From: Aaron Tomlin <atomlin@redhat.com>
To: Luis Chamberlain <mcgrof@kernel.org>
Cc: rostedt@goodmis.org, cl@linux.com, pmladek@suse.com,
mbenes@suse.cz, christophe.leroy@csgroup.eu,
akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
linux-modules@vger.kernel.org, atomlin@atomlin.com,
ghalat@redhat.com, oleksandr@natalenko.name, neelx@redhat.com,
daniel.thompson@linaro.org, hch@infradead.org,
tglx@linutronix.de, linux-rt-users@vger.kernel.org
Subject: Re: [PATCH v2] module: kallsyms: Ensure preemption in add_kallsyms() with PREEMPT_RT
Date: Thu, 7 Jul 2022 17:57:50 +0100 [thread overview]
Message-ID: <20220707165750.tk4fadpv3d4zr2mb@ava.usersys.com> (raw)
In-Reply-To: <YsXNVSAtO+VDggcI@bombadil.infradead.org>
On Wed 2022-07-06 10:58 -0700, Luis Chamberlain wrote:
> Hey Aaron, thanks again!
Hi Luis,
No problem :)
> On Mon, Jul 04, 2022 at 05:17:53PM +0100, Aaron Tomlin wrote:
> > To disable preemption in the context of add_kallsyms() is incorrect.
>
> Why, what broke? Did this used to work? Was the commit in question a
> regression then? Clarifying all this will help a lot.
Sorry for the confusion! If I understand correctly, nothing broke
intrinsically.
Rather with commit 08126db5ff73 ("module: kallsyms: Fix suspicious rcu
usage") under PREEMPT_RT=y, by disabling preemption, I introduced an
unbounded latency since the loop is not fixed which is generally frowned
upon. So, I would say this was a regression since earlier preemption was
not disabled and we would dereference RCU-protected pointers explicitly
i.e. without using the more appropriate rcu_dereference() family
of primitives. That being said, these pointers cannot change in this
context as explained previously.
Would the above be suitable - just to confirm before I send another
iteration?
Kind regards,
--
Aaron Tomlin
next prev parent reply other threads:[~2022-07-07 16:58 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-04 16:17 Aaron Tomlin
2022-07-06 17:58 ` Luis Chamberlain
2022-07-07 16:57 ` Aaron Tomlin [this message]
2022-07-07 17:20 ` Luis Chamberlain
2022-07-07 18:56 ` Aaron Tomlin
2022-07-11 15:57 ` Luis Chamberlain
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