Commit 92ad18ec authored Mar 02, 2017 by Steven Rostedt (VMware)

ftrace/graph: Do not modify the EMPTY_HASH for the function_graph filter

On boot up, if the kernel command line sets a graph funtion with the kernel
command line options "ftrace_graph_filter" or "ftrace_graph_notrace" then it
updates the corresponding function graph hash, ftrace_graph_hash or
ftrace_graph_notrace_hash respectively. Unfortunately, at boot up, these
variables are pointers to the "EMPTY_HASH" which is a constant used as a
placeholder when a hash has no entities. The problem was that the comand
line version to set the hashes updated the actual EMPTY_HASH instead of
creating a new hash for the function graph. This broke the EMPTY_HASH
because not only did it modify a constant (not sure how that was allowed to
happen, except maybe because it was done at early boot, const variables were
still mutable), but it made the filters have functions listed in them when
they were actually empty.

The kernel command line function needs to allocate a new hash for the
function graph filters and assign the necessary variables to that new hash
instead.

Link: http://lkml.kernel.org/r/1488420091.7212.17.camel@linux.intel.com

Cc: Namhyung Kim <namhyung@kernel.org>
Fixes: b9b0c831 ("ftrace: Convert graph filter to use hash tables")
Reported-by: Todd Brandt <todd.e.brandt@linux.intel.com>
Tested-by: Todd Brandt <todd.e.brandt@linux.intel.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

parent 3a150df9

kernel/trace/ftrace.c

+8 −4

Original line number	Diff line number	Diff line
		@@ -4421,10 +4421,9 @@ static void __init set_ftrace_early_graph(char *buf, int enable)
		char *func;
		struct ftrace_hash *hash;

		if (enable)
		hash = ftrace_graph_hash;
		else
		hash = ftrace_graph_notrace_hash;
		hash = alloc_ftrace_hash(FTRACE_HASH_DEFAULT_BITS);
		if (WARN_ON(!hash))
		return;

		while (buf) {
		func = strsep(&buf, ",");
		@@ -4434,6 +4433,11 @@ static void __init set_ftrace_early_graph(char *buf, int enable)
		printk(KERN_DEBUG "ftrace: function %s not "
		"traceable\n", func);
		}

		if (enable)
		ftrace_graph_hash = hash;
		else
		ftrace_graph_notrace_hash = hash;
		}
		#endif /* CONFIG_FUNCTION_GRAPH_TRACER */

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