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Appending a regular command list to an idle immediate command list aborts in LinearStream::getSpace when a UC tag update is pending

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Dal 17/10/2026.

  • #1028 di @maleadt — aperta

Valutazione

Difficoltà
2/5
Tempo stimato
1-3 ore
Idoneità per principianti
20/100
Tipo di issue
Bug
Chiarezza
Specificata chiaramente
Stato di attività
Ferma
Stack tecnologico
cpp
Ambito
backend

Direzione di ricerca

Start in shared/source/command_stream/command_stream_receiver_hw_base.inl, where flushTaskHeapful emits the UC tag update, and compare it with the nearby barrier handling and the BCS path described in the issue. Add or inspect the ULT for appending a regular list to an idle in-order immediate list with a pending tag update; done means the tag update uses the epilogue stream when present and the reproducer no longer aborts. A linked pull request is already open.

Scritto dal modello di indicizzazione a partire dal testo della issue.

Descrizione

Summary

Appending a regular command list to an in-order immediate command list with zeCommandListImmediateAppendCommandListsExp aborts the process if the immediate list is idle and the CSR has a pending UC tag update:

Abort was called at 90 line in file:
.../shared/source/command_stream/linear_stream.h

(line 91 on master)

NEO::abortUnrecoverable(int, char const*)
NEO::MemorySynchronizationCommands<NEO::Gen12LpFamily>::addBarrierWithPostSyncOperation(...)
NEO::CommandStreamReceiverHw<NEO::Gen12LpFamily>::emitTagUpdateWithoutDCFlush(NEO::LinearStream&)
NEO::CommandStreamReceiverHw<NEO::Gen12LpFamily>::flushTaskHeapful(...)
NEO::CommandStreamReceiverHw<NEO::Gen12LpFamily>::flushTask(...)
L0::CommandListCoreFamilyImmediate<(GFXCORE_FAMILY)18>::flushRegularTask(...)
L0::CommandListCoreFamilyImmediate<(GFXCORE_FAMILY)18>::executeCommandListImmediateWithFlushTaskImpl(...)
L0::CommandListCoreFamilyImmediate<(GFXCORE_FAMILY)18>::flushImmediate(...)
L0::CommandListCoreFamilyImmediate<(GFXCORE_FAMILY)18>::appendCommandLists(...)
L0::zeCommandListImmediateAppendCommandListsExp(...)

It shows up as a sporadic abort in applications that submit work in batches of regular command lists. The reproducer below makes it deterministic.

Cause

Two features meet here:

  1. When appendCommandLists has nothing to dispatch from the queue (the immediate list is idle, so there is no wait or implicit dependency), and the command list's batch buffer is dispatched as primary, the queue submits the regular list's first command buffer directly. It wraps that buffer in firstCmdListStream and marks it full (cmdqueue_hw.inl#L1567-L1572): 
    this->firstCmdListStream.replaceBuffer(cmdListFirstCmdBuffer->getUnderlyingBuffer(), firstCmdBufferAlignedSize);
this->firstCmdListStream.getSpace(firstCmdBufferAlignedSize);
this->startingCmdBuffer = &this->firstCmdListStream;
    The immediate list's own stream is passed along as dispatchFlags.optionalEpilogueCmdStream, for the commands that follow the task.
  2. Since c78c1515de / 64b79723cc ("reuse cmd buffer without dc flush", 25.44), ensureCommandBufferAllocation sets ucResourceRequiresTagUpdate whenever the CSR's command buffer is replaced (command_stream_receiver.cpp#L372). The next flushTaskHeapful then emits the tag update into the task stream (command_stream_receiver_hw_base.inl#L469-L471): 
    if (this->ucResourceRequiresTagUpdate) {
    this->emitTagUpdateWithoutDCFlush(commandStreamTask);
}

When the flush after a CSR command buffer replacement is such a direct submission, the PIPE_CONTROL goes into the full firstCmdListStream, and LinearStream::getSpace hits UNRECOVERABLE_IF(sizeUsed + size > maxAvailableSpace).

I confirmed this with a debugger: at the abort, the task stream passed to flushTaskHeapful has getUsed() == getMaxAvailableSpace() (312 of 312 bytes, i.e. a small regular list's buffer), and CommandStreamReceiver::releaseCommandBufferAllocation ran during the preceding flush.

The other epilogue commands already account for this. The barrier with post-sync a few lines further down in flushTaskHeapful (#L481) and the UC tag update in flushBcsTask (#L228-L232) both write to optionalEpilogueCmdStream when one is set. Only the UC tag update in flushTaskHeapful uses the task stream unconditionally.

Reproducer
repro.c 
// Appending a regular command list to an idle in-order immediate command list aborts in
// LinearStream::getSpace once the CSR has a pending UC tag update.
//
// cc -O2 -o repro repro.c -I<level-zero include> -L<loader dir> -lze_loader
// ./repro [iterations]

#include <level_zero/ze_api.h>
#include <stdio.h>
#include <stdlib.h>

#define CHECK(call)                                                            \
    do {                                                                       \
        ze_result_t res_ = (call);                                             \
        if (res_ != ZE_RESULT_SUCCESS) {                                       \
            fprintf(stderr, "%s failed: 0x%x (line %d)\n", #call, res_,        \
                    __LINE__);                                                 \
            exit(1);                                                           \
        }                                                                      \
    } while (0)

int main(int argc, char **argv) {
    int iterations = argc > 1 ? atoi(argv[1]) : 10000;

    CHECK(zeInit(0));
    uint32_t count = 1;
    ze_driver_handle_t driver;
    CHECK(zeDriverGet(&count, &driver));
    count = 1;
    ze_device_handle_t device;
    CHECK(zeDeviceGet(driver, &count, &device));

    ze_device_properties_t props = {ZE_STRUCTURE_TYPE_DEVICE_PROPERTIES};
    CHECK(zeDeviceGetProperties(device, &props));
    printf("device: %s\n", props.name);

    ze_context_desc_t context_desc = {ZE_STRUCTURE_TYPE_CONTEXT_DESC};
    ze_context_handle_t context;
    CHECK(zeContextCreate(driver, &context_desc, &context));

    // compute engine group
    uint32_t ngroups = 0;
    CHECK(zeDeviceGetCommandQueueGroupProperties(device, &ngroups, NULL));
    ze_command_queue_group_properties_t groups[16];
    for (uint32_t i = 0; i < ngroups && i < 16; i++)
        groups[i] = (ze_command_queue_group_properties_t){
            ZE_STRUCTURE_TYPE_COMMAND_QUEUE_GROUP_PROPERTIES};
    CHECK(zeDeviceGetCommandQueueGroupProperties(device, &ngroups, groups));
    uint32_t ordinal = 0;
    for (uint32_t i = 0; i < ngroups; i++)
        if (groups[i].flags & ZE_COMMAND_QUEUE_GROUP_PROPERTY_FLAG_COMPUTE) {
            ordinal = i;
            break;
        }

    ze_command_queue_desc_t queue_desc = {ZE_STRUCTURE_TYPE_COMMAND_QUEUE_DESC};
    queue_desc.ordinal = ordinal;
    queue_desc.flags = ZE_COMMAND_QUEUE_FLAG_IN_ORDER;
    queue_desc.mode = ZE_COMMAND_QUEUE_MODE_ASYNCHRONOUS;
    ze_command_list_handle_t immediate;
    CHECK(zeCommandListCreateImmediate(context, device, &queue_desc, &immediate));

    ze_command_list_desc_t list_desc = {ZE_STRUCTURE_TYPE_COMMAND_LIST_DESC};
    list_desc.commandQueueGroupOrdinal = ordinal;
    list_desc.flags = ZE_COMMAND_LIST_FLAG_IN_ORDER;
    ze_command_list_handle_t regular;
    CHECK(zeCommandListCreate(context, device, &list_desc, &regular));

    const size_t size = 4096;
    ze_device_mem_alloc_desc_t mem_desc = {ZE_STRUCTURE_TYPE_DEVICE_MEM_ALLOC_DESC};
    void *a, *b;
    CHECK(zeMemAllocDevice(context, &mem_desc, size, 64, device, &a));
    CHECK(zeMemAllocDevice(context, &mem_desc, size, 64, device, &b));

    for (int i = 0; i < iterations; i++) {
        // work on the immediate list, which consumes space in the CSR's command buffer;
        // when that buffer is replaced, the CSR schedules a UC tag update for its next flush
        CHECK(zeCommandListAppendMemoryCopy(immediate, b, a, size, NULL, 0, NULL));
        CHECK(zeCommandListHostSynchronize(immediate, UINT64_MAX));

        // append a regular command list to the now idle immediate list: with nothing to
        // dispatch from the queue, the regular list's own buffer becomes the batch buffer
        CHECK(zeCommandListReset(regular));
        for (int j = 0; j < 4; j++) {
            uint32_t pattern = i + j;
            CHECK(zeCommandListAppendMemoryFill(regular, a, &pattern, sizeof(pattern),
                                                size, NULL, 0, NULL));
        }
        CHECK(zeCommandListClose(regular));
        CHECK(zeCommandListImmediateAppendCommandListsExp(immediate, 1, &regular, NULL,
                                                          0, NULL));
        CHECK(zeCommandListHostSynchronize(immediate, UINT64_MAX));

        if ((i + 1) % 1000 == 0)
            printf("%d iterations\n", i + 1);
    }

    printf("done\n");
    CHECK(zeMemFree(context, a));
    CHECK(zeMemFree(context, b));
    CHECK(zeCommandListDestroy(regular));
    CHECK(zeCommandListDestroy(immediate));
    CHECK(zeContextDestroy(context));
    return 0;
}

$ cc -O2 -o repro repro.c -lze_loader
$ ./repro 20000
device: Intel(R) Iris(R) Xe Graphics
Abort was called at 90 line in file:
/workspace/srcdir/compute-runtime/shared/source/command_stream/linear_stream.h
Aborted

It aborts within the first thousand iterations, on every run. The memory copy on the immediate list is there to consume CSR command buffer space, so that the buffer is eventually replaced. The host synchronization before the append makes the immediate list idle, which selects the direct submission of the regular list.

Environment
  • Intel Iris Xe Graphics (Tiger Lake GT2, 8086:9a49), i915, Linux 6.12 (Debian 13)
  • compute-runtime 26.35.39758.10 (release build), IGC 2.41.5, gmmlib 22.10.0
  • The code involved is unchanged on master (7582a08ed2).
  • 25.18 (LTS) is not affected, since it predates the UC tag update.
Fix

Emit the tag update into the epilogue stream when there is one, as the barrier and the BCS path already do. I'll open a PR with that change and a ULT.

Downstream, this crashes the oneAPI.jl test suite, which submits kernel launches in batches of regular command lists (JuliaGPU/oneAPI.jl#693, failures seen on JuliaGPU/oneAPI.jl#707).

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