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Eliminate cyclic locks in runtime

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This change introduces a new deadlock detector for Cosmo's POSIX threads
implementation. Error check mutexes will now track a DAG of nested locks
and report EDEADLK when a deadlock is theoretically possible. These will
occur rarely, but it's important for production hardening your code. You
don't even need to change your mutexes to use the POSIX error check mode
because `cosmocc -mdbg` will enable error checking on mutexes by default
globally. When cycles are found, an error message showing your demangled
symbols describing the strongly connected component are printed and then
the SIGTRAP is raised, which means you'll also get a backtrace if you're
using ShowCrashReports() too. This new error checker is so low-level and
so pure that it's able to verify the relationships of every libc runtime
lock, including those locks upon which the mutex implementation depends.
This commit is contained in:
Justine Tunney 2024-12-16 20:51:27 -08:00
parent 26c051c297
commit af7bd80430
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GPG key ID: BE714B4575D6E328
141 changed files with 2094 additions and 1601 deletions
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10
libc/thread/pthread_cond_timedwait.c
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@ -43,7 +43,7 @@ struct PthreadWait {
static bool can_use_nsync(uint64_t muword) {
return !IsXnuSilicon() && //
MUTEX_TYPE(muword) == PTHREAD_MUTEX_NORMAL &&
MUTEX_TYPE(muword) != PTHREAD_MUTEX_RECURSIVE &&
MUTEX_PSHARED(muword) == PTHREAD_PROCESS_PRIVATE;
}
@ -124,9 +124,9 @@ errno_t pthread_cond_timedwait(pthread_cond_t *cond, pthread_mutex_t *mutex,
uint64_t muword = atomic_load_explicit(&mutex->_word, memory_order_relaxed);
// check that mutex is held by caller
if (MUTEX_TYPE(muword) == PTHREAD_MUTEX_ERRORCHECK &&
MUTEX_OWNER(muword) != gettid())
return EPERM;
if (IsModeDbg() || MUTEX_TYPE(muword) == PTHREAD_MUTEX_ERRORCHECK)
if (__deadlock_tracked(mutex) == 0)
return EPERM;
// if the cond is process shared then the mutex needs to be too
if ((cond->_pshared == PTHREAD_PROCESS_SHARED) ^
@ -154,7 +154,7 @@ errno_t pthread_cond_timedwait(pthread_cond_t *cond, pthread_mutex_t *mutex,
// if using Mike Burrows' code isn't possible, use a naive impl
if (!cond->_footek) {
err = nsync_cv_wait_with_deadline(
(nsync_cv *)cond, (nsync_mu *)mutex, cond->_clock,
(nsync_cv *)cond->_nsync, (nsync_mu *)mutex->_nsync, cond->_clock,
abstime ? *abstime : nsync_time_no_deadline, 0);
} else {
err = pthread_cond_timedwait_impl(cond, mutex, abstime);