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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>
alistair/sunxi64-5.4-dsi
Steven Rostedt (VMware) 2019-08-30 16:30:01 -04:00
parent 7bd46644ea
commit 372e0d01da
1 changed files with 9 additions and 1 deletions
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10
kernel/trace/ftrace.c
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@ -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;