ftrace: Check for empty hash and comment the race with registering probes
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: 7b60f3d876
("ftrace: Dynamically create the probe ftrace_ops for the trace_array")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
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@ -3096,7 +3096,11 @@ t_probe_next(struct seq_file *m, loff_t *pos)
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hash = iter->probe->ops.func_hash->filter_hash;
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if (!hash)
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/*
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* A probe being registered may temporarily have an empty hash
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* and it's at the end of the func_probes list.
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*/
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if (!hash || hash == EMPTY_HASH)
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return NULL;
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size = 1 << hash->size_bits;
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@ -4324,6 +4328,10 @@ register_ftrace_function_probe(char *glob, struct trace_array *tr,
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mutex_unlock(&ftrace_lock);
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/*
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* Note, there's a small window here that the func_hash->filter_hash
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* may be NULL or empty. Need to be carefule when reading the loop.
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*/
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mutex_lock(&probe->ops.func_hash->regex_lock);
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orig_hash = &probe->ops.func_hash->filter_hash;
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