8000 thread_pthread.c: allocate sigaltstack before pthread_create · github/ruby@0256e4f · GitHub
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thread_pthread.c: allocate sigaltstack before pthread_create
A new (not-initialized-yet) pthread attempts to allocate sigaltstack by using xmalloc. It may cause GC, but because the thread is not initialized yet, ruby_native_thread_p() returns false, which leads to "[FATAL] failed to allocate memory" and exit. In fact, we can observe the error message in the log of OpenBSD CI: https://rubyci.org/logs/rubyci.s3.amazonaws.com/openbsd-current/ruby-master/log/20200306T083005Z.log.html.gz This changeset allocates sigaltstack before pthread is created.
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3 files changed

+27
-8
lines changed

3 files changed

+27
-8
lines changed

‎signal.c

Lines changed: 15 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -547,14 +547,25 @@ rb_sigaltstack_size(void)
547547
return size;
548548
}
549549

550+
static int rb_sigaltstack_size_value = 0;
551+
552+
void *
553+
rb_allocate_sigaltstack(void)
554+
{
555+
if (!rb_sigaltstack_size_value) {
556+
rb_sigaltstack_size_value = rb_sigaltstack_size();
557+
}
558+
return xmalloc(rb_sigaltstack_size_value);
559+
}
560+
550561
/* alternate stack for SIGSEGV */
551562
void *
552-
rb_register_sigaltstack(void)
563+
rb_register_sigaltstack(void *altstack)
553564
{
554565
stack_t newSS, oldSS;
555566

556-
newSS.ss_size = rb_sigaltstack_size();
557-
newSS.ss_sp = xmalloc(newSS.ss_size);
567+
newSS.ss_size = rb_sigaltstack_size_value;
568+
newSS.ss_sp = altstack;
558569
newSS.ss_flags = 0;
559570

560571
sigaltstack(&newSS, &oldSS); /* ignore error. */
@@ -1561,7 +1572,7 @@ Init_signal(void)
15611572
force_install_sighandler(SIGILL, (sighandler_t)sigill, &default_sigill_handler);
15621573
#endif
15631574
#ifdef SIGSEGV
1564-
RB_ALTSTACK_INIT(GET_VM()->main_altstack);
1575+
RB_ALTSTACK_INIT(GET_VM()->main_altstack, rb_allocate_sigaltstack());
15651576
force_install_sighandler(SIGSEGV, (sighandler_t)sigsegv, &default_sigsegv_handler);
15661577
#endif
15671578
}

‎thread_pthread.c

Lines changed: 4 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -950,7 +950,7 @@ static void *
950950
thread_start_func_1(void *th_ptr)
951951
{
952952
rb_thread_t *th = th_ptr;
953-
RB_ALTSTACK_INIT(void *altstack);
953+
RB_ALTSTACK_INIT(void *altstack, th->altstack);
954954
#if USE_THREAD_CACHE
955955
thread_start:
956956
#endif
@@ -1099,6 +1099,9 @@ native_thread_create(rb_thread_t *th)
10991099
const size_t stack_size = th->vm->default_params.thread_machine_stack_size + th->vm->default_params.thread_vm_stack_size;
11001100
const size_t space = space_size(stack_size);
11011101

1102+
#ifdef USE_SIGALTSTACK
1103+
th->altstack = rb_allocate_sigaltstack();
1104+
#endif
11021105
th->ec->machine.stack_maxsize = stack_size - space;
11031106

11041107
CHECK_ERR(pthread_attr_init(&attr));

‎vm_core.h

Lines changed: 8 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -141,12 +141,13 @@
141141

142142
#if defined(SIGSEGV) && defined(HAVE_SIGALTSTACK) && defined(SA_SIGINFO) && !defined(__NetBSD__)
143143
# define USE_SIGALTSTACK
144-
void *rb_register_sigaltstack(void);
145-
# define RB_ALTSTACK_INIT(var) var = rb_register_sigaltstack()
144+
void *rb_allocate_sigaltstack(void);
145+
void *rb_register_sigaltstack(void *);
146+
# define RB_ALTSTACK_INIT(var, altstack) var = rb_register_sigaltstack(altstack)
146147
# define RB_ALTSTACK_FREE(var) xfree(var)
147148
# define RB_ALTSTACK(var) var
148149
#else /* noop */
149-
# define RB_ALTSTACK_INIT(var)
150+
# define RB_ALTSTACK_INIT(var, altstack)
150151
# define RB_ALTSTACK_FREE(var)
151152
# define RB_ALTSTACK(var) (0)
152153
#endif
@@ -974,6 +975,10 @@ typedef struct rb_thread_struct {
974975
/* misc */
975976
VALUE name;
976977

978+
#ifdef USE_SIGALTSTACK
979+
void *altstack;
980+
#endif
981+
977982
} rb_thread_t;
978983

979984
typedef enum {

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