Use rseq for reserve position

[deliverable/lttng-ust.git] / libringbuffer / ring_buffer_frontend.c

diff --git a/libringbuffer/ring_buffer_frontend.c b/libringbuffer/ring_buffer_frontend.c
index 46751a2d8f58269a940c6efd3fa42f9a64a335c4..cda91dabcc8588d9c3f6b154357044b1ab37c236 100644 (file)
--- a/libringbuffer/ring_buffer_frontend.c
+++ b/libringbuffer/ring_buffer_frontend.c
@@ -74,6 +74,7 @@
 #include "shm.h"
 #include "tlsfixup.h"
 #include "../liblttng-ust/compat.h"    /* For ENODATA */
+#include "rseq.h"
 
 /* Print DBG() messages about events lost only every 1048576 hits */
 #define DBG_PRINT_NR_LOST      (1UL << 20)
@@ -2193,6 +2194,16 @@ int lib_ring_buffer_reserve_slow(struct lttng_ust_lib_ring_buffer_ctx *ctx)
        struct lttng_ust_lib_ring_buffer *buf;
        struct switch_offsets offsets;
        int ret;
+       struct lttng_rseq_state rseq_state;
+
+       if (caa_likely(ctx->ctx_len
+                       >= sizeof(struct lttng_ust_lib_ring_buffer_ctx))) {
+               rseq_state = ctx->rseq_state;
+       } else {
+               rseq_state.cpu_id = -2;
+               rseq_state.event_counter = 0;
+               rseq_state.rseqp = NULL;
+       }
 
        if (config->alloc == RING_BUFFER_ALLOC_PER_CPU)
                buf = shmp(handle, chan->backend.buf[ctx->cpu].shmp);
@@ -2204,14 +2215,30 @@ int lib_ring_buffer_reserve_slow(struct lttng_ust_lib_ring_buffer_ctx *ctx)
 
        offsets.size = 0;
 
-       do {
-               ret = lib_ring_buffer_try_reserve_slow(buf, chan, &offsets,
-                                                      ctx);
+       if (caa_unlikely(config->sync == RING_BUFFER_SYNC_GLOBAL
+                       || rseq_state.cpu_id < 0
+                       || uatomic_read(&chan->u.reserve_fallback_ref))) {
+               do {
+                       ret = lib_ring_buffer_try_reserve_slow(buf, chan,
+                                       &offsets, ctx);
+                       if (caa_unlikely(ret))
+                               return ret;
+               } while (caa_unlikely(v_cmpxchg(config, &buf->offset,
+                                       offsets.old, offsets.end)
+                               != offsets.old));
+       } else {
+               ret = lib_ring_buffer_try_reserve_slow(buf, chan,
+                               &offsets, ctx);
                if (caa_unlikely(ret))
                        return ret;
-       } while (caa_unlikely(v_cmpxchg(config, &buf->offset, offsets.old,
-                                   offsets.end)
-                         != offsets.old));
+               if (caa_unlikely(buf->offset.a != offsets.old))
+                       return -EAGAIN;
+               if (caa_unlikely(!__rseq_finish(NULL, 0, NULL, NULL, 0,
+                               (intptr_t *) &buf->offset.a,
+                               (intptr_t) offsets.end,
+                               rseq_state, RSEQ_FINISH_SINGLE, false)))
+                       return -EAGAIN;
+       }
 
        /*
         * Atomically update last_tsc. This update races against concurrent