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lockmgr: rewrite upgrade to stop always dropping the lock

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This matches rw and sx locks.
This commit is contained in:
Mateusz Guzik 2020-07-21 14:41:25 +00:00
parent bdb6d824f4
commit f6b091fbbd
1 changed files with 34 additions and 36 deletions
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70
sys/kern/kern_lock.c
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@ -878,9 +878,8 @@ static __noinline int
lockmgr_upgrade(struct lock *lk, u_int flags, struct lock_object *ilk,
const char *file, int line, struct lockmgr_wait *lwa)
{
uintptr_t tid, x, v;
uintptr_t tid, v, setv;
int error = 0;
int wakeup_swapper = 0;
int op;
if (KERNEL_PANICKED())
@ -889,48 +888,47 @@ lockmgr_upgrade(struct lock *lk, u_int flags, struct lock_object *ilk,
tid = (uintptr_t)curthread;
_lockmgr_assert(lk, KA_SLOCKED, file, line);
v = lockmgr_read_value(lk);
x = v & LK_ALL_WAITERS;
v &= LK_EXCLUSIVE_SPINNERS;
/*
* Try to switch from one shared lock to an exclusive one.
* We need to preserve waiters flags during the operation.
*/
if (atomic_cmpset_ptr(&lk->lk_lock, LK_SHARERS_LOCK(1) | x | v,
tid | x)) {
LOCK_LOG_LOCK("XUPGRADE", &lk->lock_object, 0, 0, file,
line);
WITNESS_UPGRADE(&lk->lock_object, LOP_EXCLUSIVE |
LK_TRYWIT(flags), file, line);
LOCKSTAT_RECORD0(lockmgr__upgrade, lk);
TD_SLOCKS_DEC(curthread);
goto out;
}
op = flags & LK_TYPE_MASK;
v = lockmgr_read_value(lk);
for (;;) {
if (LK_SHARERS_LOCK(v) > 1) {
if (op == LK_TRYUPGRADE) {
LOCK_LOG2(lk, "%s: %p failed the nowait upgrade",
__func__, lk);
error = EBUSY;
goto out;
}
if (lockmgr_sunlock_try(lk, &v)) {
lockmgr_note_shared_release(lk, file, line);
goto out_xlock;
}
}
MPASS((v & ~LK_ALL_WAITERS) == LK_SHARERS_LOCK(1));
/*
* In LK_TRYUPGRADE mode, do not drop the lock,
* returning EBUSY instead.
*/
if (op == LK_TRYUPGRADE) {
LOCK_LOG2(lk, "%s: %p failed the nowait upgrade",
__func__, lk);
error = EBUSY;
goto out;
setv = tid;
setv |= (v & LK_ALL_WAITERS);
/*
* Try to switch from one shared lock to an exclusive one.
* We need to preserve waiters flags during the operation.
*/
if (atomic_fcmpset_ptr(&lk->lk_lock, &v, setv)) {
LOCK_LOG_LOCK("XUPGRADE", &lk->lock_object, 0, 0, file,
line);
WITNESS_UPGRADE(&lk->lock_object, LOP_EXCLUSIVE |
LK_TRYWIT(flags), file, line);
LOCKSTAT_RECORD0(lockmgr__upgrade, lk);
TD_SLOCKS_DEC(curthread);
goto out;
}
}
/*
* We have been unable to succeed in upgrading, so just
* give up the shared lock.
*/
lockmgr_note_shared_release(lk, file, line);
wakeup_swapper |= wakeupshlk(lk, file, line);
out_xlock:
error = lockmgr_xlock_hard(lk, flags, ilk, file, line, lwa);
flags &= ~LK_INTERLOCK;
out:
lockmgr_exit(flags, ilk, wakeup_swapper);
lockmgr_exit(flags, ilk, 0);
return (error);
}