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IB/umad: Simplify and fix locking
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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 <linux/rwsem.h>.

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 <rolandd@cisco.com>
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Roland Dreier committed Jan 25, 2008
1 parent cf9542a commit 2fe7e6f
Showing 1 changed file with 53 additions and 62 deletions.
115 changes: 53 additions & 62 deletions drivers/infiniband/core/user_mad.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand Down Expand Up @@ -42,7 +43,7 @@
#include <linux/cdev.h>
#include <linux/dma-mapping.h>
#include <linux/poll.h>
#include <linux/rwsem.h>
#include <linux/mutex.h>
#include <linux/kref.h>
#include <linux/compat.h>

Expand Down Expand Up @@ -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;
Expand All @@ -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];
Expand Down Expand Up @@ -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];
Expand All @@ -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)
Expand Down Expand Up @@ -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;
Expand All @@ -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);
Expand All @@ -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);
Expand Down Expand Up @@ -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) {
Expand Down Expand Up @@ -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:
Expand All @@ -587,7 +586,7 @@ static ssize_t ib_umad_write(struct file *filp, const char __user *buf,
err_ah:
ib_destroy_ah(ah);
err_up:
up_read(&file->port->mutex);
mutex_unlock(&file->mutex);
err:
kfree(packet);
return ret;
Expand All @@ -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;
Expand Down Expand Up @@ -666,13 +666,13 @@ static int ib_umad_reg_agent(struct ib_umad_file *file, void __user *arg,
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;
}

Expand All @@ -690,7 +690,13 @@ static int ib_umad_reg_agent(struct ib_umad_file *file, void __user *arg,
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;
}

Expand All @@ -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;
Expand All @@ -714,24 +721,26 @@ 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;
}

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;
}
Expand Down Expand Up @@ -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;
Expand All @@ -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);
Expand All @@ -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;
}

Expand All @@ -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;
Expand All @@ -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);
Expand Down Expand Up @@ -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);

Expand Down Expand Up @@ -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();
Expand Down Expand Up @@ -1052,6 +1062,7 @@ static int ib_umad_init_port(struct ib_device *device, int port_num,
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);
Expand All @@ -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);
}
Expand Down

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