ftrace: Check for empty hash and comment the race with registering probes (372e0d01) · Commits · 戴 / test

The race between adding a function probe and reading the probes that exist is very subtle. It needs a comment. Also, the issue can also happen if the probe has has the EMPTY_HASH as its func_hash. Cc: stable@vger.kernel.org Fixes: ("ftrace: Dynamically create the probe ftrace_ops for the trace_array") Signed-off-by:

Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/ftrace.c

+9 −1

Original line number	Diff line number	Diff line
		@@ -3096,7 +3096,11 @@ t_probe_next(struct seq_file m, loff_t pos)

		hash = iter->probe->ops.func_hash->filter_hash;

		if (!hash)
		/*
		* A probe being registered may temporarily have an empty hash
		* and it's at the end of the func_probes list.
		*/
		if (!hash \|\| hash == EMPTY_HASH)
		return NULL;

		size = 1 << hash->size_bits;
		@@ -4324,6 +4328,10 @@ register_ftrace_function_probe(char glob, struct trace_array tr,

		mutex_unlock(&ftrace_lock);

		/*
		* Note, there's a small window here that the func_hash->filter_hash
		* may be NULL or empty. Need to be carefule when reading the loop.
		*/
		mutex_lock(&probe->ops.func_hash->regex_lock);

		orig_hash = &probe->ops.func_hash->filter_hash;

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