From c68b7b1cac2f731cc35e99902bdc51655da804f0 Mon Sep 17 00:00:00 2001 From: Azat Khuzhin Date: Mon, 22 Jun 2026 12:47:46 +0200 Subject: [PATCH] test: add `tcache_fiber_migration` standalone LTO reproducer Exercises the tsd thread-pointer hoisting bug: ucontext fibers do free/swapcontext/malloc in one frame on a worker pool, so a fiber routinely resumes on a different OS thread; under whole-program LTO the inlined fastpath then frees/allocs against the previous thread's tcache and crashes. It is a standalone program (no test harness, so it can be static-linked without symbol clashes), calling jemalloc via JEMALLOC_MANGLE and linked statically with --whole-archive so the allocator inlines next to the swapcontext. Built only when -flto is in the build flags -- without LTO the allocator is not inlined and the bug cannot reproduce, so the test would be a meaningless always-pass -- and gated on ELF + static + have_ucontext (a configure link test, since musl declares but does not implement getcontext/makecontext/swapcontext). Co-Authored-By: Claude Opus 4.8 (1M context) --- Makefile.in | 27 +++++ configure.ac | 19 +++ test/integration/tcache_fiber_migration.c | 135 ++++++++++++++++++++++ 3 files changed, 181 insertions(+) create mode 100644 test/integration/tcache_fiber_migration.c diff --git a/Makefile.in b/Makefile.in index 16d6a820..d2a0d91d 100644 --- a/Makefile.in +++ b/Makefile.in @@ -59,6 +59,7 @@ enable_autogen := @enable_autogen@ enable_doc := @enable_doc@ enable_shared := @enable_shared@ enable_static := @enable_static@ +have_ucontext := @have_ucontext@ enable_prof := @enable_prof@ enable_zone_allocator := @enable_zone_allocator@ enable_experimental_smallocx := @enable_experimental_smallocx@ @@ -345,6 +346,24 @@ ifeq (@enable_experimental_smallocx@, 1) TESTS_INTEGRATION += \ $(srcroot)test/integration/smallocx.c endif +# tcache_fiber_migration is a standalone LTO reproducer (issue #2890): the +# dedicated rule below links it against the static archive (--whole-archive) so +# the allocator fastpath inlines next to the swapcontext. It needs the static +# archive, GNU-ld --whole-archive semantics (the ELF gate), and working +# ucontext fibers -- have_ucontext is a configure link test because musl +# declares getcontext/makecontext/swapcontext but does not implement them, so +# the ELF gate alone would break `make check` on Alpine/musl. Built only when +# the build uses LTO (-flto in CFLAGS): without inlining across the swapcontext +# the bug cannot reproduce. +ifeq (elf, $(ABI)) +ifeq ($(enable_static), 1) +ifeq (1, $(have_ucontext)) +ifneq (,$(findstring -flto,$(CFLAGS))) +TESTS_INTEGRATION += $(srcroot)test/integration/tcache_fiber_migration.c +endif +endif +endif +endif ifeq (@enable_cxx@, 1) CPP_SRCS := $(srcroot)src/jemalloc_cpp.cpp TESTS_INTEGRATION_CPP := $(srcroot)test/integration/cpp/basic.cpp @@ -578,6 +597,14 @@ $(objroot)test/integration/%$(EXE): $(objroot)test/integration/%.$(O) $(C_TESTLI @mkdir -p $(@D) $(CC) $(TEST_LD_MODE) $(LDTARGET) $(filter %.$(O),$^) $(call RPATH,$(objroot)lib) $(LJEMALLOC) $(LDFLAGS) $(filter-out -lm,$(filter -lrt -pthread -lstdc++,$(LIBS))) $(LM) $(EXTRA_LDFLAGS) +# tcache_fiber_migration (issue #2890) must inline the allocator next to the +# swapcontext, so link jemalloc statically (--whole-archive), without the test +# harness/shared lib; whole-program LTO (from the build's flags) does the +# inlining. Explicit rule -- overrides the generic integration rule above. +$(objroot)test/integration/tcache_fiber_migration$(EXE): $(objroot)test/integration/tcache_fiber_migration.$(O) $(objroot)lib/$(LIBJEMALLOC).$(A) + @mkdir -p $(@D) + $(CC) $(LDTARGET) $(objroot)test/integration/tcache_fiber_migration.$(O) -Wl,--whole-archive $(objroot)lib/$(LIBJEMALLOC).$(A) -Wl,--no-whole-archive $(LDFLAGS) -pthread $(filter-out -lm,$(LIBS)) $(LM) $(EXTRA_LDFLAGS) + $(objroot)test/integration/cpp/%$(EXE): $(objroot)test/integration/cpp/%.$(O) $(C_TESTLIB_INTEGRATION_OBJS) $(C_UTIL_INTEGRATION_OBJS) $(objroot)lib/$(LIBJEMALLOC).$(IMPORTLIB) @mkdir -p $(@D) $(CXX) $(LDTARGET) $(filter %.$(O),$^) $(call RPATH,$(objroot)lib) $(objroot)lib/$(LIBJEMALLOC).$(IMPORTLIB) $(LDFLAGS) $(filter-out -lm,$(LIBS)) -lm $(EXTRA_LDFLAGS) diff --git a/configure.ac b/configure.ac index 6532af1c..12af2e99 100644 --- a/configure.ac +++ b/configure.ac @@ -1217,6 +1217,25 @@ if test "$enable_shared$enable_static" = "00" ; then AC_MSG_ERROR([Please enable one of shared or static builds]) fi +dnl Whether ucontext fibers (getcontext/makecontext/swapcontext) actually link. +dnl musl declares them in but exports no implementation, so a +dnl link test is required -- a header check would pass and then fail to link. +dnl Used to gate the tcache_fiber_migration test. +JE_COMPILABLE([ucontext], [ +#include +], [ + ucontext_t uc, ret; + getcontext(&uc); + makecontext(&uc, (void (*)(void))0, 0); + swapcontext(&ret, &uc); +], [je_cv_ucontext]) +if test "x${je_cv_ucontext}" = "xyes" ; then + have_ucontext="1" +else + have_ucontext="0" +fi +AC_SUBST([have_ucontext]) + dnl Perform no name mangling by default. AC_ARG_WITH([mangling], [AS_HELP_STRING([--with-mangling=], [Mangle symbols in ])], diff --git a/test/integration/tcache_fiber_migration.c b/test/integration/tcache_fiber_migration.c new file mode 100644 index 00000000..27698d37 --- /dev/null +++ b/test/integration/tcache_fiber_migration.c @@ -0,0 +1,135 @@ +/* + * Regression test for issue #2890: under whole-program LTO the inlined allocator + * fastpath caches the TLS-derived tcache base in a register across a + * swapcontext, so a fiber resumed on another OS thread uses the previous + * thread's tcache -> heap corruption. See JEMALLOC_TLS_ADDR in tsd_internals.h. + * + * Standalone (no test harness, so it can be static-linked), calling jemalloc via + * JEMALLOC_MANGLE -- it rewrites malloc/free to jemalloc's configured-prefix + * symbols, so the calls bind to and inline the static allocator, not libc's + * wrappers. Reproduces only with the allocator inlined next to the swapcontext + * (a static --whole-archive link plus whole-program LTO), so the Makefile builds + * it only when -flto is in the build flags. + */ +#include +#include +#include + +#define JEMALLOC_MANGLE +#include + +enum { + num_fibers = 128, + num_workers = 8, + ops_per_fiber = 20 * 1000, + fiber_stack_size = 1 << 16, + ready_queue_capacity = 512 /* power of two, > num_fibers */ +}; + +static ucontext_t fiber_context[num_fibers]; +/* Scheduler context to switch back to when a fiber yields; the resuming worker + * writes its own context here, so this changes when the fiber migrates. */ +static ucontext_t *return_context[num_fibers]; +static unsigned fiber_remaining_ops[num_fibers]; +static bool fiber_done[num_fibers]; + +static unsigned ready_queue[ready_queue_capacity]; +static unsigned ready_queue_head; +static unsigned ready_queue_tail; +static unsigned live_fibers; +static pthread_mutex_t queue_mtx = PTHREAD_MUTEX_INITIALIZER; + +static void +push_ready_fiber(unsigned id) { + pthread_mutex_lock(&queue_mtx); + ready_queue[ready_queue_head++ & (ready_queue_capacity - 1)] = id; + pthread_mutex_unlock(&queue_mtx); +} + +/* Returns a ready fiber id, -1 if none ready now, or -2 if all have finished. */ +static int +pop_ready_fiber(void) { + int id; + pthread_mutex_lock(&queue_mtx); + if (live_fibers == 0) { + id = -2; + } else if (ready_queue_tail != ready_queue_head) { + id = (int)ready_queue[ready_queue_tail++ & (ready_queue_capacity - 1)]; + } else { + id = -1; + } + pthread_mutex_unlock(&queue_mtx); + return id; +} + +static void +fiber_run(int id) { + void *p = malloc(64); + while (fiber_remaining_ops[id] > 0) { + fiber_remaining_ops[id]--; + free(p); /* push to the CURRENT thread's tcache */ + /* Yield; may be resumed on a different worker thread. */ + swapcontext(&fiber_context[id], return_context[id]); + p = malloc(64); /* pop; must come from the NEW thread's tcache */ + *(char *)p = (char)id; + } + free(p); + pthread_mutex_lock(&queue_mtx); + fiber_done[id] = true; + live_fibers--; + pthread_mutex_unlock(&queue_mtx); + swapcontext(&fiber_context[id], return_context[id]); +} + +static void * +worker_thread(void *arg) { + ucontext_t scheduler_context; + (void)arg; + for (;;) { + int id = pop_ready_fiber(); + if (id == -2) { + break; + } + if (id < 0) { + continue; + } + return_context[id] = &scheduler_context; + swapcontext(&scheduler_context, &fiber_context[id]); + if (!fiber_done[id]) { + push_ready_fiber((unsigned)id); + } + } + return NULL; +} + +int +main(void) { + void *stacks[num_fibers]; + pthread_t threads[num_workers]; + unsigned i; + + live_fibers = num_fibers; + for (i = 0; i < num_fibers; i++) { + stacks[i] = malloc(fiber_stack_size); + fiber_remaining_ops[i] = ops_per_fiber; + getcontext(&fiber_context[i]); + fiber_context[i].uc_stack.ss_sp = stacks[i]; + fiber_context[i].uc_stack.ss_size = fiber_stack_size; + fiber_context[i].uc_link = NULL; + makecontext(&fiber_context[i], (void (*)(void))fiber_run, 1, (int)i); + push_ready_fiber(i); + } + + for (i = 0; i < num_workers; i++) { + pthread_create(&threads[i], NULL, worker_thread, NULL); + } + for (i = 0; i < num_workers; i++) { + pthread_join(threads[i], NULL); + } + for (i = 0; i < num_fibers; i++) { + free(stacks[i]); + } + + /* Completing without a tcache-corruption crash is success. */ + return live_fibers == 0 ? 0 : 1; +}