ftrace: Move RCU is watching check after recursion check
commit b40341fa upstream. The first thing that the ftrace function callback helper functions should do is to check for recursion. Peter Zijlstra found that when "rcu_is_watching()" had its notrace removed, it caused perf function tracing to crash. This is because the call of rcu_is_watching() is tested before function recursion is checked and and if it is traced, it will cause an infinite recursion loop. rcu_is_watching() should still stay notrace, but to prevent this should never had crashed in the first place. The recursion prevention must be the first thing done in callback functions. Link: https://lore.kernel.org/r/20200929112541.GM2628@hirez.programming.kicks-ass.net Cc: stable@vger.kernel.org Cc: Paul McKenney <paulmck@kernel.org> Fixes: c68c0fa2 ("ftrace: Have ftrace_ops_get_func() handle RCU and PER_CPU flags too") Acked-by:Peter Zijlstra (Intel) <peterz@infradead.org> Reported-by:
Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by:
Steven Rostedt (VMware) <rostedt@goodmis.org> Signed-off-by:
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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d53cafaf
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