The function kgdb_breakpoint() sets up break point at compile time by calling arch_kgdb_breakpoint(); Though this call is surrounded by wmb() barrier, the compile can still re-order the break point, because this scheduling barrier is not a code motion barrier in gcc. Making kgdb_breakpoint() as noinline solves this problem of code reording around break point instruction and also avoids problem of being called as inline function from other places More details about discussion on this can be found here http://comments.gmane.org/gmane.linux.ports.arm.kernel/269732
Unified · Split
| @@ -1035,7 +1035,7 @@ int dbg_io_get_char(void) · 1034 unmodified lines | ||
| 1035 | 1035 | * otherwise as a quick means to stop program execution and "break" into |
| 1036 | 1036 | * the debugger. |
| 1037 | 1037 | */ |
| 1038 | −void kgdb_breakpoint(void) | |
| 1038 | +noinline void kgdb_breakpoint(void) | |
| 1039 | 1039 | { |
| 1040 | 1040 | atomic_inc(&kgdb_setting_breakpoint); |
| 1041 | 1041 | wmb(); /* Sync point before breakpoint */ |