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Fix fork waiter leak in nsync

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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 2024-12-31 00:55:15 -08:00
parent fd7da586b5
commit 98c5847727
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GPG key ID: BE714B4575D6E328
35 changed files with 299 additions and 173 deletions
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38
libc/thread/pthread_create.c
View file

@ -57,6 +57,7 @@
#include "libc/thread/posixthread.internal.h"
#include "libc/thread/thread.h"
#include "libc/thread/tls.h"
#include "third_party/nsync/wait_s.internal.h"
__static_yoink("nsync_mu_lock");
__static_yoink("nsync_mu_unlock");
@ -81,6 +82,10 @@ void _pthread_free(struct PosixThread *pt) {
cosmo_stack_free(pt->pt_attr.__stackaddr, pt->pt_attr.__stacksize,
pt->pt_attr.__guardsize);
// reclaim thread's cached nsync waiter object
if (pt->tib->tib_nsync)
nsync_waiter_destroy_(pt->tib->tib_nsync);
// free any additional upstream system resources
// our fork implementation wipes this handle in child automatically
uint64_t syshand =
@ -102,7 +107,7 @@ void _pthread_free(struct PosixThread *pt) {
3);
}
void _pthread_decimate(void) {
void _pthread_decimate(enum PosixThreadStatus threshold) {
struct PosixThread *pt;
struct Dll *e, *e2, *list = 0;
enum PosixThreadStatus status;
@ -117,11 +122,18 @@ void _pthread_decimate(void) {
pt = POSIXTHREAD_CONTAINER(e);
if (atomic_load_explicit(&pt->pt_refs, memory_order_acquire) > 0)
continue; // pthread_kill() has a lease on this thread
if (atomic_load_explicit(&pt->tib->tib_ctid, memory_order_acquire))
continue; // thread is still using stack so leave alone
status = atomic_load_explicit(&pt->pt_status, memory_order_acquire);
if (status != kPosixThreadZombie)
break; // zombies only exist at the end of the linked list
if (atomic_load_explicit(&pt->tib->tib_tid, memory_order_acquire))
continue; // undead thread that should stop existing soon
if (status < threshold) {
if (threshold == kPosixThreadZombie)
break; // zombies only exist at the end of the linked list
continue;
}
if (status == kPosixThreadTerminated)
if (!(pt->pt_flags & PT_STATIC))
STRACE("warning: you forgot to join or detach thread id %d",
atomic_load_explicit(&pt->tib->tib_ptid, memory_order_acquire));
dll_remove(&_pthread_list, e);
dll_make_first(&list, e);
}
@ -139,7 +151,7 @@ void _pthread_decimate(void) {
}
}
static int PosixThread(void *arg, int tid) {
dontinstrument static int PosixThread(void *arg, int tid) {
struct PosixThread *pt = arg;
// setup scheduling
@ -285,12 +297,12 @@ static errno_t pthread_create_impl(pthread_t *thread,
_pthread_ref(pt);
// launch PosixThread(pt) in new thread
if ((rc = clone(PosixThread, pt->pt_attr.__stackaddr, pt->pt_attr.__stacksize,
CLONE_VM | CLONE_THREAD | CLONE_FS | CLONE_FILES |
CLONE_SIGHAND | CLONE_SYSVSEM | CLONE_SETTLS |
CLONE_PARENT_SETTID | CLONE_CHILD_SETTID |
CLONE_CHILD_CLEARTID,
pt, &pt->ptid, __adj_tls(pt->tib), &pt->tib->tib_tid))) {
if ((rc = clone(
PosixThread, pt->pt_attr.__stackaddr, pt->pt_attr.__stacksize,
CLONE_VM | CLONE_THREAD | CLONE_FS | CLONE_FILES | CLONE_SIGHAND |
CLONE_SYSVSEM | CLONE_SETTLS | CLONE_PARENT_SETTID |
CLONE_CHILD_SETTID | CLONE_CHILD_CLEARTID,
pt, &pt->tib->tib_ptid, __adj_tls(pt->tib), &pt->tib->tib_ctid))) {
_pthread_lock();
dll_remove(&_pthread_list, &pt->list);
_pthread_unlock();
@ -363,7 +375,7 @@ static const char *DescribeHandle(char buf[12], errno_t err, pthread_t *th) {
errno_t pthread_create(pthread_t *thread, const pthread_attr_t *attr,
void *(*start_routine)(void *), void *arg) {
errno_t err;
_pthread_decimate();
_pthread_decimate(kPosixThreadZombie);
BLOCK_SIGNALS;
err = pthread_create_impl(thread, attr, start_routine, arg, _SigMask);
ALLOW_SIGNALS;