diff options
| -rw-r--r-- | arch/sh/Kconfig | 1 | ||||
| -rw-r--r-- | arch/sh/kernel/ftrace.c | 146 |
2 files changed, 146 insertions, 1 deletions
diff --git a/arch/sh/Kconfig b/arch/sh/Kconfig index b940424f8ccc..5260fb55ab7f 100644 --- a/arch/sh/Kconfig +++ b/arch/sh/Kconfig @@ -38,6 +38,7 @@ config SUPERH32 select HAVE_DYNAMIC_FTRACE select HAVE_FUNCTION_TRACE_MCOUNT_TEST select HAVE_FTRACE_SYSCALLS + select HAVE_FTRACE_NMI_ENTER if DYNAMIC_FTRACE select HAVE_FUNCTION_GRAPH_TRACER select HAVE_ARCH_KGDB select ARCH_HIBERNATION_POSSIBLE if MMU diff --git a/arch/sh/kernel/ftrace.c b/arch/sh/kernel/ftrace.c index 2c48e267256e..b6f41c109beb 100644 --- a/arch/sh/kernel/ftrace.c +++ b/arch/sh/kernel/ftrace.c @@ -62,6 +62,150 @@ static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr) return ftrace_replaced_code; } +/* + * Modifying code must take extra care. On an SMP machine, if + * the code being modified is also being executed on another CPU + * that CPU will have undefined results and possibly take a GPF. + * We use kstop_machine to stop other CPUS from exectuing code. + * But this does not stop NMIs from happening. We still need + * to protect against that. We separate out the modification of + * the code to take care of this. + * + * Two buffers are added: An IP buffer and a "code" buffer. + * + * 1) Put the instruction pointer into the IP buffer + * and the new code into the "code" buffer. + * 2) Wait for any running NMIs to finish and set a flag that says + * we are modifying code, it is done in an atomic operation. + * 3) Write the code + * 4) clear the flag. + * 5) Wait for any running NMIs to finish. + * + * If an NMI is executed, the first thing it does is to call + * "ftrace_nmi_enter". This will check if the flag is set to write + * and if it is, it will write what is in the IP and "code" buffers. + * + * The trick is, it does not matter if everyone is writing the same + * content to the code location. Also, if a CPU is executing code + * it is OK to write to that code location if the contents being written + * are the same as what exists. + */ +#define MOD_CODE_WRITE_FLAG (1 << 31) /* set when NMI should do the write */ +static atomic_t nmi_running = ATOMIC_INIT(0); +static int mod_code_status; /* holds return value of text write */ +static void *mod_code_ip; /* holds the IP to write to */ +static void *mod_code_newcode; /* holds the text to write to the IP */ + +static unsigned nmi_wait_count; +static atomic_t nmi_update_count = ATOMIC_INIT(0); + +int ftrace_arch_read_dyn_info(char *buf, int size) +{ + int r; + + r = snprintf(buf, size, "%u %u", + nmi_wait_count, + atomic_read(&nmi_update_count)); + return r; +} + +static void clear_mod_flag(void) +{ + int old = atomic_read(&nmi_running); + + for (;;) { + int new = old & ~MOD_CODE_WRITE_FLAG; + + if (old == new) + break; + + old = atomic_cmpxchg(&nmi_running, old, new); + } +} + +static void ftrace_mod_code(void) +{ + /* + * Yes, more than one CPU process can be writing to mod_code_status. + * (and the code itself) + * But if one were to fail, then they all should, and if one were + * to succeed, then they all should. + */ + mod_code_status = probe_kernel_write(mod_code_ip, mod_code_newcode, + MCOUNT_INSN_SIZE); + + /* if we fail, then kill any new writers */ + if (mod_code_status) + clear_mod_flag(); +} + +void ftrace_nmi_enter(void) +{ + if (atomic_inc_return(&nmi_running) & MOD_CODE_WRITE_FLAG) { + smp_rmb(); + ftrace_mod_code(); + atomic_inc(&nmi_update_count); + } + /* Must have previous changes seen before executions */ + smp_mb(); +} + +void ftrace_nmi_exit(void) +{ + /* Finish all executions before clearing nmi_running */ + smp_mb(); + atomic_dec(&nmi_running); +} + +static void wait_for_nmi_and_set_mod_flag(void) +{ + if (!atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG)) + return; + + do { + cpu_relax(); + } while (atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG)); + + nmi_wait_count++; +} + +static void wait_for_nmi(void) +{ + if (!atomic_read(&nmi_running)) + return; + + do { + cpu_relax(); + } while (atomic_read(&nmi_running)); + + nmi_wait_count++; +} + +static int +do_ftrace_mod_code(unsigned long ip, void *new_code) +{ + mod_code_ip = (void *)ip; + mod_code_newcode = new_code; + + /* The buffers need to be visible before we let NMIs write them */ + smp_mb(); + + wait_for_nmi_and_set_mod_flag(); + + /* Make sure all running NMIs have finished before we write the code */ + smp_mb(); + + ftrace_mod_code(); + + /* Make sure the write happens before clearing the bit */ + smp_mb(); + + clear_mod_flag(); + wait_for_nmi(); + + return mod_code_status; +} + static int ftrace_modify_code(unsigned long ip, unsigned char *old_code, unsigned char *new_code) { @@ -86,7 +230,7 @@ static int ftrace_modify_code(unsigned long ip, unsigned char *old_code, return -EINVAL; /* replace the text with the new text */ - if (probe_kernel_write((void *)ip, new_code, MCOUNT_INSN_SIZE)) + if (do_ftrace_mod_code(ip, new_code)) return -EPERM; flush_icache_range(ip, ip + MCOUNT_INSN_SIZE); |