function_graph: Add READ_ONCE() when accessing fgraph_array[]
In function_graph_enter() there's a loop that looks at fgraph_array[] elements which are fgraph_ops. It first tests if it is a fgraph_stub op, and if so skips it, as that's just there as a place holder. Then it checks the fgraph_ops filters to see if the ops wants to trace the current function. But if the compiler reloads the fgraph_array[] after the check against fgraph_stub, it could race with the fgraph_array[] being updated with the fgraph_stub. That would cause the stub to be processed. But the stub has a null "func_hash" field which will cause a NULL pointer dereference. Add a READ_ONCE() so that the gops that is compared against the fgraph_stub is also the gops that is processed later. Link: https://lore.kernel.org/all/CA+G9fYsSVJQZH=nM=1cjTc94PgSnMF9y65BnOv6XSoCG_b6wmw@mail.gmail.com/ Link: https://lore.kernel.org/linux-trace-kernel/20240613095223.1f07e3a4@rorschach.local.home Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Fixes: cc60ee813b503 ("function_graph: Use static_call and branch to optimize entry function") Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org> Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
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@ -641,7 +641,7 @@ int function_graph_enter(unsigned long ret, unsigned long func,
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{
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for_each_set_bit(i, &fgraph_array_bitmask,
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sizeof(fgraph_array_bitmask) * BITS_PER_BYTE) {
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struct fgraph_ops *gops = fgraph_array[i];
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struct fgraph_ops *gops = READ_ONCE(fgraph_array[i]);
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int save_curr_ret_stack;
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if (gops == &fgraph_stub)
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