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

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Message-ID: <Y2LMjYNAE5LwtcOp@leonid-Inspiron-3421>
Date:   Wed, 2 Nov 2022 22:01:17 +0200
From:   Leonid Ravich <lravich@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Jason Gunthorpe <jgg@...pe.ca>,
        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>
Subject: Re: BUG:  ib_mad ftrace event unsupported migration

> 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.
>

disagree, without CONFIG_PREEMPTION (which is the default case in some
destros) we will not get any warning, because there will not be
preamption disable.

second issue I see and maybe it is only me, is that the assuption of
atomicity in trace is not a common knowledge for trace users.