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

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Message-ID: <20221102102054.30f5adfc@rorschach.local.home>
Date:   Wed, 2 Nov 2022 10:20:54 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Leonid Ravich <leonid.ravich@...anetworks.com>
Cc:     Jason Gunthorpe <jgg@...pe.ca>,
        "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, 2 Nov 2022 14:02:49 +0000
Leonid Ravich <leonid.ravich@...anetworks.com> wrote:

> >I'm guessing some driver's query_pkey op, but AFAIK we don't have any
> >explicit pre-emption reenablements in the code - unless it is sneaky..  
> trace infra uses preempt_disable_notrace/preempt_enable_notrace  to disable/enable preemtion but  my kernel compiled without CONFIG_PREEMPTION so this functions are only barriers - looks like the idea behind was to avoid involuntary preemtion  but in our case it is a voluntary (there is a wait_for_completion in the query_pkey  rabbit hole).
> 
> so no scheduler here to warn about illegal migration. 

Well, you should be testing under different configs ;-)

It would have given you the reason for the real bug.

-- Steve