linux-kernel - Re: BUG: ib_mad ftrace event unsupported migration

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Date:   Wed, 2 Nov 2022 13:01:20 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Leonid Ravich <leonid.ravich@...anetworks.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Yigal Korman <yigal.korman@...anetworks.com>,
        "linux-trace-kernel@...r.kernel.org" 
        <linux-trace-kernel@...r.kernel.org>,
        Leon Ravich <lravich@...il.com>
Subject: Re: BUG:  ib_mad ftrace event unsupported migration

On Wed, Nov 02, 2022 at 11:59:47AM -0400, Steven Rostedt wrote:
> On Wed, 2 Nov 2022 11:24:20 -0300
> Jason Gunthorpe <jgg@...pe.ca> wrote:
> 
> > No, it doesn't muck with preemption, it will have some sleeping lock,
> > eg mlx5_ib_query_pkey() does a memory allocation as the first thing
> > 
> > It seems like a bug that calling kmalloc(GFP_KERNEL)/might_sleep()
> > from within a tracepoint doesn't trigger a warning?
> 
> Has nothing to do with tracepoints. You could call it a bug that it
> doesn't trigger a warning when preemption is disabled. But then again,
> it would if you enabled DEBUG_PREEMPT and possibly LOCKDEP too. So, I chalk
> this up to a lack of proper testing.

That makes sense, assuming it does trigger in those cases.

It is interesting nobody has run those tracepoints on a debug kernel.

Jason