diff options
Diffstat (limited to 'system/musl/threads_minus_1.patch')
| -rw-r--r-- | system/musl/threads_minus_1.patch | 267 |
1 files changed, 0 insertions, 267 deletions
diff --git a/system/musl/threads_minus_1.patch b/system/musl/threads_minus_1.patch deleted file mode 100644 index 05307d97c..000000000 --- a/system/musl/threads_minus_1.patch +++ /dev/null @@ -1,267 +0,0 @@ -https://www.openwall.com/lists/musl/2020/05/22/10 - -From 4d5aa20a94a2d3fae3e69289dc23ecafbd0c16c4 Mon Sep 17 00:00:00 2001 -From: Rich Felker <dalias@aerifal.cx> -Date: Fri, 22 May 2020 17:35:14 -0400 -Subject: [PATCH 1/4] reorder thread list unlink in pthread_exit after all - locks - -since the backend for LOCK() skips locking if single-threaded, it's -unsafe to make the process appear single-threaded before the last use -of lock. - -this fixes potential unsynchronized access to a linked list via -__dl_thread_cleanup. ---- - src/thread/pthread_create.c | 19 +++++++++++-------- - 1 file changed, 11 insertions(+), 8 deletions(-) - -diff --git a/src/thread/pthread_create.c b/src/thread/pthread_create.c -index 5f491092..6a3b0c21 100644 ---- a/src/thread/pthread_create.c -+++ b/src/thread/pthread_create.c -@@ -90,14 +90,7 @@ _Noreturn void __pthread_exit(void *result) - exit(0); - } - -- /* At this point we are committed to thread termination. Unlink -- * the thread from the list. This change will not be visible -- * until the lock is released, which only happens after SYS_exit -- * has been called, via the exit futex address pointing at the lock. */ -- libc.threads_minus_1--; -- self->next->prev = self->prev; -- self->prev->next = self->next; -- self->prev = self->next = self; -+ /* At this point we are committed to thread termination. */ - - /* Process robust list in userspace to handle non-pshared mutexes - * and the detached thread case where the robust list head will -@@ -121,6 +114,16 @@ _Noreturn void __pthread_exit(void *result) - __do_orphaned_stdio_locks(); - __dl_thread_cleanup(); - -+ /* Last, unlink thread from the list. This change will not be visible -+ * until the lock is released, which only happens after SYS_exit -+ * has been called, via the exit futex address pointing at the lock. -+ * This needs to happen after any possible calls to LOCK() that might -+ * skip locking if libc.threads_minus_1 is zero. */ -+ libc.threads_minus_1--; -+ self->next->prev = self->prev; -+ self->prev->next = self->next; -+ self->prev = self->next = self; -+ - /* This atomic potentially competes with a concurrent pthread_detach - * call; the loser is responsible for freeing thread resources. */ - int state = a_cas(&self->detach_state, DT_JOINABLE, DT_EXITING); --- -2.21.0 - -From e01b5939b38aea5ecbe41670643199825874b26c Mon Sep 17 00:00:00 2001 -From: Rich Felker <dalias@aerifal.cx> -Date: Thu, 21 May 2020 23:32:45 -0400 -Subject: [PATCH 2/4] don't use libc.threads_minus_1 as relaxed atomic for - skipping locks - -after all but the last thread exits, the next thread to observe -libc.threads_minus_1==0 and conclude that it can skip locking fails to -synchronize with any changes to memory that were made by the -last-exiting thread. this can produce data races. - -on some archs, at least x86, memory synchronization is unlikely to be -a problem; however, with the inline locks in malloc, skipping the lock -also eliminated the compiler barrier, and caused code that needed to -re-check chunk in-use bits after obtaining the lock to reuse a stale -value, possibly from before the process became single-threaded. this -in turn produced corruption of the heap state. - -some uses of libc.threads_minus_1 remain, especially for allocation of -new TLS in the dynamic linker; otherwise, it could be removed -entirely. it's made non-volatile to reflect that the remaining -accesses are only made under lock on the thread list. - -instead of libc.threads_minus_1, libc.threaded is now used for -skipping locks. the difference is that libc.threaded is permanently -true once an additional thread has been created. this will produce -some performance regression in processes that are mostly -single-threaded but occasionally creating threads. in the future it -may be possible to bring back the full lock-skipping, but more care -needs to be taken to produce a safe design. ---- - src/internal/libc.h | 2 +- - src/malloc/malloc.c | 2 +- - src/thread/__lock.c | 2 +- - 3 files changed, 3 insertions(+), 3 deletions(-) - -diff --git a/src/internal/libc.h b/src/internal/libc.h -index ac97dc7e..c0614852 100644 ---- a/src/internal/libc.h -+++ b/src/internal/libc.h -@@ -21,7 +21,7 @@ struct __libc { - int can_do_threads; - int threaded; - int secure; -- volatile int threads_minus_1; -+ int threads_minus_1; - size_t *auxv; - struct tls_module *tls_head; - size_t tls_size, tls_align, tls_cnt; -diff --git a/src/malloc/malloc.c b/src/malloc/malloc.c -index 96982596..2553a62e 100644 ---- a/src/malloc/malloc.c -+++ b/src/malloc/malloc.c -@@ -26,7 +26,7 @@ int __malloc_replaced; - - static inline void lock(volatile int *lk) - { -- if (libc.threads_minus_1) -+ if (libc.threaded) - while(a_swap(lk, 1)) __wait(lk, lk+1, 1, 1); - } - -diff --git a/src/thread/__lock.c b/src/thread/__lock.c -index 45557c88..5b9b144e 100644 ---- a/src/thread/__lock.c -+++ b/src/thread/__lock.c -@@ -18,7 +18,7 @@ - - void __lock(volatile int *l) - { -- if (!libc.threads_minus_1) return; -+ if (!libc.threaded) return; - /* fast path: INT_MIN for the lock, +1 for the congestion */ - int current = a_cas(l, 0, INT_MIN + 1); - if (!current) return; --- -2.21.0 - -From f12888e9eb9eed60cc266b899dcafecb4752964a Mon Sep 17 00:00:00 2001 -From: Rich Felker <dalias@aerifal.cx> -Date: Fri, 22 May 2020 17:25:38 -0400 -Subject: [PATCH 3/4] cut down size of some libc struct members - -these are all flags that can be single-byte values. ---- - src/internal/libc.h | 6 +++--- - 1 file changed, 3 insertions(+), 3 deletions(-) - -diff --git a/src/internal/libc.h b/src/internal/libc.h -index c0614852..d47f58e0 100644 ---- a/src/internal/libc.h -+++ b/src/internal/libc.h -@@ -18,9 +18,9 @@ struct tls_module { - }; - - struct __libc { -- int can_do_threads; -- int threaded; -- int secure; -+ char can_do_threads; -+ char threaded; -+ char secure; - int threads_minus_1; - size_t *auxv; - struct tls_module *tls_head; --- -2.21.0 - -From 8d81ba8c0bc6fe31136cb15c9c82ef4c24965040 Mon Sep 17 00:00:00 2001 -From: Rich Felker <dalias@aerifal.cx> -Date: Fri, 22 May 2020 17:45:47 -0400 -Subject: [PATCH 4/4] restore lock-skipping for processes that return to - single-threaded state - -the design used here relies on the barrier provided by the first lock -operation after the process returns to single-threaded state to -synchronize with actions by the last thread that exited. by storing -the intent to change modes in the same object used to detect whether -locking is needed, it's possible to avoid an extra (possibly costly) -memory load after the lock is taken. ---- - src/internal/libc.h | 1 + - src/malloc/malloc.c | 5 ++++- - src/thread/__lock.c | 4 +++- - src/thread/pthread_create.c | 8 ++++---- - 4 files changed, 12 insertions(+), 6 deletions(-) - -diff --git a/src/internal/libc.h b/src/internal/libc.h -index d47f58e0..619bba86 100644 ---- a/src/internal/libc.h -+++ b/src/internal/libc.h -@@ -21,6 +21,7 @@ struct __libc { - char can_do_threads; - char threaded; - char secure; -+ volatile signed char need_locks; - int threads_minus_1; - size_t *auxv; - struct tls_module *tls_head; -diff --git a/src/malloc/malloc.c b/src/malloc/malloc.c -index 2553a62e..a803d4c9 100644 ---- a/src/malloc/malloc.c -+++ b/src/malloc/malloc.c -@@ -26,8 +26,11 @@ int __malloc_replaced; - - static inline void lock(volatile int *lk) - { -- if (libc.threaded) -+ int need_locks = libc.need_locks; -+ if (need_locks) { - while(a_swap(lk, 1)) __wait(lk, lk+1, 1, 1); -+ if (need_locks < 0) libc.need_locks = 0; -+ } - } - - static inline void unlock(volatile int *lk) -diff --git a/src/thread/__lock.c b/src/thread/__lock.c -index 5b9b144e..60eece49 100644 ---- a/src/thread/__lock.c -+++ b/src/thread/__lock.c -@@ -18,9 +18,11 @@ - - void __lock(volatile int *l) - { -- if (!libc.threaded) return; -+ int need_locks = libc.need_locks; -+ if (!need_locks) return; - /* fast path: INT_MIN for the lock, +1 for the congestion */ - int current = a_cas(l, 0, INT_MIN + 1); -+ if (need_locks < 0) libc.need_locks = 0; - if (!current) return; - /* A first spin loop, for medium congestion. */ - for (unsigned i = 0; i < 10; ++i) { -diff --git a/src/thread/pthread_create.c b/src/thread/pthread_create.c -index 6a3b0c21..6bdfb44f 100644 ---- a/src/thread/pthread_create.c -+++ b/src/thread/pthread_create.c -@@ -118,8 +118,8 @@ _Noreturn void __pthread_exit(void *result) - * until the lock is released, which only happens after SYS_exit - * has been called, via the exit futex address pointing at the lock. - * This needs to happen after any possible calls to LOCK() that might -- * skip locking if libc.threads_minus_1 is zero. */ -- libc.threads_minus_1--; -+ * skip locking if process appears single-threaded. */ -+ if (!--libc.threads_minus_1) libc.need_locks = -1; - self->next->prev = self->prev; - self->prev->next = self->next; - self->prev = self->next = self; -@@ -339,7 +339,7 @@ int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict att - ~(1UL<<((SIGCANCEL-1)%(8*sizeof(long)))); - - __tl_lock(); -- libc.threads_minus_1++; -+ if (!libc.threads_minus_1++) libc.need_locks = 1; - ret = __clone((c11 ? start_c11 : start), stack, flags, args, &new->tid, TP_ADJ(new), &__thread_list_lock); - - /* All clone failures translate to EAGAIN. If explicit scheduling -@@ -363,7 +363,7 @@ int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict att - new->next->prev = new; - new->prev->next = new; - } else { -- libc.threads_minus_1--; -+ if (!--libc.threads_minus_1) libc.need_locks = 0; - } - __tl_unlock(); - __restore_sigs(&set); --- -2.21.0 - |