bpf_free_inode() is invoked as a RCU callback. Usually RCU callbacks are
invoked within softirq context. By setting rcutree.use_softirq=0 boot
option the RCU callbacks will be invoked in a per-CPU kthread with
bottom halves disabled which implies a RCU read section.
On PREEMPT_RT the context remains fully preemptible. The RCU read
section however does not allow schedule() invocation. The latter happens
in mutex_lock() performed by bpf_trampoline_unlink_prog() originated
from bpf_link_put().
Remove the context checks and use the workqueue unconditionally.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
---
The warning can be observed as:
| BUG: sleeping function called from invalid context at kernel/locking/rtmutex_api.c:510
| in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid: 47, name: rcuc/3
| preempt_count: 0, expected: 0
| RCU nest depth: 2, expected: 0
| CPU: 3 PID: 47 Comm: rcuc/3 Tainted: G E v6.3-rt12 #1
| Hardware name: Supermicro X9SCL/X9SCM/X9SCL/X9SCM, BIOS 2.3a 01/06/2021
| Call Trace:
| <TASK>
| dump_stack_lvl+0x43/0x60
| __might_resched+0x137/0x190
| mutex_lock+0x1a/0x50
| bpf_trampoline_unlink_prog+0x1b/0x100
| bpf_tracing_link_release+0x12/0x40
| bpf_link_free+0x70/0x90
| bpf_free_inode+0x3e/0x80
| rcu_core+0x4ff/0x7c0
| rcu_cpu_kthread+0xa9/0x2f0
| smpboot_thread_fn+0x141/0x2c0
| kthread+0x110/0x130
| ret_from_fork+0x2c/0x50
| </TASK>
kernel/bpf/syscall.c | 8 ++------
1 file changed, 2 insertions(+), 6 deletions(-)
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 14f39c1e573ee..0adaa1bfbb0d2 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2785,12 +2785,8 @@ void bpf_link_put(struct bpf_link *link)
if (!atomic64_dec_and_test(&link->refcnt))
return;
- if (in_atomic()) {
- INIT_WORK(&link->work, bpf_link_put_deferred);
- schedule_work(&link->work);
- } else {
- bpf_link_free(link);
- }
+ INIT_WORK(&link->work, bpf_link_put_deferred);
+ schedule_work(&link->work);
}
EXPORT_SYMBOL(bpf_link_put);
--
2.40.1
