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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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68
libc/intrin/maps.c
View file

@ -19,14 +19,15 @@
#include "libc/intrin/maps.h"
#include "ape/sections.internal.h"
#include "libc/calls/state.internal.h"
#include "libc/cosmo.h"
#include "libc/dce.h"
#include "libc/intrin/describebacktrace.h"
#include "libc/intrin/dll.h"
#include "libc/intrin/kprintf.h"
#include "libc/intrin/maps.h"
#include "libc/nexgen32e/rdtsc.h"
#include "libc/runtime/runtime.h"
#include "libc/runtime/stack.h"
#include "libc/sysv/consts/auxv.h"
#include "libc/sysv/consts/prot.h"
#include "libc/thread/lock.h"
@ -34,6 +35,12 @@
__static_yoink("_init_maps");
#endif
#define ABI privileged optimizespeed
// take great care if you enable this
// especially if you're using --ftrace too
#define DEBUG_MAPS_LOCK 0
struct Maps __maps;
void __maps_add(struct Map *map) {
@ -65,6 +72,10 @@ void __maps_stack(char *stackaddr, int pagesz, int guardsize, size_t stacksize,
void __maps_init(void) {
int pagesz = __pagesize;
// initialize lemur64 rng
__maps.rand = 2131259787901769494;
__maps.rand ^= rdtsc();
// record _start() stack mapping
if (!IsWindows()) {
struct AddrSize stack;
@ -88,7 +99,16 @@ void __maps_init(void) {
__maps_adder(&text, pagesz);
}
privileged bool __maps_lock(void) {
#if DEBUG_MAPS_LOCK
privileged static void __maps_panic(const char *msg) {
// it's only safe to pass a format string. if we use directives such
// as %s, %t etc. then kprintf() will recursively call __maps_lock()
kprintf(msg);
DebugBreak();
}
#endif
ABI bool __maps_lock(void) {
int me;
uint64_t word, lock;
struct CosmoTib *tib;
@ -101,24 +121,35 @@ privileged bool __maps_lock(void) {
me = atomic_load_explicit(&tib->tib_tid, memory_order_acquire);
if (me <= 0)
return false;
word = atomic_load_explicit(&__maps.lock, memory_order_relaxed);
word = atomic_load_explicit(&__maps.lock.word, memory_order_relaxed);
for (;;) {
if (MUTEX_OWNER(word) == me) {
if (atomic_compare_exchange_weak_explicit(
&__maps.lock, &word, MUTEX_INC_DEPTH(word), memory_order_relaxed,
memory_order_relaxed))
&__maps.lock.word, &word, MUTEX_INC_DEPTH(word),
memory_order_relaxed, memory_order_relaxed))
return true;
continue;
}
#if DEBUG_MAPS_LOCK
if (__deadlock_tracked(&__maps.lock) == 1)
__maps_panic("error: maps lock already held\n");
if (__deadlock_check(&__maps.lock, 1))
__maps_panic("error: maps lock is cyclic\n");
#endif
word = 0;
lock = MUTEX_LOCK(word);
lock = MUTEX_SET_OWNER(lock, me);
if (atomic_compare_exchange_weak_explicit(&__maps.lock, &word, lock,
if (atomic_compare_exchange_weak_explicit(&__maps.lock.word, &word, lock,
memory_order_acquire,
memory_order_relaxed))
memory_order_relaxed)) {
#if DEBUG_MAPS_LOCK
__deadlock_track(&__maps.lock, 0);
__deadlock_record(&__maps.lock, 0);
#endif
return false;
}
for (;;) {
word = atomic_load_explicit(&__maps.lock, memory_order_relaxed);
word = atomic_load_explicit(&__maps.lock.word, memory_order_relaxed);
if (MUTEX_OWNER(word) == me)
break;
if (!word)
@ -127,7 +158,7 @@ privileged bool __maps_lock(void) {
}
}
privileged void __maps_unlock(void) {
ABI void __maps_unlock(void) {
int me;
uint64_t word;
struct CosmoTib *tib;
@ -140,16 +171,25 @@ privileged void __maps_unlock(void) {
me = atomic_load_explicit(&tib->tib_tid, memory_order_acquire);
if (me <= 0)
return;
word = atomic_load_explicit(&__maps.lock, memory_order_relaxed);
word = atomic_load_explicit(&__maps.lock.word, memory_order_relaxed);
#if DEBUG_MAPS_LOCK
if (__deadlock_tracked(&__maps.lock) == 0)
__maps_panic("error: maps lock not owned by caller\n");
#endif
for (;;) {
if (MUTEX_DEPTH(word)) {
if (atomic_compare_exchange_weak_explicit(
&__maps.lock, &word, MUTEX_DEC_DEPTH(word), memory_order_relaxed,
memory_order_relaxed))
&__maps.lock.word, &word, MUTEX_DEC_DEPTH(word),
memory_order_relaxed, memory_order_relaxed))
break;
}
if (atomic_compare_exchange_weak_explicit(
&__maps.lock, &word, 0, memory_order_release, memory_order_relaxed))
if (atomic_compare_exchange_weak_explicit(&__maps.lock.word, &word, 0,
memory_order_release,
memory_order_relaxed)) {
#if DEBUG_MAPS_LOCK
__deadlock_untrack(&__maps.lock);
#endif
break;
}
}
}