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
Unified · Split
| @@ -4421,10 +4421,9 @@ static void __init set_ftrace_early_graph(char *buf, int enable) · 4420 unmodified lines | ||
| 4421 | 4421 | char *func; |
| 4422 | 4422 | struct ftrace_hash *hash; |
| 4423 | 4423 | |
| 4424 | − if (enable) | |
| 4425 | − hash = ftrace_graph_hash; | |
| 4426 | − else | |
| 4427 | − hash = ftrace_graph_notrace_hash; | |
| 4424 | + hash = alloc_ftrace_hash(FTRACE_HASH_DEFAULT_BITS); | |
| 4425 | + if (WARN_ON(!hash)) | |
| 4426 | + return; | |
| 4428 | 4427 | |
| 4429 | 4428 | while (buf) { |
| 4430 | 4429 | func = strsep(&buf, ","); |
| @@ -4434,6 +4433,11 @@ static void __init set_ftrace_early_graph(char *buf, int enable) · 3 unmodified lines | ||
| 4434 | 4433 | printk(KERN_DEBUG "ftrace: function %s not " |
| 4435 | 4434 | "traceable\n", func); |
| 4436 | 4435 | } |
| 4436 | + | |
| 4437 | + if (enable) | |
| 4438 | + ftrace_graph_hash = hash; | |
| 4439 | + else | |
| 4440 | + ftrace_graph_notrace_hash = hash; | |
| 4437 | 4441 | } |
| 4438 | 4442 | #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ |
| 4439 | 4443 | |