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Commit 8ea63952 authored by Steven Rostedt (VMware)'s avatar Steven Rostedt (VMware) Committed by Greg Kroah-Hartman
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ftrace: Check for empty hash and comment the race with registering probes 



commit 372e0d01da71c84dcecf7028598a33813b0d5256 upstream.

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: 7b60f3d8 ("ftrace: Dynamically create the probe ftrace_ops for the trace_array")
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 9d98e0f4

kernel/trace/ftrace.c

+9 −1
Original line number Diff line number Diff line
@@ -3113,7 +3113,11 @@ 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;
@@ -4311,6 +4315,10 @@ 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;