Revision 774a1221e862b343388347bac9b318767336b20b authored by Tejun Heo on 16 January 2013, 02:52:51 UTC, committed by Linus Torvalds on 16 January 2013, 17:05:33 UTC
If the default iosched is built as module, the kernel may deadlock while trying to load the iosched module on device probe if the probing was running off async. This is because async_synchronize_full() at the end of module init ends up waiting for the async job which initiated the module loading. async A modprobe 1. finds a device 2. registers the block device 3. request_module(default iosched) 4. modprobe in userland 5. load and init module 6. async_synchronize_full() Async A waits for modprobe to finish in request_module() and modprobe waits for async A to finish in async_synchronize_full(). Because there's no easy to track dependency once control goes out to userland, implementing properly nested flushing is difficult. For now, make module init perform async_synchronize_full() iff module init has queued async jobs as suggested by Linus. This avoids the described deadlock because iosched module doesn't use async and thus wouldn't invoke async_synchronize_full(). This is hacky and incomplete. It will deadlock if async module loading nests; however, this works around the known problem case and seems to be the best of bad options. For more details, please refer to the following thread. http://thread.gmane.org/gmane.linux.kernel/1420814 Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Alex Riesen <raa.lkml@gmail.com> Tested-by: Ming Lei <ming.lei@canonical.com> Tested-by: Alex Riesen <raa.lkml@gmail.com> Cc: Arjan van de Ven <arjan@linux.intel.com> Cc: Jens Axboe <axboe@kernel.dk> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 parent 406089d
threads.c
/*
* Copyright (c) 2006 Oracle. 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
* General Public License (GPL) Version 2, available from the file
* COPYING in the main directory of this source tree, or the
* OpenIB.org BSD license below:
*
* Redistribution and use in source and binary forms, with or
* without modification, are permitted provided that the following
* conditions are met:
*
* - Redistributions of source code must retain the above
* copyright notice, this list of conditions and the following
* disclaimer.
*
* - Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following
* disclaimer in the documentation and/or other materials
* provided with the distribution.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*
*/
#include <linux/kernel.h>
#include <linux/random.h>
#include <linux/export.h>
#include "rds.h"
/*
* All of connection management is simplified by serializing it through
* work queues that execute in a connection managing thread.
*
* TCP wants to send acks through sendpage() in response to data_ready(),
* but it needs a process context to do so.
*
* The receive paths need to allocate but can't drop packets (!) so we have
* a thread around to block allocating if the receive fast path sees an
* allocation failure.
*/
/* Grand Unified Theory of connection life cycle:
* At any point in time, the connection can be in one of these states:
* DOWN, CONNECTING, UP, DISCONNECTING, ERROR
*
* The following transitions are possible:
* ANY -> ERROR
* UP -> DISCONNECTING
* ERROR -> DISCONNECTING
* DISCONNECTING -> DOWN
* DOWN -> CONNECTING
* CONNECTING -> UP
*
* Transition to state DISCONNECTING/DOWN:
* - Inside the shutdown worker; synchronizes with xmit path
* through RDS_IN_XMIT, and with connection management callbacks
* via c_cm_lock.
*
* For receive callbacks, we rely on the underlying transport
* (TCP, IB/RDMA) to provide the necessary synchronisation.
*/
struct workqueue_struct *rds_wq;
EXPORT_SYMBOL_GPL(rds_wq);
void rds_connect_complete(struct rds_connection *conn)
{
if (!rds_conn_transition(conn, RDS_CONN_CONNECTING, RDS_CONN_UP)) {
printk(KERN_WARNING "%s: Cannot transition to state UP, "
"current state is %d\n",
__func__,
atomic_read(&conn->c_state));
atomic_set(&conn->c_state, RDS_CONN_ERROR);
queue_work(rds_wq, &conn->c_down_w);
return;
}
rdsdebug("conn %p for %pI4 to %pI4 complete\n",
conn, &conn->c_laddr, &conn->c_faddr);
conn->c_reconnect_jiffies = 0;
set_bit(0, &conn->c_map_queued);
queue_delayed_work(rds_wq, &conn->c_send_w, 0);
queue_delayed_work(rds_wq, &conn->c_recv_w, 0);
}
EXPORT_SYMBOL_GPL(rds_connect_complete);
/*
* This random exponential backoff is relied on to eventually resolve racing
* connects.
*
* If connect attempts race then both parties drop both connections and come
* here to wait for a random amount of time before trying again. Eventually
* the backoff range will be so much greater than the time it takes to
* establish a connection that one of the pair will establish the connection
* before the other's random delay fires.
*
* Connection attempts that arrive while a connection is already established
* are also considered to be racing connects. This lets a connection from
* a rebooted machine replace an existing stale connection before the transport
* notices that the connection has failed.
*
* We should *always* start with a random backoff; otherwise a broken connection
* will always take several iterations to be re-established.
*/
void rds_queue_reconnect(struct rds_connection *conn)
{
unsigned long rand;
rdsdebug("conn %p for %pI4 to %pI4 reconnect jiffies %lu\n",
conn, &conn->c_laddr, &conn->c_faddr,
conn->c_reconnect_jiffies);
set_bit(RDS_RECONNECT_PENDING, &conn->c_flags);
if (conn->c_reconnect_jiffies == 0) {
conn->c_reconnect_jiffies = rds_sysctl_reconnect_min_jiffies;
queue_delayed_work(rds_wq, &conn->c_conn_w, 0);
return;
}
get_random_bytes(&rand, sizeof(rand));
rdsdebug("%lu delay %lu ceil conn %p for %pI4 -> %pI4\n",
rand % conn->c_reconnect_jiffies, conn->c_reconnect_jiffies,
conn, &conn->c_laddr, &conn->c_faddr);
queue_delayed_work(rds_wq, &conn->c_conn_w,
rand % conn->c_reconnect_jiffies);
conn->c_reconnect_jiffies = min(conn->c_reconnect_jiffies * 2,
rds_sysctl_reconnect_max_jiffies);
}
void rds_connect_worker(struct work_struct *work)
{
struct rds_connection *conn = container_of(work, struct rds_connection, c_conn_w.work);
int ret;
clear_bit(RDS_RECONNECT_PENDING, &conn->c_flags);
if (rds_conn_transition(conn, RDS_CONN_DOWN, RDS_CONN_CONNECTING)) {
ret = conn->c_trans->conn_connect(conn);
rdsdebug("conn %p for %pI4 to %pI4 dispatched, ret %d\n",
conn, &conn->c_laddr, &conn->c_faddr, ret);
if (ret) {
if (rds_conn_transition(conn, RDS_CONN_CONNECTING, RDS_CONN_DOWN))
rds_queue_reconnect(conn);
else
rds_conn_error(conn, "RDS: connect failed\n");
}
}
}
void rds_send_worker(struct work_struct *work)
{
struct rds_connection *conn = container_of(work, struct rds_connection, c_send_w.work);
int ret;
if (rds_conn_state(conn) == RDS_CONN_UP) {
ret = rds_send_xmit(conn);
rdsdebug("conn %p ret %d\n", conn, ret);
switch (ret) {
case -EAGAIN:
rds_stats_inc(s_send_immediate_retry);
queue_delayed_work(rds_wq, &conn->c_send_w, 0);
break;
case -ENOMEM:
rds_stats_inc(s_send_delayed_retry);
queue_delayed_work(rds_wq, &conn->c_send_w, 2);
default:
break;
}
}
}
void rds_recv_worker(struct work_struct *work)
{
struct rds_connection *conn = container_of(work, struct rds_connection, c_recv_w.work);
int ret;
if (rds_conn_state(conn) == RDS_CONN_UP) {
ret = conn->c_trans->recv(conn);
rdsdebug("conn %p ret %d\n", conn, ret);
switch (ret) {
case -EAGAIN:
rds_stats_inc(s_recv_immediate_retry);
queue_delayed_work(rds_wq, &conn->c_recv_w, 0);
break;
case -ENOMEM:
rds_stats_inc(s_recv_delayed_retry);
queue_delayed_work(rds_wq, &conn->c_recv_w, 2);
default:
break;
}
}
}
void rds_shutdown_worker(struct work_struct *work)
{
struct rds_connection *conn = container_of(work, struct rds_connection, c_down_w);
rds_conn_shutdown(conn);
}
void rds_threads_exit(void)
{
destroy_workqueue(rds_wq);
}
int rds_threads_init(void)
{
rds_wq = create_singlethread_workqueue("krdsd");
if (!rds_wq)
return -ENOMEM;
return 0;
}
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