Re: [RFC][PATCH] x86/mm: Sync all vmalloc mappings before text_poke()

Steven Rostedt
2020-04-30T16:16:32Z

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