From: Pratyush Anand <panand@xxxxxxxxxx> 3.4.108-rc1 review patch. If anyone has any objections, please let me know. ------------------ commit 1619dc3f8f555ee1cdd3c75db3885d5715442b12 upstream. When ftrace is enabled globally through the proc interface, we must check if ftrace_graph_active is set. If it is set, then we should also pass the FTRACE_START_FUNC_RET command to ftrace_run_update_code(). Similarly, when ftrace is disabled globally through the proc interface, we must check if ftrace_graph_active is set. If it is set, then we should also pass the FTRACE_STOP_FUNC_RET command to ftrace_run_update_code(). Consider the following situation. # echo 0 > /proc/sys/kernel/ftrace_enabled After this ftrace_enabled = 0. # echo function_graph > /sys/kernel/debug/tracing/current_tracer Since ftrace_enabled = 0, ftrace_enable_ftrace_graph_caller() is never called. # echo 1 > /proc/sys/kernel/ftrace_enabled Now ftrace_enabled will be set to true, but still ftrace_enable_ftrace_graph_caller() will not be called, which is not desired. Further if we execute the following after this: # echo nop > /sys/kernel/debug/tracing/current_tracer Now since ftrace_enabled is set it will call ftrace_disable_ftrace_graph_caller(), which causes a kernel warning on the ARM platform. On the ARM platform, when ftrace_enable_ftrace_graph_caller() is called, it checks whether the old instruction is a nop or not. If it's not a nop, then it returns an error. If it is a nop then it replaces instruction at that address with a branch to ftrace_graph_caller. ftrace_disable_ftrace_graph_caller() behaves just the opposite. Therefore, if generic ftrace code ever calls either ftrace_enable_ftrace_graph_caller() or ftrace_disable_ftrace_graph_caller() consecutively two times in a row, then it will return an error, which will cause the generic ftrace code to raise a warning. Note, x86 does not have an issue with this because the architecture specific code for ftrace_enable_ftrace_graph_caller() and ftrace_disable_ftrace_graph_caller() does not check the previous state, and calling either of these functions twice in a row has no ill effect. Link: http://lkml.kernel.org/r/e4fbe64cdac0dd0e86a3bf914b0f83c0b419f146.1425666454.git.panand@xxxxxxxxxx Signed-off-by: Pratyush Anand <panand@xxxxxxxxxx> [ removed extra if (ftrace_start_up) and defined ftrace_graph_active as 0 if CONFIG_FUNCTION_GRAPH_TRACER is not set. ] Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx> [lizf: Backported to 3.4: adjust context] Signed-off-by: Zefan Li <lizefan@xxxxxxxxxx> --- kernel/trace/ftrace.c | 27 ++++++++++++++++++++++----- 1 file changed, 22 insertions(+), 5 deletions(-) diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index 5b6bd45..d73d0b7 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -1014,6 +1014,12 @@ ftrace_filter_lseek(struct file *file, loff_t offset, int whence) return ret; } +#ifdef CONFIG_FUNCTION_GRAPH_TRACER +static int ftrace_graph_active; +#else +# define ftrace_graph_active 0 +#endif + #ifdef CONFIG_DYNAMIC_FTRACE #ifndef CONFIG_FTRACE_MCOUNT_RECORD @@ -2056,24 +2062,36 @@ static int ftrace_shutdown(struct ftrace_ops *ops, int command) static void ftrace_startup_sysctl(void) { + int command; + if (unlikely(ftrace_disabled)) return; /* Force update next time */ saved_ftrace_func = NULL; /* ftrace_start_up is true if we want ftrace running */ - if (ftrace_start_up) - ftrace_run_update_code(FTRACE_UPDATE_CALLS); + if (ftrace_start_up) { + command = FTRACE_UPDATE_CALLS; + if (ftrace_graph_active) + command |= FTRACE_START_FUNC_RET; + ftrace_run_update_code(command); + } } static void ftrace_shutdown_sysctl(void) { + int command; + if (unlikely(ftrace_disabled)) return; /* ftrace_start_up is true if ftrace is running */ - if (ftrace_start_up) - ftrace_run_update_code(FTRACE_DISABLE_CALLS); + if (ftrace_start_up) { + command = FTRACE_DISABLE_CALLS; + if (ftrace_graph_active) + command |= FTRACE_STOP_FUNC_RET; + ftrace_run_update_code(command); + } } static cycle_t ftrace_update_time; @@ -4465,7 +4483,6 @@ ftrace_enable_sysctl(struct ctl_table *table, int write, #ifdef CONFIG_FUNCTION_GRAPH_TRACER -static int ftrace_graph_active; static struct notifier_block ftrace_suspend_notifier; int ftrace_graph_entry_stub(struct ftrace_graph_ent *trace) -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html