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[Bug runtime/21859] on rawhide, the context.exp test case causes a kernel warning


https://sourceware.org/bugzilla/show_bug.cgi?id=21859

--- Comment #1 from David Smith <dsmith at redhat dot com> ---
The following kernel commit changed module_kallsyms_on_each_symbol(), which is
called by kallsyms_on_each_symbol, to quit doing RCU-style module list
traversal and require the module_mutex:

====
commit 0be964be0d45084245673c971d72a4b51690231d
Author: Peter Zijlstra <peterz@infradead.org>
Date:   Wed May 27 11:09:35 2015 +0930

    module: Sanitize RCU usage and locking

    Currently the RCU usage in module is an inconsistent mess of RCU and
    RCU-sched, this is broken for CONFIG_PREEMPT where synchronize_rcu()
    does not imply synchronize_sched().

    Most usage sites use preempt_{dis,en}able() which is RCU-sched, but
    (most of) the modification sites use synchronize_rcu(). With the
    exception of the module bug list, which actually uses RCU.

    Convert everything over to RCU-sched.

    Furthermore add lockdep asserts to all sites, because it's not at all
    clear to me the required locking is observed, esp. on exported
    functions.
====

It looks like this patch was first included in kernel version 4.2. So, we'll
have to hold the module_mutex when calling kallsyms_on_each_symbol().

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