linux-kernel - Re: [PATCH] kallsyms: Fix scheduling with interrupts disabled in self-test

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Date:   Fri, 13 Jan 2023 09:44:35 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     Nicholas Piggin <npiggin@...il.com>,
        Zhen Lei <thunder.leizhen@...wei.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, "Erhard F ." <erhard_f@...lbox.org>,
        kernel test robot <oliver.sang@...el.com>
Subject: Re: [PATCH] kallsyms: Fix scheduling with interrupts disabled in
 self-test

On Thu 2023-01-12 10:24:43, Luis Chamberlain wrote:
> On Thu, Jan 12, 2023 at 08:54:26PM +1000, Nicholas Piggin wrote:
> > kallsyms_on_each* may schedule so must not be called with interrupts
> > disabled. The iteration function could disable interrupts, but this
> > also changes lookup_symbol() to match the change to the other timing
> > code.
> > 
> > Reported-by: Erhard F. <erhard_f@...lbox.org>
> > Link: https://lore.kernel.org/all/bug-216902-206035@https.bugzilla.kernel.org%2F/
> > Reported-by: kernel test robot <oliver.sang@...el.com>
> > Link: https://lore.kernel.org/oe-lkp/202212251728.8d0872ff-oliver.sang@intel.com
> > Fixes: 30f3bb09778d ("kallsyms: Add self-test facility")
> > Signed-off-by: Nicholas Piggin <npiggin@...il.com>
> > ---
> 
> Thanks Nicholas!
> 
> Petr had just suggested removing this aspect of the selftests, the performance
> test as its specific to the config, it doesn't run many times to get an
> average and odd things on a system can create different metrics. Zhen Lei
> had given up on fixing it and has a patch to instead remove this part of
> the selftest.
> 
> I still find value in keeping it, but Petr, would like your opinion on
> this fix, if we were to keep it.

I am fine with this fix.

It increases a risk of possible inaccuracy of the measured time.
It would count also time spent on unrelated interrupts and eventual
rescheduling.

Anyway, it is safe at least. I was against the previous attempts to
fix this problem because they might have caused problems for
the rest of the system.

Best Regards,
Petr