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Date:   Thu, 30 Apr 2020 12:16:27 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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>
Subject: Re: [RFC][PATCH] x86/mm: Sync all vmalloc mappings before
 text_poke()
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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.

-- Steve