;
if (!kf_cpu_valid(cpu, NULL))
return NULL;
- if (!sch->warned_deprecated_rq) {
+ rcu_read_lock();
+ sch = rcu_dereference(scx_root);
+ if (sch && sch->warned_deprecated_rq) {
printk_deferred(KERN_WARNING "sched_ext: %s() is deprecated; "
"use scx_bpf_locked_rq() when holding rq lock "
"or scx_bpf_cpu_curr() to read remote curr safely.\n", __func__);
sch->warned_deprecated_rq = true;
}
+ rcu_read_unlock();
return cpu_rq(cpu);
}
--
2.51.0
Powered by blists - more mailing lists