From: Andrew Morton <akpm@linux-foundation.org>
To: Shreyas B Prabhu <shreyas@linux.vnet.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
linux-kernel@vger.kernel.org, mingo@redhat.com,
aneesh.kumar@linux.vnet.ibm.com, paulmck@linux.vnet.ibm.com,
preeti@linux.vnet.ibm.com, mgorman@suse.de, namhyung@kernel.org,
lizf@cn.fujitsu.com, acme@redhat.com
Subject: Re: [PATCH RESEND 0/3] tracing/mm: Fix suspicious rcu_dereference_check() usage warnings
Date: Thu, 14 May 2015 13:08:23 -0700 [thread overview]
Message-ID: <20150514130823.4502e151e0e31321a114edcd@linux-foundation.org> (raw)
In-Reply-To: <5553017A.2080905@linux.vnet.ibm.com>
On Wed, 13 May 2015 13:17:06 +0530 Shreyas B Prabhu <shreyas@linux.vnet.ibm.com> wrote:
> >>> + TP_CONDITION(cpu_online(smp_processor_id())),
> >>
> >> Are we sure these can't generate check_preemption_disabled() warnings?
> >> Is there some reason why all these calls always occur with preemption
> >> disabled?
> >
> > Good catch. I don't think the code does.
> >
> > Now, I'm not sure if we should just add a raw_smp_processor_id(). The
> > idea is just to make sure that the CPU we are running on is online,
> > because it is possible to call theses trace points when the CPU is
> > going offline. If that happens, then there's a race with RCU.
> >
> > Since a task can not be migrated to an offline CPU, we don't need to
> > worry about the cpu_online(smp_processor_id()) returning a false
> > positive. A false negative would just skip a tracepoint, but I'm not
> > sure that is possible either.
> >
> > In any case, comments should also be added to why the condition is
> > there.
> >
> I'll send a patch adding the comments.
Please also confirm that these tracepoints cannot be called
from preemptible contexts. Or switch to raw_smp_processor_id().
next prev parent reply other threads:[~2015-05-14 20:08 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-08 17:20 [PATCH RESEND 0/3] tracing/mm: Fix suspicious rcu_dereference_check() usage warnings Shreyas B. Prabhu
2015-05-08 17:20 ` [PATCH RESEND 1/3] tracing/mm: Don't trace kmem_cache_free on offline cpus Shreyas B. Prabhu
2015-05-08 17:20 ` [PATCH RESEND 2/3] tracing/mm: Don't trace mm_page_free " Shreyas B. Prabhu
2015-05-08 17:20 ` [PATCH RESEND 3/3] tracing/mm: Don't trace mm_page_pcpu_drain " Shreyas B. Prabhu
2015-05-12 7:29 ` [PATCH RESEND 0/3] tracing/mm: Fix suspicious rcu_dereference_check() usage warnings Shreyas B Prabhu
2015-05-12 20:03 ` Steven Rostedt
2015-05-12 20:36 ` Andrew Morton
2015-05-12 20:54 ` Steven Rostedt
2015-05-13 7:47 ` Shreyas B Prabhu
2015-05-14 20:08 ` Andrew Morton [this message]
2015-05-14 20:38 ` Steven Rostedt
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