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locks: add a runtime check for missing turnstile

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There are sometimes bugs which result in the unlock fast path failing,
which in turns causes a not-helpful crash report when dereferencing a
NULL turnstile. Help debugging such cases by pointing out what happened
along with some debug.

Sponsored by:	Rubicon Communications, LLC ("Netgate")
This commit is contained in:
Mateusz Guzik 2024-07-11 00:17:27 +00:00
parent af84665261
commit 87ee63bac6
2 changed files with 15 additions and 5 deletions
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4
sys/kern/kern_mutex.c
View file

@ -1053,7 +1053,9 @@ __mtx_unlock_sleep(volatile uintptr_t *c, uintptr_t v)
turnstile_chain_lock(&m->lock_object);
_mtx_release_lock_quick(m);
ts = turnstile_lookup(&m->lock_object);
MPASS(ts != NULL);
if (__predict_false(ts == NULL)) {
panic("got NULL turnstile on mutex %p v %zx", m, v);
}
if (LOCK_LOG_TEST(&m->lock_object, opts))
CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p contested", m);
turnstile_broadcast(ts, TS_EXCLUSIVE_QUEUE);

16
sys/kern/kern_rwlock.c
View file

@ -770,11 +770,12 @@ __rw_runlock_hard(struct rwlock *rw, struct thread *td, uintptr_t v
LOCK_FILE_LINE_ARG_DEF)
{
struct turnstile *ts;
uintptr_t setv, queue;
uintptr_t setv, passedv, queue;
if (SCHEDULER_STOPPED())
return;
passedv = v;
if (__rw_runlock_try(rw, td, &v))
goto out_lockstat;
@ -827,7 +828,10 @@ __rw_runlock_hard(struct rwlock *rw, struct thread *td, uintptr_t v
* release the lock.
*/
ts = turnstile_lookup(&rw->lock_object);
MPASS(ts != NULL);
if (__predict_false(ts == NULL)) {
panic("got NULL turnstile on rwlock %p passedv %zx v %zx",
rw, passedv, v);
}
turnstile_broadcast(ts, queue);
turnstile_unpend(ts);
td->td_rw_rlocks--;
@ -1206,7 +1210,7 @@ __rw_wunlock_hard(volatile uintptr_t *c, uintptr_t v LOCK_FILE_LINE_ARG_DEF)
{
struct rwlock *rw;
struct turnstile *ts;
uintptr_t tid, setv;
uintptr_t tid, setv, passedv;
int queue;
tid = (uintptr_t)curthread;
@ -1254,6 +1258,7 @@ __rw_wunlock_hard(volatile uintptr_t *c, uintptr_t v LOCK_FILE_LINE_ARG_DEF)
* of waiters or doing some complicated lock handoff gymnastics.
*/
setv = RW_UNLOCKED;
passedv = v;
v = RW_READ_VALUE(rw);
queue = TS_SHARED_QUEUE;
if (v & RW_LOCK_WRITE_WAITERS) {
@ -1268,7 +1273,10 @@ __rw_wunlock_hard(volatile uintptr_t *c, uintptr_t v LOCK_FILE_LINE_ARG_DEF)
queue == TS_SHARED_QUEUE ? "read" : "write");
ts = turnstile_lookup(&rw->lock_object);
MPASS(ts != NULL);
if (__predict_false(ts == NULL)) {
panic("got NULL turnstile on rwlock %p passedv %zx v %zx", rw,
passedv, v);
}
turnstile_broadcast(ts, queue);
turnstile_unpend(ts);
turnstile_chain_unlock(&rw->lock_object);