[musl] [PATCH v2] MT fork

[Rich Felker <dalias@libc.org>]

[-- Attachment #1: Type: text/plain, Size: 498 bytes --]

On Tue, Oct 27, 2020 at 05:17:35PM -0400, Rich Felker wrote:
> > > 
> > > Will follow up with draft patch for testing.
> > 
> > Patch attached. It should suffice for testing and review of whether
> > there are any locks/state I overlooked. It could possibly be made less
> > ugly too.
> > [...]
> 
> Another bug:
> [...]

And an updated version of the patch with both previously reported bugs
fixed, for the purpose of users/distros wanting to test without
manually fixing up the patch. Attached.


[-- Attachment #2: mt-fork-v2.diff --]
[-- Type: text/plain, Size: 11289 bytes --]

diff --git a/ldso/dynlink.c b/ldso/dynlink.c
index f9ac0100..acd8e59b 100644
--- a/ldso/dynlink.c
+++ b/ldso/dynlink.c
@@ -21,6 +21,7 @@
 #include <semaphore.h>
 #include <sys/membarrier.h>
 #include "pthread_impl.h"
+#include "fork_impl.h"
 #include "libc.h"
 #include "dynlink.h"
 
@@ -1404,6 +1405,17 @@ void __libc_exit_fini()
 	}
 }
 
+void __ldso_atfork(int who)
+{
+	if (who<0) {
+		pthread_rwlock_wrlock(&lock);
+		pthread_mutex_lock(&init_fini_lock);
+	} else {
+		pthread_mutex_unlock(&init_fini_lock);
+		pthread_rwlock_unlock(&lock);
+	}
+}
+
 static struct dso **queue_ctors(struct dso *dso)
 {
 	size_t cnt, qpos, spos, i;
@@ -1462,6 +1474,13 @@ static struct dso **queue_ctors(struct dso *dso)
 	}
 	queue[qpos] = 0;
 	for (i=0; i<qpos; i++) queue[i]->mark = 0;
+	for (i=0; i<qpos; i++)
+		if (queue[i]->ctor_visitor && queue[i]->ctor_visitor->tid < 0) {
+			error("State of %s is inconsistent due to multithreaded fork\n",
+				queue[i]->name);
+			free(queue);
+			if (runtime) longjmp(*rtld_fail, 1);
+		}
 
 	return queue;
 }
diff --git a/src/exit/at_quick_exit.c b/src/exit/at_quick_exit.c
index d3ce6522..e4b5d78d 100644
--- a/src/exit/at_quick_exit.c
+++ b/src/exit/at_quick_exit.c
@@ -1,12 +1,14 @@
 #include <stdlib.h>
 #include "libc.h"
 #include "lock.h"
+#include "fork_impl.h"
 
 #define COUNT 32
 
 static void (*funcs[COUNT])(void);
 static int count;
 static volatile int lock[1];
+volatile int *const __at_quick_exit_lockptr = lock;
 
 void __funcs_on_quick_exit()
 {
diff --git a/src/exit/atexit.c b/src/exit/atexit.c
index 160d277a..2804a1d7 100644
--- a/src/exit/atexit.c
+++ b/src/exit/atexit.c
@@ -2,6 +2,7 @@
 #include <stdint.h>
 #include "libc.h"
 #include "lock.h"
+#include "fork_impl.h"
 
 /* Ensure that at least 32 atexit handlers can be registered without malloc */
 #define COUNT 32
@@ -15,6 +16,7 @@ static struct fl
 
 static int slot;
 static volatile int lock[1];
+volatile int *const __atexit_lockptr = lock;
 
 void __funcs_on_exit()
 {
diff --git a/src/internal/fork_impl.h b/src/internal/fork_impl.h
new file mode 100644
index 00000000..0e116aae
--- /dev/null
+++ b/src/internal/fork_impl.h
@@ -0,0 +1,18 @@
+#include <features.h>
+
+extern hidden volatile int *const __at_quick_exit_lockptr;
+extern hidden volatile int *const __atexit_lockptr;
+extern hidden volatile int *const __dlerror_lockptr;
+extern hidden volatile int *const __gettext_lockptr;
+extern hidden volatile int *const __random_lockptr;
+extern hidden volatile int *const __sem_open_lockptr;
+extern hidden volatile int *const __stdio_ofl_lockptr;
+extern hidden volatile int *const __syslog_lockptr;
+extern hidden volatile int *const __timezone_lockptr;
+
+extern hidden volatile int *const __bump_lockptr;
+
+extern hidden volatile int *const __vmlock_lockptr;
+
+hidden void __malloc_atfork(int);
+hidden void __ldso_atfork(int);
diff --git a/src/ldso/dlerror.c b/src/ldso/dlerror.c
index 3fcc7779..009beecb 100644
--- a/src/ldso/dlerror.c
+++ b/src/ldso/dlerror.c
@@ -4,6 +4,7 @@
 #include "pthread_impl.h"
 #include "dynlink.h"
 #include "lock.h"
+#include "fork_impl.h"
 
 char *dlerror()
 {
@@ -19,6 +20,7 @@ char *dlerror()
 
 static volatile int freebuf_queue_lock[1];
 static void **freebuf_queue;
+volatile int *const __dlerror_lockptr = freebuf_queue_lock;
 
 void __dl_thread_cleanup(void)
 {
diff --git a/src/locale/dcngettext.c b/src/locale/dcngettext.c
index 4c304393..805fe83b 100644
--- a/src/locale/dcngettext.c
+++ b/src/locale/dcngettext.c
@@ -10,6 +10,7 @@
 #include "atomic.h"
 #include "pleval.h"
 #include "lock.h"
+#include "fork_impl.h"
 
 struct binding {
 	struct binding *next;
@@ -34,9 +35,11 @@ static char *gettextdir(const char *domainname, size_t *dirlen)
 	return 0;
 }
 
+static volatile int lock[1];
+volatile int *const __gettext_lockptr = lock;
+
 char *bindtextdomain(const char *domainname, const char *dirname)
 {
-	static volatile int lock[1];
 	struct binding *p, *q;
 
 	if (!domainname) return 0;
diff --git a/src/malloc/lite_malloc.c b/src/malloc/lite_malloc.c
index f8931ba5..f6736ec4 100644
--- a/src/malloc/lite_malloc.c
+++ b/src/malloc/lite_malloc.c
@@ -6,6 +6,7 @@
 #include "libc.h"
 #include "lock.h"
 #include "syscall.h"
+#include "fork_impl.h"
 
 #define ALIGN 16
 
@@ -31,10 +32,12 @@ static int traverses_stack_p(uintptr_t old, uintptr_t new)
 	return 0;
 }
 
+static volatile int lock[1];
+volatile int *const __bump_lockptr = lock;
+
 static void *__simple_malloc(size_t n)
 {
 	static uintptr_t brk, cur, end;
-	static volatile int lock[1];
 	static unsigned mmap_step;
 	size_t align=1;
 	void *p;
diff --git a/src/malloc/mallocng/glue.h b/src/malloc/mallocng/glue.h
index 16acd1ea..980ce396 100644
--- a/src/malloc/mallocng/glue.h
+++ b/src/malloc/mallocng/glue.h
@@ -56,7 +56,8 @@ __attribute__((__visibility__("hidden")))
 extern int __malloc_lock[1];
 
 #define LOCK_OBJ_DEF \
-int __malloc_lock[1];
+int __malloc_lock[1]; \
+void __malloc_atfork(int who) { malloc_atfork(who); }
 
 static inline void rdlock()
 {
@@ -73,5 +74,16 @@ static inline void unlock()
 static inline void upgradelock()
 {
 }
+static inline void resetlock()
+{
+	__malloc_lock[0] = 0;
+}
+
+static inline void malloc_atfork(int who)
+{
+	if (who<0) rdlock();
+	else if (who>0) resetlock();
+	else unlock();
+}
 
 #endif
diff --git a/src/malloc/oldmalloc/malloc.c b/src/malloc/oldmalloc/malloc.c
index c0997ad8..8ac68a24 100644
--- a/src/malloc/oldmalloc/malloc.c
+++ b/src/malloc/oldmalloc/malloc.c
@@ -9,6 +9,7 @@
 #include "atomic.h"
 #include "pthread_impl.h"
 #include "malloc_impl.h"
+#include "fork_impl.h"
 
 #if defined(__GNUC__) && defined(__PIC__)
 #define inline inline __attribute__((always_inline))
@@ -527,3 +528,21 @@ void __malloc_donate(char *start, char *end)
 	c->csize = n->psize = C_INUSE | (end-start);
 	__bin_chunk(c);
 }
+
+void __malloc_atfork(int who)
+{
+	if (who<0) {
+		lock(mal.split_merge_lock);
+		for (int i=0; i<64; i++)
+			lock(mal.bins[i].lock);
+	} else if (!who) {
+		for (int i=0; i<64; i++)
+			unlock(mal.bins[i].lock);
+		unlock(mal.split_merge_lock);
+	} else {
+		for (int i=0; i<64; i++)
+			mal.bins[i].lock[0] = mal.bins[i].lock[1] = 0;
+		mal.split_merge_lock[1] = 0;
+		mal.split_merge_lock[0] = 0;
+	}
+}
diff --git a/src/misc/syslog.c b/src/misc/syslog.c
index 13d4b0a6..7dc0c1be 100644
--- a/src/misc/syslog.c
+++ b/src/misc/syslog.c
@@ -10,6 +10,7 @@
 #include <errno.h>
 #include <fcntl.h>
 #include "lock.h"
+#include "fork_impl.h"
 
 static volatile int lock[1];
 static char log_ident[32];
@@ -17,6 +18,7 @@ static int log_opt;
 static int log_facility = LOG_USER;
 static int log_mask = 0xff;
 static int log_fd = -1;
+volatile int *const __syslog_lockptr = lock;
 
 int setlogmask(int maskpri)
 {
diff --git a/src/prng/random.c b/src/prng/random.c
index 633a17f6..d3780fa7 100644
--- a/src/prng/random.c
+++ b/src/prng/random.c
@@ -1,6 +1,7 @@
 #include <stdlib.h>
 #include <stdint.h>
 #include "lock.h"
+#include "fork_impl.h"
 
 /*
 this code uses the same lagged fibonacci generator as the
@@ -23,6 +24,7 @@ static int i = 3;
 static int j = 0;
 static uint32_t *x = init+1;
 static volatile int lock[1];
+volatile int *const __random_lockptr = lock;
 
 static uint32_t lcg31(uint32_t x) {
 	return (1103515245*x + 12345) & 0x7fffffff;
diff --git a/src/process/fork.c b/src/process/fork.c
index 8d34a9c4..25808d85 100644
--- a/src/process/fork.c
+++ b/src/process/fork.c
@@ -1,15 +1,83 @@
 #include <unistd.h>
 #include <errno.h>
 #include "libc.h"
+#include "lock.h"
+#include "pthread_impl.h"
+#include "fork_impl.h"
+
+static volatile int *const dummy_lockptr = 0;
+
+weak_alias(dummy_lockptr, __at_quick_exit_lockptr);
+weak_alias(dummy_lockptr, __atexit_lockptr);
+weak_alias(dummy_lockptr, __dlerror_lockptr);
+weak_alias(dummy_lockptr, __gettext_lockptr);
+weak_alias(dummy_lockptr, __random_lockptr);
+weak_alias(dummy_lockptr, __sem_open_lockptr);
+weak_alias(dummy_lockptr, __stdio_ofl_lockptr);
+weak_alias(dummy_lockptr, __syslog_lockptr);
+weak_alias(dummy_lockptr, __timezone_lockptr);
+weak_alias(dummy_lockptr, __bump_lockptr);
+
+weak_alias(dummy_lockptr, __vmlock_lockptr);
+
+static volatile int *const *const atfork_locks[] = {
+	&__at_quick_exit_lockptr,
+	&__atexit_lockptr,
+	&__dlerror_lockptr,
+	&__gettext_lockptr,
+	&__random_lockptr,
+	&__sem_open_lockptr,
+	&__stdio_ofl_lockptr,
+	&__syslog_lockptr,
+	&__timezone_lockptr,
+	&__bump_lockptr,
+};
 
 static void dummy(int x) { }
 weak_alias(dummy, __fork_handler);
+weak_alias(dummy, __malloc_atfork);
+weak_alias(dummy, __ldso_atfork);
+
+static void dummy_0(void) { }
+weak_alias(dummy_0, __tl_lock);
+weak_alias(dummy_0, __tl_unlock);
 
 pid_t fork(void)
 {
+	sigset_t set;
 	__fork_handler(-1);
+	__block_app_sigs(&set);
+	int need_locks = libc.need_locks > 0;
+	if (need_locks) {
+		__ldso_atfork(-1);
+		__inhibit_ptc();
+		for (int i=0; i<sizeof atfork_locks/sizeof *atfork_locks; i++)
+			if (*atfork_locks[i]) LOCK(*atfork_locks[i]);
+		__malloc_atfork(-1);
+		__tl_lock();
+	}
+	pthread_t self=__pthread_self(), next=self->next;
 	pid_t ret = _Fork();
 	int errno_save = errno;
+	if (need_locks) {
+		if (!ret) {
+			for (pthread_t td=next; td!=self; td=td->next)
+				td->tid = -1;
+			if (__vmlock_lockptr) {
+				__vmlock_lockptr[0] = 0;
+				__vmlock_lockptr[1] = 0;
+			}
+		}
+		__tl_unlock();
+		__malloc_atfork(!ret);
+		for (int i=0; i<sizeof atfork_locks/sizeof *atfork_locks; i++)
+			if (*atfork_locks[i])
+				if (ret) UNLOCK(*atfork_locks[i]);
+				else **atfork_locks[i] = 0;
+		__release_ptc();
+		__ldso_atfork(!ret);
+	}
+	__restore_sigs(&set);
 	__fork_handler(!ret);
 	if (ret<0) errno = errno_save;
 	return ret;
diff --git a/src/stdio/ofl.c b/src/stdio/ofl.c
index f2d3215a..aad3d171 100644
--- a/src/stdio/ofl.c
+++ b/src/stdio/ofl.c
@@ -1,8 +1,10 @@
 #include "stdio_impl.h"
 #include "lock.h"
+#include "fork_impl.h"
 
 static FILE *ofl_head;
 static volatile int ofl_lock[1];
+volatile int *const __stdio_ofl_lockptr = ofl_lock;
 
 FILE **__ofl_lock()
 {
diff --git a/src/thread/sem_open.c b/src/thread/sem_open.c
index de8555c5..f198056e 100644
--- a/src/thread/sem_open.c
+++ b/src/thread/sem_open.c
@@ -12,6 +12,7 @@
 #include <stdlib.h>
 #include <pthread.h>
 #include "lock.h"
+#include "fork_impl.h"
 
 static struct {
 	ino_t ino;
@@ -19,6 +20,7 @@ static struct {
 	int refcnt;
 } *semtab;
 static volatile int lock[1];
+volatile int *const __sem_open_lockptr = lock;
 
 #define FLAGS (O_RDWR|O_NOFOLLOW|O_CLOEXEC|O_NONBLOCK)
 
diff --git a/src/thread/vmlock.c b/src/thread/vmlock.c
index 75f3cb76..fa0a8e3c 100644
--- a/src/thread/vmlock.c
+++ b/src/thread/vmlock.c
@@ -1,6 +1,8 @@
 #include "pthread_impl.h"
+#include "fork_impl.h"
 
 static volatile int vmlock[2];
+volatile int *const __vmlock_lockptr = vmlock;
 
 void __vm_wait()
 {
diff --git a/src/time/__tz.c b/src/time/__tz.c
index 49a7371e..72c0d58b 100644
--- a/src/time/__tz.c
+++ b/src/time/__tz.c
@@ -6,6 +6,7 @@
 #include <sys/mman.h>
 #include "libc.h"
 #include "lock.h"
+#include "fork_impl.h"
 
 long  __timezone = 0;
 int   __daylight = 0;
@@ -30,6 +31,7 @@ static char *old_tz = old_tz_buf;
 static size_t old_tz_size = sizeof old_tz_buf;
 
 static volatile int lock[1];
+volatile int *const __timezone_lockptr = lock;
 
 static int getint(const char **p)
 {