Re: [BUG] possible deadlock in __schedule (with reproducer available)

[Peter Zijlstra]

On Sat, Nov 23, 2024 at 03:39:45AM +0000, Ruan Bonan wrote:

>  </TASK>
> FAULT_INJECTION: forcing a failure.
> name fail_usercopy, interval 1, probability 0, space 0, times 0
> ======================================================
> WARNING: possible circular locking dependency detected
> 6.12.0-rc7-00144-g66418447d27b #8 Not tainted
> ------------------------------------------------------
> syz-executor144/330 is trying to acquire lock:
> ffffffffbcd2da38 ((console_sem).lock){....}-{2:2}, at: down_trylock+0x20/0xa0 kernel/locking/semaphore.c:139
> 
> but task is already holding lock:
> ffff888065cbd718 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested kernel/sched/core.c:598 [inline]
> ffff888065cbd718 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock kernel/sched/sched.h:1506 [inline]
> ffff888065cbd718 (&rq->__lock){-.-.}-{2:2}, at: rq_lock kernel/sched/sched.h:1805 [inline]
> ffff888065cbd718 (&rq->__lock){-.-.}-{2:2}, at: __schedule+0x140/0x1e70 kernel/sched/core.c:6592
> 
> which lock already depends on the new lock.
> 
>        _printk+0x7a/0xa0 kernel/printk/printk.c:2432
>        fail_dump lib/fault-inject.c:46 [inline]
>        should_fail_ex+0x3be/0x570 lib/fault-inject.c:154
>        strncpy_from_user+0x36/0x230 lib/strncpy_from_user.c:118
>        strncpy_from_user_nofault+0x71/0x140 mm/maccess.c:186
>        bpf_probe_read_user_str_common kernel/trace/bpf_trace.c:215 [inline]
>        ____bpf_probe_read_user_str kernel/trace/bpf_trace.c:224 [inline]
>        bpf_probe_read_user_str+0x2a/0x70 kernel/trace/bpf_trace.c:221
>        bpf_prog_bc7c5c6b9645592f+0x3e/0x40
>        bpf_dispatcher_nop_func include/linux/bpf.h:1265 [inline]
>        __bpf_prog_run include/linux/filter.h:701 [inline]
>        bpf_prog_run include/linux/filter.h:708 [inline]
>        __bpf_trace_run kernel/trace/bpf_trace.c:2316 [inline]
>        bpf_trace_run4+0x30b/0x4d0 kernel/trace/bpf_trace.c:2359
>        __bpf_trace_sched_switch+0x1c6/0x2c0 include/trace/events/sched.h:222
>        trace_sched_switch+0x12a/0x190 include/trace/events/sched.h:222

-EWONTFIX. Don't do stupid.