On 2024-06-26, Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> wrote:
> On 2024/06/25 23:17, John Ogness wrote:
>> On 2024-06-25, Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> wrote:
>>> syzbot is reporting circular locking dependency inside __bpf_prog_run(),
>>> for fault injection calls printk() despite rq lock is already held.
>>>
>>> Guard __bpf_prog_run() using printk_deferred_{enter,exit}() (and
>>> preempt_{disable,enable}() if CONFIG_PREEMPT_RT=n) in order to defer any
>>> printk() messages.
>>
>> Why is the reason for disabling preemption?
>
> Because since kernel/printk/printk_safe.c uses a percpu counter for deferring
> printk(), printk_safe_enter() and printk_safe_exit() have to be called from
> the same CPU. preempt_disable() before printk_safe_enter() and preempt_enable()
> after printk_safe_exit() guarantees that printk_safe_enter() and
> printk_safe_exit() are called from the same CPU.
Yes, but we already have cant_migrate(). Are you suggesting there are
configurations where cant_migrate() is true but the context can be
migrated anyway?
John
