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ftrace: Move RCU is watching check after recursion check

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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: c68c0fa293 ("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>
This commit is contained in:
Steven Rostedt (VMware) 2020-09-29 12:40:31 -04:00
parent 851e6f61cd
commit b40341fad6
1 changed files with 2 additions and 4 deletions
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6
kernel/trace/ftrace.c
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@ -6993,16 +6993,14 @@ static void ftrace_ops_assist_func(unsigned long ip, unsigned long parent_ip,
{
int bit;
if ((op->flags & FTRACE_OPS_FL_RCU) && !rcu_is_watching())
return;
bit = trace_test_and_set_recursion(TRACE_LIST_START, TRACE_LIST_MAX);
if (bit < 0)
return;
preempt_disable_notrace();
op->func(ip, parent_ip, op, regs);
if (!(op->flags & FTRACE_OPS_FL_RCU) || rcu_is_watching())
op->func(ip, parent_ip, op, regs);
preempt_enable_notrace();
trace_clear_recursion(bit);