[Tarantool-patches] [PATCH luajit] Fix interaction between profiler hooks and finalizers.
Sergey Kaplun
skaplun at tarantool.org
Mon Jun 6 16:35:28 MSK 2022
From: Mike Pall <mike>
Thanks to Julien Desgats.
(cherry picked from commit 92fa45f9eb5d9aa732c6b972a85c26120d7612b4)
Embedded LuaJIT profiler uses the following approach:
* Create trigger on timer signals, which set `HOOK_PROFILE` flag on
`g->hookmask` (if not set already) and update all BC instructions
dispatch.
* When any of instruction is executed, callback set by user on profiler
initialize is called. After the dispatch table updated again to
the old static values, and flags are reset.
* `HOOK_PROFILE` flag will set again and dispatch will updated at the next
tick of the timer.
Before call to __gc finalizer the old hookmask is saved to be restored
later. When the second step is happening on call of __gc metamethod
`HOOK_PROFILE` flag is reset. But right after that the old hook
disposition (with `HOOK_PROFILE`) is restored, when we leaving
`gc_call_finalizer()` without updating the dispatch table, so the
profiler callback is never called again.
This patch updates dispatch table right after hooks manipulation in
`gc_call_finalizer()` and prevent ticks influence inside finalizer
calls.
Sergey Kaplun:
* added the description and the test for the problem
Part of tarantool/tarantool#6548
---
Side note: PR has 2 extra commits because the tarantool/luajit master
(tarantool branch) isn't bumped in the tarantool yet.
Branch: https://github.com/tarantool/luajit/tree/skaplun/lj-512-profiler-hook-finalizers-full-ci
Tarantool PR: https://github.com/tarantool/tarantool/pull/7237
Related issues:
* https://github.com/LuaJIT/LuaJIT/issues/512
* https://github.com/tarantool/tarantool/issues/6548
src/lj_gc.c | 2 ++
src/lj_obj.h | 3 +-
src/lj_profile.c | 2 +-
.../lj-512-profiler-hook-finalizers.test.lua | 31 +++++++++++++++++++
4 files changed, 36 insertions(+), 2 deletions(-)
create mode 100644 test/tarantool-tests/lj-512-profiler-hook-finalizers.test.lua
diff --git a/src/lj_gc.c b/src/lj_gc.c
index 7f0ec896..29387a48 100644
--- a/src/lj_gc.c
+++ b/src/lj_gc.c
@@ -493,6 +493,7 @@ static void gc_call_finalizer(global_State *g, lua_State *L,
TValue *top;
lj_trace_abort(g);
hook_entergc(g); /* Disable hooks and new traces during __gc. */
+ if (LJ_HASPROFILE && (oldh & HOOK_PROFILE)) lj_dispatch_update(g);
g->gc.threshold = LJ_MAX_MEM; /* Prevent GC steps. */
top = L->top;
copyTV(L, top++, mo);
@@ -501,6 +502,7 @@ static void gc_call_finalizer(global_State *g, lua_State *L,
L->top = top+1;
errcode = lj_vm_pcall(L, top, 1+0, -1); /* Stack: |mo|o| -> | */
hook_restore(g, oldh);
+ if (LJ_HASPROFILE && (oldh & HOOK_PROFILE)) lj_dispatch_update(g);
g->gc.threshold = oldt; /* Restore GC threshold. */
if (errcode)
lj_err_throw(L, errcode); /* Propagate errors. */
diff --git a/src/lj_obj.h b/src/lj_obj.h
index 197d735a..d1451c3a 100644
--- a/src/lj_obj.h
+++ b/src/lj_obj.h
@@ -692,7 +692,8 @@ typedef struct global_State {
#define HOOK_PROFILE 0x80
#define hook_active(g) ((g)->hookmask & HOOK_ACTIVE)
#define hook_enter(g) ((g)->hookmask |= HOOK_ACTIVE)
-#define hook_entergc(g) ((g)->hookmask |= (HOOK_ACTIVE|HOOK_GC))
+#define hook_entergc(g) \
+ ((g)->hookmask = ((g)->hookmask | (HOOK_ACTIVE|HOOK_GC)) & ~HOOK_PROFILE)
#define hook_vmevent(g) ((g)->hookmask |= (HOOK_ACTIVE|HOOK_VMEVENT))
#define hook_leave(g) ((g)->hookmask &= ~HOOK_ACTIVE)
#define hook_save(g) ((g)->hookmask & ~HOOK_EVENTMASK)
diff --git a/src/lj_profile.c b/src/lj_profile.c
index 4412d68b..896d8f46 100644
--- a/src/lj_profile.c
+++ b/src/lj_profile.c
@@ -106,7 +106,7 @@ static void profile_trigger(ProfileState *ps)
profile_lock(ps);
ps->samples++; /* Always increment number of samples. */
mask = g->hookmask;
- if (!(mask & (HOOK_PROFILE|HOOK_VMEVENT))) { /* Set profile hook. */
+ if (!(mask & (HOOK_PROFILE|HOOK_VMEVENT|HOOK_GC))) { /* Set profile hook. */
int st = g->vmstate;
ps->vmstate = st >= 0 ? 'N' :
st == ~LJ_VMST_INTERP ? 'I' :
diff --git a/test/tarantool-tests/lj-512-profiler-hook-finalizers.test.lua b/test/tarantool-tests/lj-512-profiler-hook-finalizers.test.lua
new file mode 100644
index 00000000..4b6aabb7
--- /dev/null
+++ b/test/tarantool-tests/lj-512-profiler-hook-finalizers.test.lua
@@ -0,0 +1,31 @@
+local tap = require('tap')
+local profile = require('jit.profile')
+
+local test = tap.test('lj-512-profiler-hook-finalizers')
+test:plan(1)
+
+-- Sampling interval in ms.
+local INTERVAL = 10
+
+local nsamples = 0
+profile.start('li' .. tostring(INTERVAL), function()
+ nsamples = nsamples + 1
+end)
+
+local start = os.clock()
+for _ = 1, 1e6 do
+ getmetatable(newproxy(true)).__gc = function() end
+end
+local finish = os.clock()
+
+profile.stop()
+
+-- XXX: The bug is occured as stopping of callbacks invocation,
+-- when a new tick strikes inside `gc_call_finalizer()`.
+-- The amount of successfull callbacks isn't stable (2-15).
+-- So, assume that amount of profiling samples should be at least
+-- more than 0.5 intervals of time during sampling.
+test:ok(nsamples >= 0.5 * (finish - start) * 1e3 / INTERVAL,
+ 'profiler sampling')
+
+os.exit(test:check() and 0 or 1)
--
2.34.1
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