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Fix two issues with the spin loops in the umtx(2) implementation.
- When looping, check for the pending suspension. Otherwise, other usermode thread which races with the looping one, could try to prevent the process from stopping or exiting. - Add missed checks for the faults from casuword*(). The code is structured in a way which makes the loops exit if the specified address is invalid, since both fuword() and casuword() return -1 on the fault. But if the address is mapped readonly, the typical value read by fuword() is different from -1, while casuword() returns -1. Absent the checks for casuword() faults, this is interpreted as the race with other thread and causes non-interruptible spinning in the kernel. Reported and tested by: pho Sponsored by: The FreeBSD Foundation MFC after: 2 weeks
This commit is contained in:
Konstantin Belousov
parent
967206bde7
commit
1d7466bca4
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=251684
@ -628,6 +628,32 @@ umtxq_count_pi(struct umtx_key *key, struct umtx_q **first)
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return (0);
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}
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static int
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umtxq_check_susp(struct thread *td)
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{
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struct proc *p;
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int error;
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/*
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* The check for TDF_NEEDSUSPCHK is racy, but it is enough to
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* eventually break the lockstep loop.
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*/
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if ((td->td_flags & TDF_NEEDSUSPCHK) == 0)
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return (0);
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error = 0;
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p = td->td_proc;
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PROC_LOCK(p);
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if (P_SHOULDSTOP(p) ||
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((p->p_flag & P_TRACED) && (td->td_dbgflags & TDB_SUSPEND))) {
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if (p->p_flag & P_SINGLE_EXIT)
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error = EINTR;
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else
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error = ERESTART;
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}
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PROC_UNLOCK(p);
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return (error);
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}
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/*
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* Wake up threads waiting on an userland object.
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*/
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@ -858,6 +884,10 @@ do_lock_umtx(struct thread *td, struct umtx *umtx, u_long id,
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if (owner == -1)
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return (EFAULT);
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error = umtxq_check_susp(td);
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if (error != 0)
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break;
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/* If this failed the lock has changed, restart. */
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continue;
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}
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@ -908,6 +938,9 @@ do_lock_umtx(struct thread *td, struct umtx *umtx, u_long id,
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umtxq_remove(uq);
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umtxq_unlock(&uq->uq_key);
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umtx_key_release(&uq->uq_key);
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if (error == 0)
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error = umtxq_check_susp(td);
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}
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if (timeout == NULL) {
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@ -1032,6 +1065,10 @@ do_lock_umtx32(struct thread *td, uint32_t *m, uint32_t id,
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if (owner == -1)
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return (EFAULT);
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error = umtxq_check_susp(td);
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if (error != 0)
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break;
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/* If this failed the lock has changed, restart. */
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continue;
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}
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@ -1082,6 +1119,9 @@ do_lock_umtx32(struct thread *td, uint32_t *m, uint32_t id,
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umtxq_remove(uq);
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umtxq_unlock(&uq->uq_key);
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umtx_key_release(&uq->uq_key);
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if (error == 0)
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error = umtxq_check_susp(td);
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}
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if (timeout == NULL) {
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@ -1272,6 +1312,10 @@ do_lock_normal(struct thread *td, struct umutex *m, uint32_t flags,
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if (owner == -1)
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return (EFAULT);
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error = umtxq_check_susp(td);
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if (error != 0)
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return (error);
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/* If this failed the lock has changed, restart. */
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continue;
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}
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@ -1331,6 +1375,9 @@ do_lock_normal(struct thread *td, struct umutex *m, uint32_t flags,
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umtxq_remove(uq);
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umtxq_unlock(&uq->uq_key);
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umtx_key_release(&uq->uq_key);
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if (error == 0)
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error = umtxq_check_susp(td);
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}
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return (0);
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@ -1487,6 +1534,11 @@ do_wake2_umutex(struct thread *td, struct umutex *m, uint32_t flags)
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if (old == owner)
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break;
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owner = old;
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if (old == -1)
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break;
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error = umtxq_check_susp(td);
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if (error != 0)
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break;
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}
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} else if (count == 1) {
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owner = fuword32(__DEVOLATILE(uint32_t *, &m->m_owner));
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@ -1497,6 +1549,11 @@ do_wake2_umutex(struct thread *td, struct umutex *m, uint32_t flags)
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if (old == owner)
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break;
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owner = old;
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if (old == -1)
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break;
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error = umtxq_check_susp(td);
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if (error != 0)
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break;
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}
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}
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umtxq_lock(&key);
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@ -1961,6 +2018,10 @@ do_lock_pi(struct thread *td, struct umutex *m, uint32_t flags,
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break;
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}
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error = umtxq_check_susp(td);
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if (error != 0)
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break;
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/* If this failed the lock has changed, restart. */
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continue;
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}
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@ -2017,6 +2078,10 @@ do_lock_pi(struct thread *td, struct umutex *m, uint32_t flags,
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umtxq_unbusy(&uq->uq_key);
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umtxq_unlock(&uq->uq_key);
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}
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error = umtxq_check_susp(td);
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if (error != 0)
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break;
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}
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umtxq_lock(&uq->uq_key);
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@ -2663,10 +2728,17 @@ do_rw_rdlock(struct thread *td, struct urwlock *rwlock, long fflag, struct _umtx
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return (EAGAIN);
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}
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oldstate = casuword32(&rwlock->rw_state, state, state + 1);
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if (oldstate == -1) {
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umtx_key_release(&uq->uq_key);
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return (EFAULT);
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}
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if (oldstate == state) {
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umtx_key_release(&uq->uq_key);
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return (0);
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}
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error = umtxq_check_susp(td);
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if (error != 0)
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break;
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state = oldstate;
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}
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@ -2687,9 +2759,22 @@ do_rw_rdlock(struct thread *td, struct urwlock *rwlock, long fflag, struct _umtx
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/* set read contention bit */
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while ((state & wrflags) && !(state & URWLOCK_READ_WAITERS)) {
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oldstate = casuword32(&rwlock->rw_state, state, state | URWLOCK_READ_WAITERS);
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if (oldstate == -1) {
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error = EFAULT;
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break;
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}
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if (oldstate == state)
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goto sleep;
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state = oldstate;
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error = umtxq_check_susp(td);
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if (error != 0)
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break;
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}
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if (error != 0) {
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umtxq_lock(&uq->uq_key);
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umtxq_unbusy(&uq->uq_key);
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umtxq_unlock(&uq->uq_key);
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break;
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}
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/* state is changed while setting flags, restart */
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@ -2697,6 +2782,9 @@ do_rw_rdlock(struct thread *td, struct urwlock *rwlock, long fflag, struct _umtx
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umtxq_lock(&uq->uq_key);
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umtxq_unbusy(&uq->uq_key);
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umtxq_unlock(&uq->uq_key);
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error = umtxq_check_susp(td);
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if (error != 0)
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break;
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continue;
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}
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@ -2729,15 +2817,24 @@ do_rw_rdlock(struct thread *td, struct urwlock *rwlock, long fflag, struct _umtx
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for (;;) {
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oldstate = casuword32(&rwlock->rw_state, state,
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state & ~URWLOCK_READ_WAITERS);
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if (oldstate == -1) {
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error = EFAULT;
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break;
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}
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if (oldstate == state)
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break;
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state = oldstate;
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error = umtxq_check_susp(td);
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if (error != 0)
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break;
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}
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}
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umtxq_lock(&uq->uq_key);
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umtxq_unbusy(&uq->uq_key);
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umtxq_unlock(&uq->uq_key);
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if (error != 0)
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break;
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}
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umtx_key_release(&uq->uq_key);
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if (error == ERESTART)
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@ -2770,11 +2867,18 @@ do_rw_wrlock(struct thread *td, struct urwlock *rwlock, struct _umtx_time *timeo
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state = fuword32(__DEVOLATILE(int32_t *, &rwlock->rw_state));
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while (!(state & URWLOCK_WRITE_OWNER) && URWLOCK_READER_COUNT(state) == 0) {
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oldstate = casuword32(&rwlock->rw_state, state, state | URWLOCK_WRITE_OWNER);
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if (oldstate == -1) {
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umtx_key_release(&uq->uq_key);
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return (EFAULT);
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}
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if (oldstate == state) {
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umtx_key_release(&uq->uq_key);
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return (0);
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}
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state = oldstate;
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error = umtxq_check_susp(td);
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if (error != 0)
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break;
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}
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if (error) {
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@ -2804,15 +2908,31 @@ do_rw_wrlock(struct thread *td, struct urwlock *rwlock, struct _umtx_time *timeo
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while (((state & URWLOCK_WRITE_OWNER) || URWLOCK_READER_COUNT(state) != 0) &&
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(state & URWLOCK_WRITE_WAITERS) == 0) {
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oldstate = casuword32(&rwlock->rw_state, state, state | URWLOCK_WRITE_WAITERS);
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if (oldstate == -1) {
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error = EFAULT;
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break;
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}
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if (oldstate == state)
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goto sleep;
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state = oldstate;
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error = umtxq_check_susp(td);
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if (error != 0)
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break;
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}
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if (error != 0) {
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umtxq_lock(&uq->uq_key);
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umtxq_unbusy(&uq->uq_key);
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umtxq_unlock(&uq->uq_key);
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break;
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}
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if (!(state & URWLOCK_WRITE_OWNER) && URWLOCK_READER_COUNT(state) == 0) {
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umtxq_lock(&uq->uq_key);
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umtxq_unbusy(&uq->uq_key);
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umtxq_unlock(&uq->uq_key);
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error = umtxq_check_susp(td);
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if (error != 0)
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break;
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continue;
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}
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sleep:
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@ -2842,9 +2962,21 @@ do_rw_wrlock(struct thread *td, struct urwlock *rwlock, struct _umtx_time *timeo
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for (;;) {
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oldstate = casuword32(&rwlock->rw_state, state,
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state & ~URWLOCK_WRITE_WAITERS);
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if (oldstate == -1) {
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error = EFAULT;
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break;
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}
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if (oldstate == state)
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break;
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state = oldstate;
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error = umtxq_check_susp(td);
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/*
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* We are leaving the URWLOCK_WRITE_WAITERS
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* behind, but this should not harm the
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* correctness.
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*/
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if (error != 0)
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break;
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}
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blocked_readers = fuword32(&rwlock->rw_blocked_readers);
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} else
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@ -2880,12 +3012,19 @@ do_rw_unlock(struct thread *td, struct urwlock *rwlock)
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for (;;) {
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oldstate = casuword32(&rwlock->rw_state, state,
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state & ~URWLOCK_WRITE_OWNER);
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if (oldstate == -1) {
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error = EFAULT;
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goto out;
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}
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if (oldstate != state) {
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state = oldstate;
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if (!(oldstate & URWLOCK_WRITE_OWNER)) {
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error = EPERM;
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goto out;
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}
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error = umtxq_check_susp(td);
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if (error != 0)
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goto out;
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} else
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break;
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}
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@ -2893,14 +3032,20 @@ do_rw_unlock(struct thread *td, struct urwlock *rwlock)
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for (;;) {
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oldstate = casuword32(&rwlock->rw_state, state,
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state - 1);
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if (oldstate == -1) {
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error = EFAULT;
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goto out;
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}
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if (oldstate != state) {
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state = oldstate;
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if (URWLOCK_READER_COUNT(oldstate) == 0) {
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error = EPERM;
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goto out;
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}
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}
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else
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error = umtxq_check_susp(td);
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if (error != 0)
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goto out;
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} else
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break;
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}
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} else {
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