linux-kernel - Re: kernel BUG at net/rxrpc/local

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Message-ID: <CACT4Y+YVyaTrwpaZfpfi9LKA=5TOdKSL60pjAH04dMPNCZTMSQ@mail.gmail.com>
Date:   Tue, 13 Aug 2019 17:12:24 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     David Howells <dhowells@...hat.com>
Cc:     syzbot <syzbot+1e0edc4b8b7494c28450@...kaller.appspotmail.com>,
        Eric Biggers <ebiggers@...nel.org>,
        David Miller <davem@...emloft.net>,
        linux-afs@...ts.infradead.org, LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: kernel BUG at net/rxrpc/local_object.c:LINE!

On Tue, Aug 13, 2019 at 5:06 PM David Howells <dhowells@...hat.com> wrote:
>
> Dmitry Vyukov <dvyukov@...gle.com> wrote:
>
> > > I meant that I don't know how to turn a tracepoint on from inside the kernel.
> >
> > This /sys/kernel/debug/tracing/events/rxrpc/rxrpc_local/enable in:
> >         echo 1 > /sys/kernel/debug/tracing/events/rxrpc/rxrpc_local/enable
> > should map to some global variable, right? If so, it should be
> > possible to initialize that var to 1 statically. Or that won't work
> > for some reason?
>
> As I understand it, it's all hidden inside of tracing macros and ftrace
> infrastructure and involves runtime patching the code to enable tracepoints
> (they're effectively NOP'ed out when not in use).
>
> So, no, it's not that simple.
>
> I asked Steven and he says:
>
>         trace_set_clr_event("sched", "sched_switch", 1);
>
> is the same as
>
>         echo 1 > events/sched/sched_switch/enable
>
> So it can be done.  Will syzbot actually collect the trace log?

It only collects console output. I don't know what is trace log. If
the trace log is not console output, then it won't.