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wasm: fix CPU profiler deadlock #17877

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merged 2 commits into from
Apr 16, 2024
Merged

wasm: fix CPU profiler deadlock #17877

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75a1f2a
cmake: upgrade seastar
rockwotj Apr 16, 2024
a910869
wasm: fix CPU profiler hang
rockwotj Apr 16, 2024
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2 changes: 1 addition & 1 deletion cmake/dependencies.cmake
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Original file line number Diff line number Diff line change
Expand Up @@ -40,7 +40,7 @@ set(Seastar_API_LEVEL 6 CACHE STRING "" FORCE)
set(Seastar_CXX_FLAGS -Wno-error)
fetch_dep(seastar
REPO https://github.com/redpanda-data/seastar.git
TAG v23.3.x
TAG v24.1.x
PATCH_COMMAND sed -i "s/add_subdirectory (tests/# add_subdirectory (tests/g" CMakeLists.txt)

fetch_dep(avro
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19 changes: 18 additions & 1 deletion src/v/wasm/tests/wasm_transform_test.cc
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Expand Up @@ -11,10 +11,10 @@

#include "bytes/bytes.h"
#include "pandaproxy/schema_registry/types.h"
#include "serde/rw/rw.h"
#include "wasm/errc.h"
#include "wasm/tests/wasm_fixture.h"

#include <seastar/core/internal/cpu_profiler.hh>
#include <seastar/core/reactor.hh>

#include <absl/strings/str_cat.h>
Expand Down Expand Up @@ -134,3 +134,20 @@ TEST_F(WasmTestFixture, LogsAreEmitted) {
expected.append(reinterpret_cast<const char*>(bytes.data()), bytes.size());
EXPECT_THAT(log_lines(), ElementsAre(expected));
}

TEST_F(WasmTestFixture, WorksWithCpuProfiler) {
bool original_enabled = ss::engine().get_cpu_profiler_enabled();
std::chrono::nanoseconds original_period
= ss::engine().get_cpu_profiler_period();
ss::engine().set_cpu_profiler_enabled(true);
ss::engine().set_cpu_profiler_period(100us);
load_wasm("dynamic.wasm");
EXPECT_THROW(execute_command("loop", 0), wasm::wasm_exception);
ss::engine().set_cpu_profiler_enabled(original_enabled);
ss::engine().set_cpu_profiler_period(original_period);
std::vector<ss::cpu_profiler_trace> traces;
ss::engine().profiler_results(traces);
for (const auto& t : traces) {
std::cout << t.user_backtrace << "\n";
}
}
9 changes: 9 additions & 0 deletions src/v/wasm/wasmtime.cc
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Expand Up @@ -34,6 +34,7 @@

#include <seastar/core/align.hh>
#include <seastar/core/future.hh>
#include <seastar/core/internal/cpu_profiler.hh>
#include <seastar/core/posix.hh>
#include <seastar/core/sharded.hh>
#include <seastar/core/shared_ptr.hh>
Expand Down Expand Up @@ -599,7 +600,13 @@ class wasmtime_engine : public engine {
// Poll the call future to completion, yielding to the scheduler when
// the future yields.
auto start = ss::steady_clock_type::now();
// Disable profiling backtraces inside the VM - at the time of writing
// backtraces lead to segfaults causing deadlock in Seastar's signal
// handlers.
auto _ = ss::internal::scoped_disable_profile_temporarily();
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what is the comment mean on this object in seastar tree This is not reentrant?

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It means that it doesn't handle the case of nesting these RAII objects - when being destructed it doesn't set the flag to the original state, but unconditionally turns the flag off.

while (!wasmtime_call_future_poll(fut.get())) {
// Re-enable stacktraces before we yield control to the scheduler.
ss::internal::profiler_drop_stacktraces(false);
auto end = ss::steady_clock_type::now();
_probe.increment_cpu_time(end - start);
if (_pending_host_function) {
Expand All @@ -609,6 +616,8 @@ class wasmtime_engine : public engine {
co_await ss::coroutine::maybe_yield();
}
start = ss::steady_clock_type::now();
// Disable stacktraces as we enter back into Wasmtime
ss::internal::profiler_drop_stacktraces(true);
}
auto end = ss::steady_clock_type::now();
_probe.increment_cpu_time(end - start);
Expand Down
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