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[IB] umad: further ib_unregister_mad_agent() deadlock fixes

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The previous umad deadlock fix left ib_umad_kill_port() still
vulnerable to deadlocking.  This patch fixes that by downgrading our
lock to a read lock when we might end up trying to reacquire the lock
for reading.

Signed-off-by: Roland Dreier <rolandd@cisco.com>
This commit is contained in:
Roland Dreier 2005-11-10 10:18:23 -08:00
parent ae57e24a40
commit 94382f3562
1 changed files with 63 additions and 24 deletions
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87
drivers/infiniband/core/user_mad.c
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@ -31,7 +31,7 @@
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*
* $Id: user_mad.c 2814 2005-07-06 19:14:09Z halr $
* $Id: user_mad.c 4010 2005-11-09 23:11:56Z roland $
*/
#include <linux/module.h>
@ -110,12 +110,13 @@ struct ib_umad_device {
};
struct ib_umad_file {
struct ib_umad_port *port;
struct list_head recv_list;
struct list_head port_list;
spinlock_t recv_lock;
wait_queue_head_t recv_wait;
struct ib_mad_agent *agent[IB_UMAD_MAX_AGENTS];
struct ib_umad_port *port;
struct list_head recv_list;
struct list_head port_list;
spinlock_t recv_lock;
wait_queue_head_t recv_wait;
struct ib_mad_agent *agent[IB_UMAD_MAX_AGENTS];
int agents_dead;
};
struct ib_umad_packet {
@ -144,6 +145,12 @@ static void ib_umad_release_dev(struct kref *ref)
kfree(dev);
}
/* caller must hold port->mutex at least for reading */
static struct ib_mad_agent *__get_agent(struct ib_umad_file *file, int id)
{
return file->agents_dead ? NULL : file->agent[id];
}
static int queue_packet(struct ib_umad_file *file,
struct ib_mad_agent *agent,
struct ib_umad_packet *packet)
@ -151,10 +158,11 @@ static int queue_packet(struct ib_umad_file *file,
int ret = 1;
down_read(&file->port->mutex);
for (packet->mad.hdr.id = 0;
packet->mad.hdr.id < IB_UMAD_MAX_AGENTS;
packet->mad.hdr.id++)
if (agent == file->agent[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);
@ -326,7 +334,7 @@ static ssize_t ib_umad_write(struct file *filp, const char __user *buf,
down_read(&file->port->mutex);
agent = file->agent[packet->mad.hdr.id];
agent = __get_agent(file, packet->mad.hdr.id);
if (!agent) {
ret = -EINVAL;
goto err_up;
@ -480,7 +488,7 @@ static int ib_umad_reg_agent(struct ib_umad_file *file, unsigned long arg)
}
for (agent_id = 0; agent_id < IB_UMAD_MAX_AGENTS; ++agent_id)
if (!file->agent[agent_id])
if (!__get_agent(file, agent_id))
goto found;
ret = -ENOMEM;
@ -530,7 +538,7 @@ static int ib_umad_unreg_agent(struct ib_umad_file *file, unsigned long arg)
down_write(&file->port->mutex);
if (id < 0 || id >= IB_UMAD_MAX_AGENTS || !file->agent[id]) {
if (id < 0 || id >= IB_UMAD_MAX_AGENTS || !__get_agent(file, id)) {
ret = -EINVAL;
goto out;
}
@ -608,21 +616,29 @@ static int ib_umad_close(struct inode *inode, struct file *filp)
struct ib_umad_file *file = filp->private_data;
struct ib_umad_device *dev = file->port->umad_dev;
struct ib_umad_packet *packet, *tmp;
int already_dead;
int i;
for (i = 0; i < IB_UMAD_MAX_AGENTS; ++i)
if (file->agent[i])
ib_unregister_mad_agent(file->agent[i]);
down_write(&file->port->mutex);
already_dead = file->agents_dead;
file->agents_dead = 1;
list_for_each_entry_safe(packet, tmp, &file->recv_list, list)
kfree(packet);
down_write(&file->port->mutex);
list_del(&file->port_list);
up_write(&file->port->mutex);
downgrade_write(&file->port->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);
kfree(file);
kref_put(&dev->ref, ib_umad_release_dev);
return 0;
@ -848,13 +864,36 @@ static void ib_umad_kill_port(struct ib_umad_port *port)
port->ib_dev = NULL;
list_for_each_entry(file, &port->file_list, port_list)
for (id = 0; id < IB_UMAD_MAX_AGENTS; ++id) {
if (!file->agent[id])
continue;
ib_unregister_mad_agent(file->agent[id]);
file->agent[id] = 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);
file->agents_dead = 1;
list_del_init(&file->port_list);
downgrade_write(&port->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);