From 2fe7e6f7c9f55eac24c5b3cdf56af29ab9b0ca81 Mon Sep 17 00:00:00 2001 From: Roland Dreier Date: Fri, 25 Jan 2008 14:15:42 -0800 Subject: [PATCH] IB/umad: Simplify and fix locking In addition to being overly complex, the locking in user_mad.c is broken: there were multiple reports of deadlocks and lockdep warnings. In particular it seems that a single thread may end up trying to take the same rwsem for reading more than once, which is explicitly forbidden in the comments in . To solve this, we change the locking to use plain mutexes instead of rwsems. There is one mutex per open file, which protects the contents of the struct ib_umad_file, including the array of agents and list of queued packets; and there is one mutex per struct ib_umad_port, which protects the contents, including the list of open files. We never hold the file mutex across calls to functions like ib_unregister_mad_agent(), which can call back into other ib_umad code to queue a packet, and we always hold the port mutex as long as we need to make sure that a device is not hot-unplugged from under us. This even makes things nicer for users of the -rt patch, since we remove calls to downgrade_write() (which is not implemented in -rt). Signed-off-by: Roland Dreier --- drivers/infiniband/core/user_mad.c | 115 +++++++++++++---------------- 1 file changed, 53 insertions(+), 62 deletions(-) diff --git a/drivers/infiniband/core/user_mad.c b/drivers/infiniband/core/user_mad.c index b53eac4611..4e915104ac 100644 --- a/drivers/infiniband/core/user_mad.c +++ b/drivers/infiniband/core/user_mad.c @@ -2,6 +2,7 @@ * Copyright (c) 2004 Topspin Communications. All rights reserved. * Copyright (c) 2005 Voltaire, Inc. All rights reserved. * Copyright (c) 2005 Sun Microsystems, Inc. All rights reserved. + * Copyright (c) 2008 Cisco. All rights reserved. * * This software is available to you under a choice of one of two * licenses. You may choose to be licensed under the terms of the GNU @@ -42,7 +43,7 @@ #include #include #include -#include +#include #include #include @@ -94,7 +95,7 @@ struct ib_umad_port { struct class_device *sm_class_dev; struct semaphore sm_sem; - struct rw_semaphore mutex; + struct mutex file_mutex; struct list_head file_list; struct ib_device *ib_dev; @@ -110,11 +111,11 @@ struct ib_umad_device { }; struct ib_umad_file { + struct mutex mutex; struct ib_umad_port *port; struct list_head recv_list; struct list_head send_list; struct list_head port_list; - spinlock_t recv_lock; spinlock_t send_lock; wait_queue_head_t recv_wait; struct ib_mad_agent *agent[IB_UMAD_MAX_AGENTS]; @@ -156,7 +157,7 @@ static int hdr_size(struct ib_umad_file *file) sizeof (struct ib_user_mad_hdr_old); } -/* caller must hold port->mutex at least for reading */ +/* caller must hold file->mutex */ static struct ib_mad_agent *__get_agent(struct ib_umad_file *file, int id) { return file->agents_dead ? NULL : file->agent[id]; @@ -168,32 +169,30 @@ static int queue_packet(struct ib_umad_file *file, { int ret = 1; - down_read(&file->port->mutex); + mutex_lock(&file->mutex); for (packet->mad.hdr.id = 0; packet->mad.hdr.id < IB_UMAD_MAX_AGENTS; packet->mad.hdr.id++) if (agent == __get_agent(file, packet->mad.hdr.id)) { - spin_lock_irq(&file->recv_lock); list_add_tail(&packet->list, &file->recv_list); - spin_unlock_irq(&file->recv_lock); wake_up_interruptible(&file->recv_wait); ret = 0; break; } - up_read(&file->port->mutex); + mutex_unlock(&file->mutex); return ret; } static void dequeue_send(struct ib_umad_file *file, struct ib_umad_packet *packet) - { +{ spin_lock_irq(&file->send_lock); list_del(&packet->list); spin_unlock_irq(&file->send_lock); - } +} static void send_handler(struct ib_mad_agent *agent, struct ib_mad_send_wc *send_wc) @@ -341,10 +340,10 @@ static ssize_t ib_umad_read(struct file *filp, char __user *buf, if (count < hdr_size(file)) return -EINVAL; - spin_lock_irq(&file->recv_lock); + mutex_lock(&file->mutex); while (list_empty(&file->recv_list)) { - spin_unlock_irq(&file->recv_lock); + mutex_unlock(&file->mutex); if (filp->f_flags & O_NONBLOCK) return -EAGAIN; @@ -353,13 +352,13 @@ static ssize_t ib_umad_read(struct file *filp, char __user *buf, !list_empty(&file->recv_list))) return -ERESTARTSYS; - spin_lock_irq(&file->recv_lock); + mutex_lock(&file->mutex); } packet = list_entry(file->recv_list.next, struct ib_umad_packet, list); list_del(&packet->list); - spin_unlock_irq(&file->recv_lock); + mutex_unlock(&file->mutex); if (packet->recv_wc) ret = copy_recv_mad(file, buf, packet, count); @@ -368,9 +367,9 @@ static ssize_t ib_umad_read(struct file *filp, char __user *buf, if (ret < 0) { /* Requeue packet */ - spin_lock_irq(&file->recv_lock); + mutex_lock(&file->mutex); list_add(&packet->list, &file->recv_list); - spin_unlock_irq(&file->recv_lock); + mutex_unlock(&file->mutex); } else { if (packet->recv_wc) ib_free_recv_mad(packet->recv_wc); @@ -481,7 +480,7 @@ static ssize_t ib_umad_write(struct file *filp, const char __user *buf, goto err; } - down_read(&file->port->mutex); + mutex_lock(&file->mutex); agent = __get_agent(file, packet->mad.hdr.id); if (!agent) { @@ -577,7 +576,7 @@ static ssize_t ib_umad_write(struct file *filp, const char __user *buf, if (ret) goto err_send; - up_read(&file->port->mutex); + mutex_unlock(&file->mutex); return count; err_send: @@ -587,7 +586,7 @@ err_msg: err_ah: ib_destroy_ah(ah); err_up: - up_read(&file->port->mutex); + mutex_unlock(&file->mutex); err: kfree(packet); return ret; @@ -613,11 +612,12 @@ static int ib_umad_reg_agent(struct ib_umad_file *file, void __user *arg, { struct ib_user_mad_reg_req ureq; struct ib_mad_reg_req req; - struct ib_mad_agent *agent; + struct ib_mad_agent *agent = NULL; int agent_id; int ret; - down_write(&file->port->mutex); + mutex_lock(&file->port->file_mutex); + mutex_lock(&file->mutex); if (!file->port->ib_dev) { ret = -EPIPE; @@ -666,13 +666,13 @@ found: send_handler, recv_handler, file); if (IS_ERR(agent)) { ret = PTR_ERR(agent); + agent = NULL; goto out; } if (put_user(agent_id, (u32 __user *) (arg + offsetof(struct ib_user_mad_reg_req, id)))) { ret = -EFAULT; - ib_unregister_mad_agent(agent); goto out; } @@ -690,7 +690,13 @@ found: ret = 0; out: - up_write(&file->port->mutex); + mutex_unlock(&file->mutex); + + if (ret && agent) + ib_unregister_mad_agent(agent); + + mutex_unlock(&file->port->file_mutex); + return ret; } @@ -703,7 +709,8 @@ static int ib_umad_unreg_agent(struct ib_umad_file *file, u32 __user *arg) if (get_user(id, arg)) return -EFAULT; - down_write(&file->port->mutex); + mutex_lock(&file->port->file_mutex); + mutex_lock(&file->mutex); if (id < 0 || id >= IB_UMAD_MAX_AGENTS || !__get_agent(file, id)) { ret = -EINVAL; @@ -714,11 +721,13 @@ static int ib_umad_unreg_agent(struct ib_umad_file *file, u32 __user *arg) file->agent[id] = NULL; out: - up_write(&file->port->mutex); + mutex_unlock(&file->mutex); if (agent) ib_unregister_mad_agent(agent); + mutex_unlock(&file->port->file_mutex); + return ret; } @@ -726,12 +735,12 @@ static long ib_umad_enable_pkey(struct ib_umad_file *file) { int ret = 0; - down_write(&file->port->mutex); + mutex_lock(&file->mutex); if (file->already_used) ret = -EINVAL; else file->use_pkey_index = 1; - up_write(&file->port->mutex); + mutex_unlock(&file->mutex); return ret; } @@ -783,7 +792,7 @@ static int ib_umad_open(struct inode *inode, struct file *filp) if (!port) return -ENXIO; - down_write(&port->mutex); + mutex_lock(&port->file_mutex); if (!port->ib_dev) { ret = -ENXIO; @@ -797,7 +806,7 @@ static int ib_umad_open(struct inode *inode, struct file *filp) goto out; } - spin_lock_init(&file->recv_lock); + mutex_init(&file->mutex); spin_lock_init(&file->send_lock); INIT_LIST_HEAD(&file->recv_list); INIT_LIST_HEAD(&file->send_list); @@ -809,7 +818,7 @@ static int ib_umad_open(struct inode *inode, struct file *filp) list_add_tail(&file->port_list, &port->file_list); out: - up_write(&port->mutex); + mutex_unlock(&port->file_mutex); return ret; } @@ -821,7 +830,8 @@ static int ib_umad_close(struct inode *inode, struct file *filp) int already_dead; int i; - down_write(&file->port->mutex); + mutex_lock(&file->port->file_mutex); + mutex_lock(&file->mutex); already_dead = file->agents_dead; file->agents_dead = 1; @@ -834,14 +844,14 @@ static int ib_umad_close(struct inode *inode, struct file *filp) list_del(&file->port_list); - downgrade_write(&file->port->mutex); + mutex_unlock(&file->mutex); if (!already_dead) for (i = 0; i < IB_UMAD_MAX_AGENTS; ++i) if (file->agent[i]) ib_unregister_mad_agent(file->agent[i]); - up_read(&file->port->mutex); + mutex_unlock(&file->port->file_mutex); kfree(file); kref_put(&dev->ref, ib_umad_release_dev); @@ -914,10 +924,10 @@ static int ib_umad_sm_close(struct inode *inode, struct file *filp) }; int ret = 0; - down_write(&port->mutex); + mutex_lock(&port->file_mutex); if (port->ib_dev) ret = ib_modify_port(port->ib_dev, port->port_num, 0, &props); - up_write(&port->mutex); + mutex_unlock(&port->file_mutex); up(&port->sm_sem); @@ -981,7 +991,7 @@ static int ib_umad_init_port(struct ib_device *device, int port_num, port->ib_dev = device; port->port_num = port_num; init_MUTEX(&port->sm_sem); - init_rwsem(&port->mutex); + mutex_init(&port->file_mutex); INIT_LIST_HEAD(&port->file_list); port->dev = cdev_alloc(); @@ -1052,6 +1062,7 @@ err_cdev: static void ib_umad_kill_port(struct ib_umad_port *port) { struct ib_umad_file *file; + int already_dead; int id; class_set_devdata(port->class_dev, NULL); @@ -1067,42 +1078,22 @@ static void ib_umad_kill_port(struct ib_umad_port *port) umad_port[port->dev_num] = NULL; spin_unlock(&port_lock); - down_write(&port->mutex); + mutex_lock(&port->file_mutex); port->ib_dev = NULL; - /* - * Now go through the list of files attached to this port and - * unregister all of their MAD agents. We need to hold - * port->mutex while doing this to avoid racing with - * ib_umad_close(), but we can't hold the mutex for writing - * while calling ib_unregister_mad_agent(), since that might - * deadlock by calling back into queue_packet(). So we - * downgrade our lock to a read lock, and then drop and - * reacquire the write lock for the next iteration. - * - * We do list_del_init() on the file's list_head so that the - * list_del in ib_umad_close() is still OK, even after the - * file is removed from the list. - */ - while (!list_empty(&port->file_list)) { - file = list_entry(port->file_list.next, struct ib_umad_file, - port_list); - + list_for_each_entry(file, &port->file_list, port_list) { + mutex_lock(&file->mutex); + already_dead = file->agents_dead; file->agents_dead = 1; - list_del_init(&file->port_list); - - downgrade_write(&port->mutex); + mutex_unlock(&file->mutex); for (id = 0; id < IB_UMAD_MAX_AGENTS; ++id) if (file->agent[id]) ib_unregister_mad_agent(file->agent[id]); - - up_read(&port->mutex); - down_write(&port->mutex); } - up_write(&port->mutex); + mutex_unlock(&port->file_mutex); clear_bit(port->dev_num, dev_map); } -- 2.39.5