Fix: callstack context: false-sharing, bad memory size allocation

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/lttng-context-callstack.c b/lttng-context-callstack.c
index 6bfe794c2d58725b91a714516b77261ddd834385..3b7859eb8542b8c6bc073288f2380cf3b29e37fb 100644 (file)
--- a/lttng-context-callstack.c
+++ b/lttng-context-callstack.c
@@ -61,15 +61,20 @@
 #include "wrapper/vmalloc.h"
 #include "lttng-tracer.h"
 
-#define MAX_ENTRIES 25 /* BUG: saving more than 30 entries causes trace corruption */
+#define MAX_ENTRIES 25
+
+struct lttng_cs_nesting {
+       struct stack_trace stack_trace;
+       unsigned long entries[MAX_ENTRIES];
+};
 
 struct lttng_cs {
-       struct stack_trace items[RING_BUFFER_MAX_NESTING];
+       struct lttng_cs_nesting level[RING_BUFFER_MAX_NESTING];
 };
 
 struct field_data {
-       int mode;
        struct lttng_cs __percpu *cs_percpu;
+       int mode;
 };
 
 struct lttng_cs_type {
@@ -85,14 +90,14 @@ enum lttng_cs_ctx_modes {
 
 static struct lttng_cs_type cs_types[] = {
        {
-         .name           = "callstack_kernel",
-         .save_func_name = "save_stack_trace",
-         .save_func      = NULL,
+               .name           = "callstack_kernel",
+               .save_func_name = "save_stack_trace",
+               .save_func      = NULL,
        },
        {
-         .name           = "callstack_user",
-         .save_func_name = "save_stack_trace_user",
-         .save_func      = NULL,
+               .name           = "callstack_user",
+               .save_func_name = "save_stack_trace_user",
+               .save_func      = NULL,
        },
 };
 
@@ -133,7 +138,7 @@ struct stack_trace *stack_trace_context(struct lttng_ctx_field *field,
        if (nesting >= RING_BUFFER_MAX_NESTING) {
                return NULL;
        }
-       return &cs->items[nesting];
+       return &cs->level[nesting].stack_trace;
 }
 
 /*
@@ -180,8 +185,8 @@ size_t lttng_callstack_get_size(size_t offset, struct lttng_ctx_field *field,
 
 static
 void lttng_callstack_record(struct lttng_ctx_field *field,
-                           struct lib_ring_buffer_ctx *ctx,
-                           struct lttng_channel *chan)
+                       struct lib_ring_buffer_ctx *ctx,
+                       struct lttng_channel *chan)
 {
        struct stack_trace *trace = stack_trace_context(field, ctx);
        unsigned int nr_seq_entries;
@@ -207,31 +212,20 @@ void lttng_callstack_record(struct lttng_ctx_field *field,
 static
 void field_data_free(struct field_data *fdata)
 {
-       int cpu, i;
-       struct lttng_cs *cs;
-
        if (!fdata)
                return;
-       for_each_possible_cpu(cpu) {
-               cs = per_cpu_ptr(fdata->cs_percpu, cpu);
-               for (i = 0; i < RING_BUFFER_MAX_NESTING; i++) {
-                       kfree(cs->items[i].entries);
-               }
-       }
        free_percpu(fdata->cs_percpu);
        kfree(fdata);
 }
 
 static
-struct field_data __percpu *field_data_create(unsigned int entries, int type)
+struct field_data __percpu *field_data_create(int type)
 {
        int cpu, i;
-       struct stack_trace *item;
-       struct lttng_cs *cs;
        struct lttng_cs __percpu *cs_set;
-       struct field_data* fdata;
+       struct field_data *fdata;
 
-       fdata = kzalloc(sizeof(unsigned long) * entries, GFP_KERNEL);
+       fdata = kzalloc(sizeof(*fdata), GFP_KERNEL);
        if (!fdata)
                return NULL;
        cs_set = alloc_percpu(struct lttng_cs);
@@ -240,14 +234,15 @@ struct field_data __percpu *field_data_create(unsigned int entries, int type)
 
        fdata->cs_percpu = cs_set;
        for_each_possible_cpu(cpu) {
+               struct lttng_cs *cs;
+
                cs = per_cpu_ptr(cs_set, cpu);
                for (i = 0; i < RING_BUFFER_MAX_NESTING; i++) {
-                       item = &cs->items[i];
-                       item->entries = kzalloc(sizeof(unsigned long) * entries, GFP_KERNEL);
-                       if (!item->entries) {
-                               goto error_alloc;
-                       }
-                       item->max_entries = entries;
+                       struct lttng_cs_nesting *level;
+
+                       level = &cs->level[i];
+                       level->stack_trace.entries = level->entries;
+                       level->stack_trace.max_entries = MAX_ENTRIES;
                }
        }
        fdata->mode = type;
@@ -284,7 +279,7 @@ int __lttng_add_callstack_generic(struct lttng_ctx **ctx, int mode)
                ret = -EEXIST;
                goto error_find;
        }
-       fdata = field_data_create(MAX_ENTRIES, mode);
+       fdata = field_data_create(mode);
        if (!fdata) {
                ret = -ENOMEM;
                goto error_create;