[Mesa-dev] [PATCH] loader/dri3: Improve dri3 thread-safety

Nicolai Hähnle nhaehnle at gmail.com
Tue Nov 21 10:50:09 UTC 2017


Hi Thomas,

On 20.11.2017 18:19, Thomas Hellstrom wrote:
> Is this a multithreaded test? Do you see the error with Ubuntu 17.10 + 
> Xorg?

The dEQP-GLES31 tests are all single-threaded.

I could finally test with the Ubuntu 17.10 on Xorg desktop on the same 
system (some other tests were running before in parallel), and indeed I 
don't get hangs there. Looks like it's due to Xwayland -- whether a bug 
in there or "just" some surprising interaction.

Cheers,
Nicolai


> 
> /Thomas
> 
> 
> On 11/20/2017 06:03 PM, Nicolai Hähnle wrote:
>> Hi Thomas,
>>
>> not actually a regression, but I am seeing hangs now with builds that 
>> include this patch when running the dEQP-GLES31 test. The backtrace is:
>>
>> #3  0x00007f947918262a in xcb_wait_for_special_event () from 
>> /usr/lib/x86_64-linux-gnu/libxcb.so.1
>> #4  0x00007f947c80984e in dri3_wait_for_event_locked 
>> (draw=0x61400000cc78)
>>     at ../../../mesa-src/src/loader/loader_dri3_helper.c:486
>> #5  0x00007f947c80b8e8 in loader_dri3_wait_for_sbc 
>> (draw=draw at entry=0x61400000cc78, target_sbc=61,
>>     target_sbc at entry=0, ust=ust at entry=0x7ffd1510d230, 
>> msc=msc at entry=0x7ffd1510d270,
>>     sbc=sbc at entry=0x7ffd1510d2b0) at 
>> ../../../mesa-src/src/loader/loader_dri3_helper.c:562
>> #6  0x00007f947c80fbe4 in loader_dri3_swapbuffer_barrier 
>> (draw=0x61400000cc78)
>>     at ../../../mesa-src/src/loader/loader_dri3_helper.c:1714
>> #7  0x00007f9474ced029 in dri_st_framebuffer_flush_swapbuffers 
>> (stctx=<optimized out>,
>>     stfbi=<optimized out>) at 
>> ../../../../../mesa-src/src/gallium/state_trackers/dri/dri_drawable.c:135
>> #8  0x00007f94747730c0 in st_finish (st=st at entry=0x62600000c100)
>>     at ../../../mesa-src/src/mesa/state_tracker/st_cb_flush.c:74
>> #9  0x00007f947477319f in st_glFinish (ctx=<optimized out>)
>>     at ../../../mesa-src/src/mesa/state_tracker/st_cb_flush.c:104
>> #10 0x00005595fe7d5cfd in glu::CallLogWrapper::glFinish 
>> (this=0x6030002b9b10)
>>     at 
>> /home/nha/amd/tests/deqp/framework/opengl/gluCallLogWrapper.inl:1166
>> #11 0x00005595fe3179dc in deqp::gles31::Functional::(anonymous 
>> namespace)::GeometryShaderRenderTest::renderWithContext 
>> (this=this at entry=0x612000000dc0, ctx=..., program=..., dstSurface=...)
>>     at 
>> /home/nha/amd/tests/deqp/modules/gles31/functional/es31fGeometryShaderTests.cpp:2145 
>>
>> #12 0x00005595fe31d2dc in deqp::gles31::Functional::(anonymous 
>> namespace)::GeometryShaderRenderTest::iterate (this=0x612000000dc0)
>>     at 
>> /home/nha/amd/tests/deqp/modules/gles31/functional/es31fGeometryShaderTests.cpp:1934 
>>
>> #13 0x00005595fe2d6cfe in deqp::gles31::TestCaseWrapper::iterate 
>> (this=0x60200000e950,
>>     testCase=<optimized out>) at 
>> /home/nha/amd/tests/deqp/modules/gles31/tes31TestPackage.cpp:76
>> #14 0x00005595fe7417d3 in tcu::TestSessionExecutor::iterateTestCase 
>> (this=this at entry=0x60e00000df60,
>>     testCase=0x612000000dc0)
>>
>> A command-line that fairly reliably causes the hang (but not always in 
>> the same subtest) is:
>>
>> /home/nha/amd/tests/deqp/build/modules/gles31/deqp-gles31 
>> --deqp-caselist="{dEQP-GLES31{functional{geometry_shading{input{basic_primitive{points,lines,line_loop,line_strip,triangles,triangle_strip,triangle_fan,lines_adjacency,line_strip_adjacency,triangles_adjacency},triangle_strip_adjacency{vertex_count_0,vertex_count_1,vertex_count_2,vertex_count_3,vertex_count_4,vertex_count_5,vertex_count_6,vertex_count_7,vertex_count_8,vertex_count_9,vertex_count_10,vertex_count_11,vertex_count_12}},conversion{triangles_to_points,lines_to_points,points_to_lines,triangles_to_lines,points_to_triangles,lines_to_triangles},emit{points_emit_0_end_0,points_emit_0_end_1,points_emit_1_end_1,points_emit_0_end_2,points_emit_1_end_2,line_strip_emit_0_end_0,line_strip_emit_0_end_1,line_strip_emit_1_end_1,line_strip_emit_2_end_1,line_strip_emit_0_end_2,line_strip_emit_1_end_2,line_strip_emit_2_end_2,line_strip_emit_2_end_2_emit_2_end_0,triangle_strip_emit_0_end_0,triangle_strip_emit_0_end_1,triangle_strip_emit_1_end_1,triangle_strip_emit_2_end_1,triangle_strip_emit_3_end_1,triangle_strip_emit_0_end_2,triangle_strip_emit_1_end_2,triangle_strip_emit_2_end_2,triangle_strip_emit_3_end_2,triangle_strip_emit_3_end_2_emit_3_end_0},varying{vertex_no_op_geometry_out_1,vertex_out_0_geometry_out_1,vertex_out_0_geometry_out_2,vertex_out_1_geometry_out_0,vertex_out_1_geometry_out_2},layered{render_with_default_layer_cubemap,render_with_default_layer_3d,render_with_default_layer_2d_array,render_with_default_layer_2d_multisample_array,render_to_one_cubemap,render_to_one_3d,render_to_one_2d_array,render_to_one_2d_multisample_array,render_to_all_cubemap,render_to_all_3d,render_to_all_2d_array,render_to_all_2d_multisample_array,render_different_to_cubemap,render_different_to_3d,render_different_to_2d_array,render_different_to_2d_multisample_array,fragment_layer_cubemap,fragment_layer_3d,fragment_layer_2d_array,fragment_layer_2d_multisample_array,layer_provoking_vertex_cubemap,layer_provoking_vertex_3d,layer_provoking_vertex_2d_array,layer_provoking_vertex_2d_multisample_array},instanced{geometry_1_invocations,geometry_2_invocations,geometry_8_invocations,geometry_32_invocations,geometry_max_invocations,geometry_output_different_2_invocations,geometry_output_different_8_invocations,geometry_output_different_32_invocations,geometry_output_different_max_invocations,invocation_per_layer_cubemap,invocation_per_layer_3d,invocation_per_layer_2d_array,invocation_per_layer_2d_multisample_array,multiple_layers_per_invocation_cubemap,multiple_layers_per_invocation_3d,multiple_layers_per_invocation_2d_array,multiple_layers_per_invocation_2d_multisample_array,invocation_output_vary_by_attribute,invocation_output_vary_by_uniform}}}}} 
>> " --deqp-visibility hidden
>>
>> This does not actually appear to be a regression in Mesa -- I started 
>> seeing it after updating to Ubuntu 17.10, so it may be related to 
>> Wayland or something else. Running the same setup on 17.04 (with Xorg) 
>> doesn't see the hangs. Disabling Gallium threading makes no 
>> difference. Any ideas what's going on?
>>
>> Thanks,
>> Nicolai
>>
>>
>> On 03.11.2017 12:02, Thomas Hellstrom wrote:
>>> 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://urldefense.proofpoint.com/v2/url?u=https-3A__bugs.freedesktop.org_show-5Fbug.cgi-3Fid-3D102358&d=DwIGaQ&c=uilaK90D4TOVoH58JNXRgQ&r=wnSlgOCqfpNS4d02vP68_E9q2BNMCwfD2OZ_6dCFVQQ&m=iDJcqIMFeVj6iTFCMMETKjNE_Ea04MZmEuaK4Qd9pVk&s=6HqE58_DXmtahSSCMcZlXab6GfjZ-S6fFA6ZkJKAprc&e= 
>>>
>>> Fixes: d5ba75f8881 "st/dri2 Plumb the flush_swapbuffer functionality 
>>> through to dri3"
>>> Signed-off-by: Thomas Hellstrom <thellstrom at vmware.com>
>>> ---
>>>   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 19ab581..7e6b8b2 100644
>>> --- a/src/loader/loader_dri3_helper.c
>>> +++ b/src/loader/loader_dri3_helper.c
>>> @@ -32,7 +32,6 @@
>>>     #include <X11/Xlib-xcb.h>
>>>   -#include <c11/threads.h>
>>>   #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 d3f4b0c..0dd37e9 100644
>>> --- a/src/loader/loader_dri3_helper.h
>>> +++ b/src/loader/loader_dri3_helper.h
>>> @@ -33,6 +33,7 @@
>>>     #include <GL/gl.h>
>>>   #include <GL/internal/dri_interface.h>
>>> +#include <c11/threads.h>
>>>     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
>>>
>>
>>
> 


-- 
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Aber vergiss niemals, wie sie sein sollte.


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