Commit 9df6cda3 authored by Aaron Plattner's avatar Aaron Plattner Committed by Rui Matos

compositor: Fix GL_EXT_x11_sync_object race condition

The compositor maintains a ring of shared fences with the X server in order to
properly synchronize rendering between the X server and the compositor's GPU
channel.  When all of the fences have been used, the compositor needs to reset
one so that it can be reused.  It does this by first waiting on the CPU for the
fence to become triggered, and then sending a request to the X server to reset
the fence.

If the compositor's GPU channel is busy processing other work (e.g. the desktop
switcher animation), then the X server may process the reset request before the
GPU has consumed the fence.  This causes the GPU channel to hang.

Fix the problem by having the compositor's GPU channel trigger its own fence
after waiting for the X server's fence.  Wait for that fence on the CPU before
sending the reset request to the X server.  This ensures that the GPU has
consumed the X11 fence before the server resets it.
Signed-off-by: default avatarAaron Plattner <aplattner@nvidia.com>

https://bugzilla.gnome.org/show_bug.cgi?id=728464
parent 39763d4a
......@@ -73,7 +73,8 @@ typedef struct
Display *xdisplay;
XSyncFence xfence;
GLsync glsync;
GLsync gl_x11_sync;
GLsync gpu_fence;
XSyncCounter xcounter;
XSyncAlarm xalarm;
......@@ -118,6 +119,8 @@ static void (*meta_gl_wait_sync) (GLsync sync,
static GLsync (*meta_gl_import_sync) (GLenum external_sync_type,
GLintptr external_sync,
GLbitfield flags);
static GLsync (*meta_gl_fence_sync) (GLenum condition,
GLbitfield flags);
static MetaSyncRing *
meta_sync_ring_get (void)
......@@ -224,6 +227,8 @@ load_required_symbols (void)
goto out;
if (!load_gl_symbol ("glImportSyncEXT", (void **) &meta_gl_import_sync))
goto out;
if (!load_gl_symbol ("glFenceSync", (void **) &meta_gl_fence_sync))
goto out;
success = TRUE;
out:
......@@ -238,7 +243,8 @@ meta_sync_insert (MetaSync *self)
XSyncTriggerFence (self->xdisplay, self->xfence);
XFlush (self->xdisplay);
meta_gl_wait_sync (self->glsync, 0, GL_TIMEOUT_IGNORED);
meta_gl_wait_sync (self->gl_x11_sync, 0, GL_TIMEOUT_IGNORED);
self->gpu_fence = meta_gl_fence_sync (GL_SYNC_GPU_COMMANDS_COMPLETE, 0);
self->state = META_SYNC_STATE_WAITING;
}
......@@ -255,9 +261,13 @@ meta_sync_check_update_finished (MetaSync *self,
status = GL_ALREADY_SIGNALED;
break;
case META_SYNC_STATE_WAITING:
status = meta_gl_client_wait_sync (self->glsync, 0, timeout);
status = meta_gl_client_wait_sync (self->gpu_fence, 0, timeout);
if (status == GL_ALREADY_SIGNALED || status == GL_CONDITION_SATISFIED)
self->state = META_SYNC_STATE_DONE;
{
self->state = META_SYNC_STATE_DONE;
meta_gl_delete_sync (self->gpu_fence);
self->gpu_fence = 0;
}
break;
default:
break;
......@@ -312,7 +322,8 @@ meta_sync_new (Display *xdisplay)
self->xdisplay = xdisplay;
self->xfence = XSyncCreateFence (xdisplay, DefaultRootWindow (xdisplay), FALSE);
self->glsync = meta_gl_import_sync (GL_SYNC_X11_FENCE_EXT, self->xfence, 0);
self->gl_x11_sync = meta_gl_import_sync (GL_SYNC_X11_FENCE_EXT, self->xfence, 0);
self->gpu_fence = 0;
self->xcounter = XSyncCreateCounter (xdisplay, SYNC_VALUE_ZERO);
......@@ -365,6 +376,8 @@ meta_sync_free (MetaSync *self)
switch (self->state)
{
case META_SYNC_STATE_WAITING:
meta_gl_delete_sync (self->gpu_fence);
break;
case META_SYNC_STATE_DONE:
/* nothing to do */
break;
......@@ -383,7 +396,7 @@ meta_sync_free (MetaSync *self)
break;
}
meta_gl_delete_sync (self->glsync);
meta_gl_delete_sync (self->gl_x11_sync);
XSyncDestroyFence (self->xdisplay, self->xfence);
XSyncDestroyCounter (self->xdisplay, self->xcounter);
XSyncDestroyAlarm (self->xdisplay, self->xalarm);
......
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