Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Thu, 30 Apr 2020 12:18:22 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To:     rostedt <rostedt@goodmis.org>
Cc:     Joerg Roedel <jroedel@suse.de>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Borislav Petkov <bp@alien8.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Shile Zhang <shile.zhang@linux.alibaba.com>,
        Andy Lutomirski <luto@amacapital.net>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Tzvetomir Stoyanov <tz.stoyanov@gmail.com>
Message-ID: <947455570.77870.1588263502669.JavaMail.zimbra@efficios.com>
In-Reply-To: <20200430121627.682061e2@gandalf.local.home>
References: <20200429054857.66e8e333@oasis.local.home> <20200429105941.GQ30814@suse.de> <20200429082854.6e1796b5@oasis.local.home> <20200429100731.201312a9@gandalf.local.home> <20200430141120.GA8135@suse.de> <20200430145057.GB8135@suse.de> <2026887875.77814.1588260015439.JavaMail.zimbra@efficios.com> <20200430121627.682061e2@gandalf.local.home>
Subject: Re: [RFC][PATCH] x86/mm: Sync all vmalloc mappings before
 text_poke()
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit
Thread-Topic: x86/mm: Sync all vmalloc mappings before text_poke()
Thread-Index: rw6BtFhk9xaOWvTrQYsbm6qr+yaRNA==
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

----- On Apr 30, 2020, at 12:16 PM, rostedt rostedt@goodmis.org wrote:

> On Thu, 30 Apr 2020 11:20:15 -0400 (EDT)
> Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote:
> 
>> > The right fix is to call vmalloc_sync_mappings() right after allocating
>> > tracing or perf buffers via v[zm]alloc().
>> 
>> Either right after allocation, or right before making the vmalloc'd data
>> structure visible to the instrumentation. In the case of the pid filter,
>> that would be the rcu_assign_pointer() which publishes the new pid filter
>> table.
>> 
>> As long as vmalloc_sync_mappings() is performed somewhere *between* allocation
>> and publishing the pointer for instrumentation, it's fine.
>> 
>> I'll let Steven decide on which approach works best for him.
> 
> As stated in the other email, I don't see it having anything to do with
> vmalloc, but with the per_cpu() allocation. I'll test this theory out by
> not even allocating the pid masks and touching the per cpu data at every
> event to see if it crashes.

As pointed out in my other email, per-cpu allocation uses vmalloc when
size > PAGE_SIZE.

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com