/* rwsem-spinlock.c: R/W semaphores: contention handling functions for * generic spinlock implementation * * Copyright (c) 2001 David Howells (dhowells@redhat.com). * - Derived partially from idea by Andrea Arcangeli * - Derived also from comments by Linus */ #include #include #include enum rwsem_waiter_type { RWSEM_WAITING_FOR_WRITE, RWSEM_WAITING_FOR_READ }; struct rwsem_waiter { struct list_head list; struct task_struct *task; enum rwsem_waiter_type type; }; int rwsem_is_locked(struct rw_semaphore *sem) { int ret = 1; unsigned long flags; if (raw_spin_trylock_irqsave(&sem->wait_lock, flags)) { ret = (sem->count != 0); raw_spin_unlock_irqrestore(&sem->wait_lock, flags); } return ret; } EXPORT_SYMBOL(rwsem_is_locked); /* * initialise the semaphore */ void __init_rwsem(struct rw_semaphore *sem, const char *name, struct lock_class_key *key) { #ifdef CONFIG_DEBUG_LOCK_ALLOC /* * Make sure we are not reinitializing a held semaphore: */ debug_check_no_locks_freed((void *)sem, sizeof(*sem)); lockdep_init_map(&sem->dep_map, name, key, 0); #endif sem->count = 0; raw_spin_lock_init(&sem->wait_lock); INIT_LIST_HEAD(&sem->wait_list); } EXPORT_SYMBOL(__init_rwsem); /* * handle the lock release when processes blocked on it that can now run * - if we come here, then: * - the 'active count' _reached_ zero * - the 'waiting count' is non-zero * - the spinlock must be held by the caller * - woken process blocks are discarded from the list after having task zeroed * - writers are only woken if wakewrite is non-zero */ static inline struct rw_semaphore * __rwsem_do_wake(struct rw_semaphore *sem, int wakewrite) { struct rwsem_waiter *waiter; struct task_struct *tsk; int woken; waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list); if (waiter->type == RWSEM_WAITING_FOR_WRITE) { if (wakewrite) /* Wake up a writer. Note that we do not grant it the * lock - it will have to acquire it when it runs. */ wake_up_process(waiter->task); goto out; } /* grant an infinite number of read locks to the front of the queue */ woken = 0; do { struct list_head *next = waiter->list.next; list_del(&waiter->list); tsk = waiter->task; /* * Make sure we do not wakeup the next reader before * setting the nil condition to grant the next reader; * otherwise we could miss the wakeup on the other * side and end up sleeping again. See the pairing * in rwsem_down_read_failed(). */ smp_mb(); waiter->task = NULL; wake_up_process(tsk); put_task_struct(tsk); woken++; if (next == &sem->wait_list) break; waiter = list_entry(next, struct rwsem_waiter, list); } while (waiter->type != RWSEM_WAITING_FOR_WRITE); sem->count += woken; out: return sem; } /* * wake a single writer */ static inline struct rw_semaphore * __rwsem_wake_one_writer(struct rw_semaphore *sem) { struct rwsem_waiter *waiter; waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list); wake_up_process(waiter->task); return sem; } /* * get a read lock on the semaphore */ void __sched __down_read(struct rw_semaphore *sem) { struct rwsem_waiter waiter; struct task_struct *tsk; unsigned long flags; raw_spin_lock_irqsave(&sem->wait_lock, flags); if (sem->count >= 0 && list_empty(&sem->wait_list)) { /* granted */ sem->count++; raw_spin_unlock_irqrestore(&sem->wait_lock, flags); goto out; } tsk = current; set_task_state(tsk, TASK_UNINTERRUPTIBLE); /* set up my own style of waitqueue */ waiter.task = tsk; waiter.type = RWSEM_WAITING_FOR_READ; get_task_struct(tsk); list_add_tail(&waiter.list, &sem->wait_list); /* we don't need to touch the semaphore struct anymore */ raw_spin_unlock_irqrestore(&sem->wait_lock, flags); /* wait to be given the lock */ for (;;) { if (!waiter.task) break; schedule(); set_task_state(tsk, TASK_UNINTERRUPTIBLE); } __set_task_state(tsk, TASK_RUNNING); out: ; } /* * trylock for reading -- returns 1 if successful, 0 if contention */ int __down_read_trylock(struct rw_semaphore *sem) { unsigned long flags; int ret = 0; raw_spin_lock_irqsave(&sem->wait_lock, flags); if (sem->count >= 0 && list_empty(&sem->wait_list)) { /* granted */ sem->count++; ret = 1; } raw_spin_unlock_irqrestore(&sem->wait_lock, flags); return ret; } /* * get a write lock on the semaphore */ int __sched __down_write_common(struct rw_semaphore *sem, int state) { struct rwsem_waiter waiter; struct task_struct *tsk; unsigned long flags; int ret = 0; raw_spin_lock_irqsave(&sem->wait_lock, flags); /* set up my own style of waitqueue */ tsk = current; waiter.task = tsk; waiter.type = RWSEM_WAITING_FOR_WRITE; list_add_tail(&waiter.list, &sem->wait_list); /* wait for someone to release the lock */ for (;;) { /* * That is the key to support write lock stealing: allows the * task already on CPU to get the lock soon rather than put * itself into sleep and waiting for system woke it or someone * else in the head of the wait list up. */ if (sem->count == 0) break; if (signal_pending_state(state, current)) { ret = -EINTR; goto out; } set_task_state(tsk, state); raw_spin_unlock_irqrestore(&sem->wait_lock, flags); schedule(); raw_spin_lock_irqsave(&sem->wait_lock, flags); } /* got the lock */ sem->count = -1; out: list_del(&waiter.list); raw_spin_unlock_irqrestore(&sem->wait_lock, flags); return ret; } void __sched __down_write(struct rw_semaphore *sem) { __down_write_common(sem, TASK_UNINTERRUPTIBLE); } int __sched __down_write_killable(struct rw_semaphore *sem) { return __down_write_common(sem, TASK_KILLABLE); } /* * trylock for writing -- returns 1 if successful, 0 if contention */ int __down_write_trylock(struct rw_semaphore *sem) { unsigned long flags; int ret = 0; raw_spin_lock_irqsave(&sem->wait_lock, flags); if (sem->count == 0) { /* got the lock */ sem->count = -1; ret = 1; } raw_spin_unlock_irqrestore(&sem->wait_lock, flags); return ret; } /* * release a read lock on the semaphore */ void __up_read(struct rw_semaphore *sem) { unsigned long flags; raw_spin_lock_irqsave(&sem->wait_lock, flags); if (--sem->count == 0 && !list_empty(&sem->wait_list)) sem = __rwsem_wake_one_writer(sem); raw_spin_unlock_irqrestore(&sem->wait_lock, flags); } /* * release a write lock on the semaphore */ void __up_write(struct rw_semaphore *sem) { unsigned long flags; raw_spin_lock_irqsave(&sem->wait_lock, flags); sem->count = 0; if (!list_empty(&sem->wait_list)) sem = __rwsem_do_wake(sem, 1); raw_spin_unlock_irqrestore(&sem->wait_lock, flags); } /* * downgrade a write lock into a read lock * - just wake up any readers at the front of the queue */ void __downgrade_write(struct rw_semaphore *sem) { unsigned long flags; raw_spin_lock_irqsave(&sem->wait_lock, flags); sem->count = 1; if (!list_empty(&sem->wait_list)) sem = __rwsem_do_wake(sem, 0); raw_spin_unlock_irqrestore(&sem->wait_lock, flags); } e setup and handling of the queued traps once in the kernel. This patch series addresses both of these issues. The queues are fixed by simply zeroing the memory before use. PIO errors from userspace will result in a SIGBUS being sent to the user process. The MEM errors form userspace will result in a SIGKILL and also cause the offending pages to be claimed so they are no longer used in future tasks. SIGKILL is used to ensure that the process does not try to coredump and result in an attempt to read the memory again from within kernel space. Although there is a HV call to scrub the memory (mem_scrub), there is no easy way to guarantee that the real memory address(es) are not used by other tasks. Clearing the error with mem_scrub would zero the memory and cause the other processes to proceed with bad data. The handling of other non-resumable errors remain unchanged and will cause a panic. ==================== Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'tools/virtio/Makefile')