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

Thomas Hellstrom thellstrom at vmware.com
Mon Nov 20 17:19:46 UTC 2017


Hi, Nicholai,

Is this a multithreaded test? Do you see the error with Ubuntu 17.10 + Xorg?

/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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