ftrace: Rewrite of function graph tracer
Up until now, the function graph tracer could only have a single user
attached to it. If another user tried to attach to the function graph
tracer while one was already attached, it would fail. Allowing function
graph tracer to have more than one user has been asked for since 2009, but
it required a rewrite to the logic to pull it off so it never happened.
Until now!
There's three systems that trace the return of a function. That is
kretprobes, function graph tracer, and BPF. kretprobes and function graph
tracing both do it similarly. The difference is that kretprobes uses a
shadow stack per callback and function graph tracer creates a shadow stack
for all tasks. The function graph tracer method makes it possible to trace
the return of all functions. As kretprobes now needs that feature too,
allowing it to use function graph tracer was needed. BPF also wants to
trace the return of many probes and its method doesn't scale either.
Having it use function graph tracer would improve that.
By allowing function graph tracer to have multiple users allows both
kretprobes and BPF to use function graph tracer in these cases. This will
allow kretprobes code to be removed in the future as it's version will no
longer be needed. Note, function graph tracer is only limited to 16
simultaneous users, due to shadow stack size and allocated slots.
fgraph: Use str_plural() in test_graph_storage_single()
Use existing str_plural() function rather than duplicating its
implementation.
./kernel/trace/trace_selftest.c:880:56-60: opportunity for str_plural(size).
Link: https://lore.kernel.org/linux-trace-kernel/20240618072014.20855-1-jiapeng.chong@linux.alibaba.com
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Closes: https://bugzilla.openanolis.cn/show_bug.cgi?id=9349
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
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