From 54a58b2856377e18ea6a42706bea0304a8d7845e Mon Sep 17 00:00:00 2001 From: Thomas Hellstrom Date: Tue, 19 Sep 2017 19:41:22 +0200 Subject: [PATCH] loader/dri3: Improve dri3 thread-safety MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit It turned out that with recent changes that call into dri3 from glFinish(), it appears like different thread end up waiting for X events simultaneously, causing deadlocks since they steal events from eachoter and update the dri3 counters behind eachothers backs. This patch intends to improve on that. It allows at most one thread at a time to wait on events for a single drawable. If another thread intends to do the same, it's put to sleep until the first thread finishes waiting, and then it rechecks counters and optionally retries the waiting. Threads that poll for X events never pulls X events off the event queue if there are other threads waiting for events on that drawable. Counters in the dri3 drawable structure are protected by a mutex. Finally, the mutex we introduce is never held while waiting for the X server to avoid unnecessary stalls. This does not make dri3 drawables completely thread-safe but at least it's a first step. Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=102358 Fixes: d5ba75f8881 "st/dri2 Plumb the flush_swapbuffer functionality through to dri3" Signed-off-by: Thomas Hellstrom Acked-by: Nicolai Hähnle --- src/loader/loader_dri3_helper.c | 77 +++++++++++++++++++++++++-------- src/loader/loader_dri3_helper.h | 10 +++++ 2 files changed, 69 insertions(+), 18 deletions(-) diff --git a/src/loader/loader_dri3_helper.c b/src/loader/loader_dri3_helper.c index 19ab5815100..7e6b8b2e056 100644 --- a/src/loader/loader_dri3_helper.c +++ b/src/loader/loader_dri3_helper.c @@ -32,7 +32,6 @@ #include -#include #include "loader_dri3_helper.h" /* From xmlpool/options.h, user exposed so should be stable */ @@ -186,8 +185,11 @@ dri3_fence_await(xcb_connection_t *c, struct loader_dri3_drawable *draw, { xcb_flush(c); xshmfence_await(buffer->shm_fence); - if (draw) + if (draw) { + mtx_lock(&draw->mtx); dri3_flush_present_events(draw); + mtx_unlock(&draw->mtx); + } } static void @@ -245,6 +247,9 @@ loader_dri3_drawable_fini(struct loader_dri3_drawable *draw) xcb_discard_reply(draw->conn, cookie.sequence); xcb_unregister_for_special_event(draw->conn, draw->special_event); } + + cnd_destroy(&draw->event_cnd); + mtx_destroy(&draw->mtx); } int @@ -276,6 +281,8 @@ loader_dri3_drawable_init(xcb_connection_t *conn, draw->cur_blit_source = -1; draw->back_format = __DRI_IMAGE_FORMAT_NONE; + mtx_init(&draw->mtx, mtx_plain); + cnd_init(&draw->event_cnd); if (draw->ext->config) draw->ext->config->configQueryi(draw->dri_screen, @@ -407,13 +414,27 @@ dri3_handle_present_event(struct loader_dri3_drawable *draw, } static bool -dri3_wait_for_event(struct loader_dri3_drawable *draw) +dri3_wait_for_event_locked(struct loader_dri3_drawable *draw) { xcb_generic_event_t *ev; xcb_present_generic_event_t *ge; xcb_flush(draw->conn); - ev = xcb_wait_for_special_event(draw->conn, draw->special_event); + + /* Only have one thread waiting for events at a time */ + if (draw->has_event_waiter) { + cnd_wait(&draw->event_cnd, &draw->mtx); + /* Another thread has updated the protected info, so retest. */ + return true; + } else { + draw->has_event_waiter = true; + /* Allow other threads access to the drawable while we're waiting. */ + mtx_unlock(&draw->mtx); + ev = xcb_wait_for_special_event(draw->conn, draw->special_event); + mtx_lock(&draw->mtx); + draw->has_event_waiter = false; + cnd_broadcast(&draw->event_cnd); + } if (!ev) return false; ge = (void *) ev; @@ -442,19 +463,23 @@ loader_dri3_wait_for_msc(struct loader_dri3_drawable *draw, divisor, remainder); + mtx_lock(&draw->mtx); xcb_flush(draw->conn); /* Wait for the event */ if (draw->special_event) { while ((int32_t) (msc_serial - draw->recv_msc_serial) > 0) { - if (!dri3_wait_for_event(draw)) + if (!dri3_wait_for_event_locked(draw)) { + mtx_unlock(&draw->mtx); return false; + } } } *ust = draw->notify_ust; *msc = draw->notify_msc; *sbc = draw->recv_sbc; + mtx_unlock(&draw->mtx); return true; } @@ -476,17 +501,21 @@ loader_dri3_wait_for_sbc(struct loader_dri3_drawable *draw, * swaps requested with glXSwapBuffersMscOML for that window have * completed." */ + mtx_lock(&draw->mtx); if (!target_sbc) target_sbc = draw->send_sbc; while (draw->recv_sbc < target_sbc) { - if (!dri3_wait_for_event(draw)) + if (!dri3_wait_for_event_locked(draw)) { + mtx_unlock(&draw->mtx); return 0; + } } *ust = draw->ust; *msc = draw->msc; *sbc = draw->recv_sbc; + mtx_unlock(&draw->mtx); return 1; } @@ -499,16 +528,16 @@ static int dri3_find_back(struct loader_dri3_drawable *draw) { int b; - xcb_generic_event_t *ev; - xcb_present_generic_event_t *ge; - int num_to_consider = draw->num_back; + int num_to_consider; + mtx_lock(&draw->mtx); /* Increase the likelyhood of reusing current buffer */ dri3_flush_present_events(draw); /* Check whether we need to reuse the current back buffer as new back. * In that case, wait until it's not busy anymore. */ + num_to_consider = draw->num_back; if (!loader_dri3_have_image_blit(draw) && draw->cur_blit_source != -1) { num_to_consider = 1; draw->cur_blit_source = -1; @@ -521,15 +550,14 @@ dri3_find_back(struct loader_dri3_drawable *draw) if (!buffer || !buffer->busy) { draw->cur_back = id; + mtx_unlock(&draw->mtx); return id; } } - xcb_flush(draw->conn); - ev = xcb_wait_for_special_event(draw->conn, draw->special_event); - if (!ev) + if (!dri3_wait_for_event_locked(draw)) { + mtx_unlock(&draw->mtx); return -1; - ge = (void *) ev; - dri3_handle_present_event(draw, ge); + } } } @@ -745,6 +773,9 @@ dri3_flush_present_events(struct loader_dri3_drawable *draw) /* Check to see if any configuration changes have occurred * since we were last invoked */ + if (draw->has_event_waiter) + return; + if (draw->special_event) { xcb_generic_event_t *ev; @@ -774,6 +805,7 @@ loader_dri3_swap_buffers_msc(struct loader_dri3_drawable *draw, back = dri3_find_back_alloc(draw); + mtx_lock(&draw->mtx); if (draw->is_different_gpu && back) { /* Update the linear buffer before presenting the pixmap */ (void) loader_dri3_blit_image(draw, @@ -893,6 +925,7 @@ loader_dri3_swap_buffers_msc(struct loader_dri3_drawable *draw, if (draw->stamp) ++(*draw->stamp); } + mtx_unlock(&draw->mtx); draw->ext->flush->invalidate(draw->dri_drawable); @@ -903,11 +936,14 @@ int loader_dri3_query_buffer_age(struct loader_dri3_drawable *draw) { struct loader_dri3_buffer *back = dri3_find_back_alloc(draw); + int ret; - if (!back || back->last_swap == 0) - return 0; + mtx_lock(&draw->mtx); + ret = (!back || back->last_swap == 0) ? 0 : + draw->send_sbc - back->last_swap + 1; + mtx_unlock(&draw->mtx); - return draw->send_sbc - back->last_swap + 1; + return ret; } /** loader_dri3_open @@ -1125,6 +1161,7 @@ static int dri3_update_drawable(__DRIdrawable *driDrawable, struct loader_dri3_drawable *draw) { + mtx_lock(&draw->mtx); if (draw->first_init) { xcb_get_geometry_cookie_t geom_cookie; xcb_get_geometry_reply_t *geom_reply; @@ -1165,8 +1202,10 @@ dri3_update_drawable(__DRIdrawable *driDrawable, geom_reply = xcb_get_geometry_reply(draw->conn, geom_cookie, NULL); - if (!geom_reply) + if (!geom_reply) { + mtx_unlock(&draw->mtx); return false; + } draw->width = geom_reply->width; draw->height = geom_reply->height; @@ -1198,6 +1237,7 @@ dri3_update_drawable(__DRIdrawable *driDrawable, if (error) { if (error->error_code != BadWindow) { free(error); + mtx_unlock(&draw->mtx); return false; } draw->is_pixmap = true; @@ -1206,6 +1246,7 @@ dri3_update_drawable(__DRIdrawable *driDrawable, } } dri3_flush_present_events(draw); + mtx_unlock(&draw->mtx); return true; } diff --git a/src/loader/loader_dri3_helper.h b/src/loader/loader_dri3_helper.h index d3f4b0c00a9..0dd37e91717 100644 --- a/src/loader/loader_dri3_helper.h +++ b/src/loader/loader_dri3_helper.h @@ -33,6 +33,7 @@ #include #include +#include enum loader_dri3_buffer_type { loader_dri3_buffer_back = 0, @@ -159,6 +160,15 @@ struct loader_dri3_drawable { unsigned int swap_method; unsigned int back_format; + + /* Currently protects the following fields: + * event_cnd, has_event_waiter, + * recv_sbc, ust, msc, recv_msc_serial, + * notify_ust, notify_msc + */ + mtx_t mtx; + cnd_t event_cnd; + bool has_event_waiter; }; void -- 2.30.2