diff options
Diffstat (limited to 'toolchain/musl/patches/500-0004-restore-lock-skipping-for-processes-that-return-to-s.patch')
| -rw-r--r-- | toolchain/musl/patches/500-0004-restore-lock-skipping-for-processes-that-return-to-s.patch | 90 |
1 files changed, 90 insertions, 0 deletions
diff --git a/toolchain/musl/patches/500-0004-restore-lock-skipping-for-processes-that-return-to-s.patch b/toolchain/musl/patches/500-0004-restore-lock-skipping-for-processes-that-return-to-s.patch new file mode 100644 index 0000000000..83a6d0247a --- /dev/null +++ b/toolchain/musl/patches/500-0004-restore-lock-skipping-for-processes-that-return-to-s.patch @@ -0,0 +1,90 @@ +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(-) + +--- 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; +--- 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) +--- 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) { +--- a/src/thread/pthread_create.c ++++ b/src/thread/pthread_create.c +@@ -118,8 +118,8 @@ _Noreturn void __pthread_exit(void *resu + * 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 + ~(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 + 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); |