tracing: Prevent buffer overwrite disabled for latency tracers

The latency tracers require the buffers to be in overwrite mode,
otherwise they get screwed up. Force the buffers to stay in overwrite
mode when latency tracers are enabled.

Added a flag_changed() method to the tracer structure to allow
the tracers to see what flags are being changed, and also be able
to prevent the change from happing.

Cc: stable@vger.kernel.org
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 02debabe9ed408eb011e2475cd22865e4e1a80b1..4f1dade56981d6fe5d880e9f6caaf609ab1e9c02 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2881,11 +2881,25 @@ static int set_tracer_option(struct tracer *trace, char *cmp, int neg)
        return -EINVAL;
 }
 
-static void set_tracer_flags(unsigned int mask, int enabled)
+/* Some tracers require overwrite to stay enabled */
+int trace_keep_overwrite(struct tracer *tracer, u32 mask, int set)
+{
+       if (tracer->enabled && (mask & TRACE_ITER_OVERWRITE) && !set)
+               return -1;
+
+       return 0;
+}
+
+int set_tracer_flag(unsigned int mask, int enabled)
 {
        /* do nothing if flag is already set */
        if (!!(trace_flags & mask) == !!enabled)
-               return;
+               return 0;
+
+       /* Give the tracer a chance to approve the change */
+       if (current_trace->flag_changed)
+               if (current_trace->flag_changed(current_trace, mask, !!enabled))
+                       return -EINVAL;
 
        if (enabled)
                trace_flags |= mask;
@@ -2904,13 +2918,15 @@ static void set_tracer_flags(unsigned int mask, int enabled)
 
        if (mask == TRACE_ITER_PRINTK)
                trace_printk_start_stop_comm(enabled);
+
+       return 0;
 }
 
 static int trace_set_options(char *option)
 {
        char *cmp;
        int neg = 0;
-       int ret = 0;
+       int ret = -ENODEV;
        int i;
 
        cmp = strstrip(option);
@@ -2924,7 +2940,7 @@ static int trace_set_options(char *option)
 
        for (i = 0; trace_options[i]; i++) {
                if (strcmp(cmp, trace_options[i]) == 0) {
-                       set_tracer_flags(1 << i, !neg);
+                       ret = set_tracer_flag(1 << i, !neg);
                        break;
                }
        }
@@ -2943,6 +2959,7 @@ tracing_trace_options_write(struct file *filp, const char __user *ubuf,
                        size_t cnt, loff_t *ppos)
 {
        char buf[64];
+       int ret;
 
        if (cnt >= sizeof(buf))
                return -EINVAL;
@@ -2952,7 +2969,9 @@ tracing_trace_options_write(struct file *filp, const char __user *ubuf,
 
        buf[cnt] = 0;
 
-       trace_set_options(buf);
+       ret = trace_set_options(buf);
+       if (ret < 0)
+               return ret;
 
        *ppos += cnt;
 
@@ -3256,6 +3275,9 @@ static int tracing_set_tracer(const char *buf)
                goto out;
 
        trace_branch_disable();
+
+       current_trace->enabled = false;
+
        if (current_trace->reset)
                current_trace->reset(tr);
 
@@ -3300,6 +3322,7 @@ static int tracing_set_tracer(const char *buf)
        }
 
        current_trace = t;
+       current_trace->enabled = true;
        trace_branch_enable(tr);
  out:
        mutex_unlock(&trace_types_lock);
@@ -4788,9 +4811,12 @@ trace_options_core_write(struct file *filp, const char __user *ubuf, size_t cnt,
                return -EINVAL;
 
        mutex_lock(&trace_types_lock);
-       set_tracer_flags(1 << index, val);
+       ret = set_tracer_flag(1 << index, val);
        mutex_unlock(&trace_types_lock);
 
+       if (ret < 0)
+               return ret;
+
        *ppos += cnt;
 
        return cnt;

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 57d7e5397d56da86f667e3139fb14703a99e8fcf..2081971367ea8e54d5b42e188c7aaaaee22c8f2a 100644 (file)
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -283,11 +283,15 @@ struct tracer {
        enum print_line_t       (*print_line)(struct trace_iterator *iter);
        /* If you handled the flag setting, return 0 */
        int                     (*set_flag)(u32 old_flags, u32 bit, int set);
+       /* Return 0 if OK with change, else return non-zero */
+       int                     (*flag_changed)(struct tracer *tracer,
+                                               u32 mask, int set);
        struct tracer           *next;
        struct tracer_flags     *flags;
        bool                    print_max;
        bool                    use_max_tr;
        bool                    allocated_snapshot;
+       bool                    enabled;
 };
 
 
@@ -943,6 +947,8 @@ extern const char *__stop___trace_bprintk_fmt[];
 
 void trace_printk_init_buffers(void);
 void trace_printk_start_comm(void);
+int trace_keep_overwrite(struct tracer *tracer, u32 mask, int set);
+int set_tracer_flag(unsigned int mask, int enabled);
 
 #undef FTRACE_ENTRY
 #define FTRACE_ENTRY(call, struct_name, id, tstruct, print, filter)    \

diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
index 713a2cac48816461c0c0a5b11d5a854ea5c4b3d3..443b25b43b4f60f3b58102daab06c6150f01ad64 100644 (file)
--- a/kernel/trace/trace_irqsoff.c
+++ b/kernel/trace/trace_irqsoff.c
@@ -32,7 +32,7 @@ enum {
 
 static int trace_type __read_mostly;
 
-static int save_lat_flag;
+static int save_flags;
 
 static void stop_irqsoff_tracer(struct trace_array *tr, int graph);
 static int start_irqsoff_tracer(struct trace_array *tr, int graph);
@@ -558,8 +558,11 @@ static void stop_irqsoff_tracer(struct trace_array *tr, int graph)
 
 static void __irqsoff_tracer_init(struct trace_array *tr)
 {
-       save_lat_flag = trace_flags & TRACE_ITER_LATENCY_FMT;
-       trace_flags |= TRACE_ITER_LATENCY_FMT;
+       save_flags = trace_flags;
+
+       /* non overwrite screws up the latency tracers */
+       set_tracer_flag(TRACE_ITER_OVERWRITE, 1);
+       set_tracer_flag(TRACE_ITER_LATENCY_FMT, 1);
 
        tracing_max_latency = 0;
        irqsoff_trace = tr;
@@ -573,10 +576,13 @@ static void __irqsoff_tracer_init(struct trace_array *tr)
 
 static void irqsoff_tracer_reset(struct trace_array *tr)
 {
+       int lat_flag = save_flags & TRACE_ITER_LATENCY_FMT;
+       int overwrite_flag = save_flags & TRACE_ITER_OVERWRITE;
+
        stop_irqsoff_tracer(tr, is_graph());
 
-       if (!save_lat_flag)
-               trace_flags &= ~TRACE_ITER_LATENCY_FMT;
+       set_tracer_flag(TRACE_ITER_LATENCY_FMT, lat_flag);
+       set_tracer_flag(TRACE_ITER_OVERWRITE, overwrite_flag);
 }
 
 static void irqsoff_tracer_start(struct trace_array *tr)
@@ -609,6 +615,7 @@ static struct tracer irqsoff_tracer __read_mostly =
        .print_line     = irqsoff_print_line,
        .flags          = &tracer_flags,
        .set_flag       = irqsoff_set_flag,
+       .flag_changed   = trace_keep_overwrite,
 #ifdef CONFIG_FTRACE_SELFTEST
        .selftest    = trace_selftest_startup_irqsoff,
 #endif
@@ -642,6 +649,7 @@ static struct tracer preemptoff_tracer __read_mostly =
        .print_line     = irqsoff_print_line,
        .flags          = &tracer_flags,
        .set_flag       = irqsoff_set_flag,
+       .flag_changed   = trace_keep_overwrite,
 #ifdef CONFIG_FTRACE_SELFTEST
        .selftest    = trace_selftest_startup_preemptoff,
 #endif
@@ -677,6 +685,7 @@ static struct tracer preemptirqsoff_tracer __read_mostly =
        .print_line     = irqsoff_print_line,
        .flags          = &tracer_flags,
        .set_flag       = irqsoff_set_flag,
+       .flag_changed   = trace_keep_overwrite,
 #ifdef CONFIG_FTRACE_SELFTEST
        .selftest    = trace_selftest_startup_preemptirqsoff,
 #endif

diff --git a/kernel/trace/trace_sched_wakeup.c b/kernel/trace/trace_sched_wakeup.c
index 75aa97fbe1a11120d93ed241e00ddbac5a51a55d..fde652c9a511c197d47822b66871ffb764f62539 100644 (file)
--- a/kernel/trace/trace_sched_wakeup.c
+++ b/kernel/trace/trace_sched_wakeup.c
@@ -36,7 +36,7 @@ static void __wakeup_reset(struct trace_array *tr);
 static int wakeup_graph_entry(struct ftrace_graph_ent *trace);
 static void wakeup_graph_return(struct ftrace_graph_ret *trace);
 
-static int save_lat_flag;
+static int save_flags;
 
 #define TRACE_DISPLAY_GRAPH     1
 
@@ -540,8 +540,11 @@ static void stop_wakeup_tracer(struct trace_array *tr)
 
 static int __wakeup_tracer_init(struct trace_array *tr)
 {
-       save_lat_flag = trace_flags & TRACE_ITER_LATENCY_FMT;
-       trace_flags |= TRACE_ITER_LATENCY_FMT;
+       save_flags = trace_flags;
+
+       /* non overwrite screws up the latency tracers */
+       set_tracer_flag(TRACE_ITER_OVERWRITE, 1);
+       set_tracer_flag(TRACE_ITER_LATENCY_FMT, 1);
 
        tracing_max_latency = 0;
        wakeup_trace = tr;
@@ -563,12 +566,15 @@ static int wakeup_rt_tracer_init(struct trace_array *tr)
 
 static void wakeup_tracer_reset(struct trace_array *tr)
 {
+       int lat_flag = save_flags & TRACE_ITER_LATENCY_FMT;
+       int overwrite_flag = save_flags & TRACE_ITER_OVERWRITE;
+
        stop_wakeup_tracer(tr);
        /* make sure we put back any tasks we are tracing */
        wakeup_reset(tr);
 
-       if (!save_lat_flag)
-               trace_flags &= ~TRACE_ITER_LATENCY_FMT;
+       set_tracer_flag(TRACE_ITER_LATENCY_FMT, lat_flag);
+       set_tracer_flag(TRACE_ITER_OVERWRITE, overwrite_flag);
 }
 
 static void wakeup_tracer_start(struct trace_array *tr)
@@ -594,6 +600,7 @@ static struct tracer wakeup_tracer __read_mostly =
        .print_line     = wakeup_print_line,
        .flags          = &tracer_flags,
        .set_flag       = wakeup_set_flag,
+       .flag_changed   = trace_keep_overwrite,
 #ifdef CONFIG_FTRACE_SELFTEST
        .selftest    = trace_selftest_startup_wakeup,
 #endif
@@ -615,6 +622,7 @@ static struct tracer wakeup_rt_tracer __read_mostly =
        .print_line     = wakeup_print_line,
        .flags          = &tracer_flags,
        .set_flag       = wakeup_set_flag,
+       .flag_changed   = trace_keep_overwrite,
 #ifdef CONFIG_FTRACE_SELFTEST
        .selftest    = trace_selftest_startup_wakeup,
 #endif