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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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141 changed files with 2094 additions and 1601 deletions
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41
libc/intrin/pthread_mutex_consistent.c Normal file
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/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│ vi: set et ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi │
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2024 Justine Alexandra Roberts Tunney │
│ │
│ Permission to use, copy, modify, and/or distribute this software for │
│ any purpose with or without fee is hereby granted, provided that the │
│ above copyright notice and this permission notice appear in all copies. │
│ │
│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
│ PERFORMANCE OF THIS SOFTWARE. │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/cosmo.h"
#include "libc/dce.h"
#include "libc/intrin/atomic.h"
#include "libc/thread/lock.h"
#include "libc/thread/thread.h"
/**
* Recovers mutex whose owner died.
*
* @return 0 on success, or errno on error
*/
int pthread_mutex_consistent(pthread_mutex_t *mutex) {
// The POSIX concept of robust mutexes is a bit cray. So let's change
// things up a bit. Rather than implementing all those goofy behaviors
// we shall simply use this function to weasel around the ownership
// check in pthread_mutex_unlock().
uint64_t word = atomic_load_explicit(&mutex->_word, memory_order_relaxed);
if (IsModeDbg() || MUTEX_TYPE(word) == PTHREAD_MUTEX_ERRORCHECK)
__deadlock_track(mutex, 0);
return 0;
}