Prevent re-entrancy in callstack-user context

[lttng-modules.git] / lttng-context-callstack.c

diff --git a/lttng-context-callstack.c b/lttng-context-callstack.c
index fd730bbc164090bdaf9ef708a4265894de2154a7..2fa5f52dbf19929ff2686a1e594dc5d22cbd724a 100644 (file)
--- a/lttng-context-callstack.c
+++ b/lttng-context-callstack.c
@@ -120,14 +120,26 @@ int init_type(enum lttng_cs_ctx_modes mode)
        return 0;
 }
 
+/* Keep track of nesting inside userspace callstack context code */
+DEFINE_PER_CPU(int, callstack_user_nesting);
+
 static
 struct stack_trace *stack_trace_context(struct lttng_ctx_field *field,
                                        struct lib_ring_buffer_ctx *ctx)
 {
-       int nesting;
+       int buffer_nesting, cs_user_nesting;
        struct lttng_cs *cs;
        struct field_data *fdata = field->priv;
 
+       /*
+        * Do not gather the userspace callstack context when the event was
+        * triggered by the userspace callstack context saving mechanism.
+        */
+       cs_user_nesting = per_cpu(callstack_user_nesting, ctx->cpu);
+
+       if (fdata->mode == CALLSTACK_USER && cs_user_nesting >= 1)
+               return NULL;
+
        /*
         * get_cpu() is not required, preemption is already
         * disabled while event is written.
@@ -136,11 +148,11 @@ struct stack_trace *stack_trace_context(struct lttng_ctx_field *field,
         * Check it again as a safety net.
         */
        cs = per_cpu_ptr(fdata->cs_percpu, ctx->cpu);
-       nesting = per_cpu(lib_ring_buffer_nesting, ctx->cpu) - 1;
-       if (nesting >= RING_BUFFER_MAX_NESTING) {
+       buffer_nesting = per_cpu(lib_ring_buffer_nesting, ctx->cpu) - 1;
+       if (buffer_nesting >= RING_BUFFER_MAX_NESTING)
                return NULL;
-       }
-       return &cs->dispatch[nesting].stack_trace;
+
+       return &cs->dispatch[buffer_nesting].stack_trace;
 }
 
 /*
@@ -168,8 +180,15 @@ size_t lttng_callstack_get_size(size_t offset, struct lttng_ctx_field *field,
        /* reset stack trace, no need to clear memory */
        trace->nr_entries = 0;
 
+       if (fdata->mode == CALLSTACK_USER)
+               ++per_cpu(callstack_user_nesting, ctx->cpu);
+
        /* do the real work and reserve space */
        cs_types[fdata->mode].save_func(trace);
+
+       if (fdata->mode == CALLSTACK_USER)
+               per_cpu(callstack_user_nesting, ctx->cpu)--;
+
        /*
         * Remove final ULONG_MAX delimiter. If we cannot find it, add
         * our own marker to show that the stack is incomplete. This is