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libthr rtld locks: do not leak URWLOCK_READ_WAITERS into child

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Since there is only the current thread in the child, no pending readers
exist.  Clear the bit, since it confuses future attempts to acquire
write ownership of the rtld locks, due to URWLOCK_PREFER_READERS flag.

To be future-proof, clear all state about pending writers and readers.

PR:	271490
Reported and tested by:	KJ Tsanaktsidis <kj@kjtsanaktsidis.id.au>
Reviewed by:	markj
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D40178
This commit is contained in:
Konstantin Belousov 2023-05-20 11:11:54 +03:00
parent 54418f79fd
commit 6f49eafb05
3 changed files with 17 additions and 0 deletions
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4
lib/libthr/thread/thr_fork.c
View file

@ -78,6 +78,8 @@ __FBSDID("$FreeBSD$");
__weak_reference(_thr_atfork, _pthread_atfork);
__weak_reference(_thr_atfork, pthread_atfork);
bool _thr_after_fork = false;
int
_thr_atfork(void (*prepare)(void), void (*parent)(void),
void (*child)(void))
@ -243,7 +245,9 @@ thr_fork_impl(const struct thr_fork_args *a)
_thr_signal_postfork_child();
if (was_threaded) {
_thr_after_fork = true;
_rtld_atfork_post(rtld_locks);
_thr_after_fork = false;
__thr_pshared_atfork_post();
}
_thr_setthreaded(0);

2
lib/libthr/thread/thr_private.h
View file

@ -779,6 +779,8 @@ extern int _suspend_all_waiters __hidden;
extern int _suspend_all_cycle __hidden;
extern struct pthread *_single_thread __hidden;
extern bool _thr_after_fork __hidden;
/*
* Function prototype definitions.
*/

11
lib/libthr/thread/thr_rtld.c
View file

@ -158,6 +158,17 @@ _thr_rtld_lock_release(void *lock)
l = (struct rtld_lock *)lock;
state = l->lock.rw_state;
if (__predict_false(_thr_after_fork)) {
/*
* After fork, only this thread is running, there is no
* waiters. Keeping waiters recorded in rwlock breaks
* wake logic.
*/
atomic_clear_int(&l->lock.rw_state,
URWLOCK_WRITE_WAITERS | URWLOCK_READ_WAITERS);
l->lock.rw_blocked_readers = 0;
l->lock.rw_blocked_writers = 0;
}
if (_thr_rwlock_unlock(&l->lock) == 0) {
if ((state & URWLOCK_WRITE_OWNER) == 0)
curthread->rdlock_count--;