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

Mathieu Desnoyers
2020-04-30T16:18:29Z

----- 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.