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https://github.com/jart/cosmopolitan.git
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Fix fork waiter leak in nsync
This change fixes a bug where nsync waiter objects would leak. It'd mean that long-running programs like runitd would run out of file descriptors on NetBSD where waiter objects have ksem file descriptors. On other OSes this bug is mostly harmless since the worst that can happen with a futex is to leak a little bit of ram. The bug was caused because tib_nsync was sneaking back in after the finalization code had cleared it. This change refactors the thread exiting code to handle nsync teardown appropriately and in making this change I found another issue, which is that user code which is buggy, and tries to exit without joining joinable threads which haven't been detached, would result in a deadlock. That doesn't sound so bad, except the main thread is a joinable thread. So this deadlock would be triggered in ways that put libc at fault. So we now auto-join threads and libc will log a warning to --strace when that happens for any thread
This commit is contained in:
Justine Tunney
parent
fd7da586b5
commit
98c5847727
35 changed files with 299 additions and 173 deletions
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@ -120,11 +120,13 @@ WinThreadEntry(int rdi, // rcx
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int rc;
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if (wt->tls)
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__set_tls_win32(wt->tls);
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*wt->ctid = __imp_GetCurrentThreadId();
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int tid = __imp_GetCurrentThreadId();
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atomic_init(wt->ptid, tid);
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atomic_init(wt->ctid, tid);
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rc = __stack_call(wt->arg, wt->tid, 0, 0, wt->func, wt->sp);
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// we can now clear ctid directly since we're no longer using our own
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// stack memory, which can now be safely free'd by the parent thread.
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*wt->ztid = 0;
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atomic_store_explicit(wt->ztid, 0, memory_order_release);
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__imp_WakeByAddressAll(wt->ztid);
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// since we didn't indirect this function through NT2SYSV() it's not
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// safe to simply return, and as such, we need ExitThread().
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@ -146,6 +148,7 @@ static textwindows errno_t CloneWindows(int (*func)(void *, int), char *stk,
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sp &= -alignof(struct CloneArgs);
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wt = (struct CloneArgs *)sp;
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wt->ctid = flags & CLONE_CHILD_SETTID ? ctid : &wt->tid;
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wt->ptid = flags & CLONE_PARENT_SETTID ? ptid : &wt->tid;
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wt->ztid = flags & CLONE_CHILD_CLEARTID ? ctid : &wt->tid;
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wt->func = func;
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wt->arg = arg;
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@ -154,7 +157,7 @@ static textwindows errno_t CloneWindows(int (*func)(void *, int), char *stk,
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if ((h = CreateThread(&kNtIsInheritable, 65536, (void *)WinThreadEntry, wt,
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kNtStackSizeParamIsAReservation, &utid))) {
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if (flags & CLONE_PARENT_SETTID)
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*ptid = utid;
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atomic_init(ptid, utid);
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if (flags & CLONE_SETTLS) {
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struct CosmoTib *tib = tls;
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atomic_store_explicit(&tib->tib_syshand, h, memory_order_release);
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@ -192,8 +195,8 @@ XnuThreadMain(void *pthread, // rdi
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int ax;
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wt->tid = tid;
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*wt->ctid = tid;
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*wt->ptid = tid;
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atomic_init(wt->ctid, tid);
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atomic_init(wt->ptid, tid);
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if (wt->tls) {
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// XNU uses the same 0x30 offset as the WIN32 TIB x64. They told the
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@ -250,8 +253,8 @@ static errno_t CloneXnu(int (*fn)(void *), char *stk, size_t stksz, int flags,
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wt = (struct CloneArgs *)sp;
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// pass parameters to new thread via xnu
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wt->ptid = flags & CLONE_PARENT_SETTID ? ptid : &wt->tid;
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wt->ctid = flags & CLONE_CHILD_SETTID ? ctid : &wt->tid;
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wt->ptid = flags & CLONE_PARENT_SETTID ? ptid : &wt->tid;
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wt->ztid = flags & CLONE_CHILD_CLEARTID ? ctid : &wt->tid;
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wt->tls = flags & CLONE_SETTLS ? tls : 0;
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return sys_clone_xnu(fn, arg, wt, 0, PTHREAD_START_CUSTOM_XNU);
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@ -264,7 +267,8 @@ static errno_t CloneXnu(int (*fn)(void *), char *stk, size_t stksz, int flags,
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// 1. __asan_handle_no_return wipes stack [todo?]
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relegated static wontreturn void OpenbsdThreadMain(void *p) {
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struct CloneArgs *wt = p;
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*wt->ctid = wt->tid;
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atomic_init(wt->ptid, wt->tid);
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atomic_init(wt->ctid, wt->tid);
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wt->func(wt->arg, wt->tid);
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asm volatile("mov\t%2,%%rsp\n\t" // so syscall can validate stack exists
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"movl\t$0,(%%rdi)\n\t" // *wt->ztid = 0 (old stack now free'd)
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@ -295,6 +299,7 @@ relegated errno_t CloneOpenbsd(int (*func)(void *, int), char *stk,
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wt = (struct CloneArgs *)sp;
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sp = AlignStack(sp, stk, stksz, 16);
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wt->ctid = flags & CLONE_CHILD_SETTID ? ctid : &wt->tid;
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wt->ptid = flags & CLONE_PARENT_SETTID ? ptid : &wt->tid;
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wt->ztid = flags & CLONE_CHILD_CLEARTID ? ctid : &wt->tid;
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wt->arg = arg;
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wt->func = func;
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@ -303,7 +308,7 @@ relegated errno_t CloneOpenbsd(int (*func)(void *, int), char *stk,
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tf->tf_tid = &wt->tid;
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if ((rc = __tfork_thread(tf, sizeof(*tf), OpenbsdThreadMain, wt)) >= 0) {
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if (flags & CLONE_PARENT_SETTID)
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*ptid = rc;
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atomic_init(ptid, rc);
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return 0;
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} else {
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return -rc;
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@ -316,13 +321,16 @@ relegated errno_t CloneOpenbsd(int (*func)(void *, int), char *stk,
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static wontreturn void NetbsdThreadMain(void *arg, // rdi
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int (*func)(void *, int), // rsi
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int flags, // rdx
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atomic_int *ctid) { // rcx
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atomic_int *ctid, // rcx
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atomic_int *ptid) { // r8
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int ax, dx;
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static atomic_int clobber;
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atomic_int *ztid = &clobber;
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ax = sys_gettid();
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if (flags & CLONE_CHILD_SETTID)
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atomic_store_explicit(ctid, ax, memory_order_release);
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atomic_init(ctid, ax);
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if (flags & CLONE_PARENT_SETTID)
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atomic_init(ptid, ax);
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if (flags & CLONE_CHILD_CLEARTID)
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ztid = ctid;
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func(arg, ax);
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@ -381,6 +389,7 @@ static int CloneNetbsd(int (*func)(void *, int), char *stk, size_t stksz,
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ctx->uc_mcontext.rsi = (intptr_t)func;
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ctx->uc_mcontext.rdx = flags;
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ctx->uc_mcontext.rcx = (intptr_t)ctid;
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ctx->uc_mcontext.r8 = (intptr_t)ptid;
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ctx->uc_flags |= _UC_STACK;
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ctx->uc_stack.ss_sp = stk;
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ctx->uc_stack.ss_size = stksz;
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@ -399,7 +408,7 @@ static int CloneNetbsd(int (*func)(void *, int), char *stk, size_t stksz,
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if (!failed) {
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unassert(tid);
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if (flags & CLONE_PARENT_SETTID)
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*ptid = tid;
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atomic_init(ptid, tid);
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return 0;
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} else {
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return ax;
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@ -418,7 +427,8 @@ static wontreturn void FreebsdThreadMain(void *p) {
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#elif defined(__x86_64__)
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sys_set_tls(AMD64_SET_GSBASE, wt->tls);
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#endif
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*wt->ctid = wt->tid;
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atomic_init(wt->ctid, wt->tid);
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atomic_init(wt->ptid, wt->tid);
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wt->func(wt->arg, wt->tid);
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// we no longer use the stack after this point
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// void thr_exit(%rdi = long *state);
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@ -465,6 +475,7 @@ static errno_t CloneFreebsd(int (*func)(void *, int), char *stk, size_t stksz,
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wt = (struct CloneArgs *)sp;
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sp = AlignStack(sp, stk, stksz, 16);
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wt->ctid = flags & CLONE_CHILD_SETTID ? ctid : &wt->tid;
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wt->ptid = flags & CLONE_PARENT_SETTID ? ptid : &wt->tid;
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wt->ztid = flags & CLONE_CHILD_CLEARTID ? ctid : &wt->tid;
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wt->tls = tls;
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wt->func = func;
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@ -499,7 +510,7 @@ static errno_t CloneFreebsd(int (*func)(void *, int), char *stk, size_t stksz,
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#error "unsupported architecture"
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#endif
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if (flags & CLONE_PARENT_SETTID)
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*ptid = tid;
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atomic_init(ptid, tid);
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return 0;
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}
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@ -511,9 +522,10 @@ static errno_t CloneFreebsd(int (*func)(void *, int), char *stk, size_t stksz,
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static void *SiliconThreadMain(void *arg) {
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struct CloneArgs *wt = arg;
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asm volatile("mov\tx28,%0" : /* no outputs */ : "r"(wt->tls));
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*wt->ctid = wt->this;
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atomic_init(wt->ctid, wt->this);
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atomic_init(wt->ptid, wt->this);
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__stack_call(wt->arg, wt->this, 0, 0, wt->func, wt->sp);
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*wt->ztid = 0;
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atomic_store_explicit(wt->ztid, 0, memory_order_release);
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ulock_wake(UL_COMPARE_AND_WAIT | ULF_WAKE_ALL, wt->ztid, 0);
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return 0;
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}
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@ -537,6 +549,7 @@ static errno_t CloneSilicon(int (*fn)(void *, int), char *stk, size_t stksz,
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tid = atomic_fetch_add_explicit(&tids, 1, memory_order_acq_rel);
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wt->this = tid = (tid % kMaxThreadIds) + kMinThreadId;
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wt->ctid = flags & CLONE_CHILD_SETTID ? ctid : &wt->tid;
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wt->ptid = flags & CLONE_PARENT_SETTID ? ptid : &wt->tid;
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wt->ztid = flags & CLONE_CHILD_CLEARTID ? ctid : &wt->tid;
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wt->tls = flags & CLONE_SETTLS ? tls : 0;
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wt->func = fn;
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@ -552,7 +565,7 @@ static errno_t CloneSilicon(int (*fn)(void *, int), char *stk, size_t stksz,
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unassert(!__syslib->__pthread_attr_setstacksize(attr, babystack));
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if (!(res = __syslib->__pthread_create(&th, attr, SiliconThreadMain, wt))) {
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if (flags & CLONE_PARENT_SETTID)
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*ptid = tid;
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atomic_init(ptid, tid);
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if (flags & CLONE_SETTLS) {
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struct CosmoTib *tib = tls;
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atomic_store_explicit(&tib[-1].tib_syshand, th, memory_order_release);
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@ -637,7 +650,7 @@ static int CloneLinux(int (*func)(void *arg, int rc), char *stk, size_t stksz,
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* If you use clone() you're on your own. Example:
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*
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* int worker(void *arg) { return 0; }
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* struct CosmoTib tib = {.tib_self = &tib, .tib_tid = -1};
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* struct CosmoTib tib = {.tib_self = &tib, .tib_ctid = -1};
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* atomic_int tid;
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* char *stk = NewCosmoStack();
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* clone(worker, stk, GetStackSize() - 16,
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@ -647,9 +660,9 @@ static int CloneLinux(int (*func)(void *arg, int rc), char *stk, size_t stksz,
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* arg, &tid, &tib, &tib.tib_tid);
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* while (atomic_load(&tid) == 0) sched_yield();
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* // thread is known
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* while (atomic_load(&tib.tib_tid) < 0) sched_yield();
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* while (atomic_load(&tib.tib_ctid) < 0) sched_yield();
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* // thread is running
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* while (atomic_load(&tib.tib_tid) > 0) sched_yield();
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* while (atomic_load(&tib.tib_ctid) > 0) sched_yield();
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* // thread has terminated
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* FreeCosmoStack(stk);
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*
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