From dcc909d90ccdbb73226397ff6d298f7af35b0e11 Mon Sep 17 00:00:00 2001 From: Markus Pargmann Date: Tue, 6 Oct 2015 20:03:54 +0200 Subject: [PATCH] nbd: Add locking for tasks The timeout handling introduced in 7e2893a16d3e (nbd: Fix timeout detection) introduces a race condition which may lead to killing of tasks that are not in nbd context anymore. This was not observed or reproducable yet. This patch adds locking to critical use of task_recv and task_send to avoid killing tasks that already left the NBD thread functions. This lock is only acquired if a timeout occures or the nbd device starts/stops. Reported-by: Ben Hutchings Signed-off-by: Markus Pargmann Reviewed-by: Ben Hutchings Fixes: 7e2893a16d3e ("nbd: Fix timeout detection") Signed-off-by: Jens Axboe --- drivers/block/nbd.c | 36 ++++++++++++++++++++++++++++++------ 1 file changed, 30 insertions(+), 6 deletions(-) diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c index 293495a75d3d..1b87623381e2 100644 --- a/drivers/block/nbd.c +++ b/drivers/block/nbd.c @@ -60,6 +60,7 @@ struct nbd_device { bool disconnect; /* a disconnect has been requested by user */ struct timer_list timeout_timer; + spinlock_t tasks_lock; struct task_struct *task_recv; struct task_struct *task_send; @@ -140,21 +141,23 @@ static void sock_shutdown(struct nbd_device *nbd) static void nbd_xmit_timeout(unsigned long arg) { struct nbd_device *nbd = (struct nbd_device *)arg; - struct task_struct *task; + unsigned long flags; if (list_empty(&nbd->queue_head)) return; nbd->disconnect = true; - task = READ_ONCE(nbd->task_recv); - if (task) - force_sig(SIGKILL, task); + spin_lock_irqsave(&nbd->tasks_lock, flags); - task = READ_ONCE(nbd->task_send); - if (task) + if (nbd->task_recv) + force_sig(SIGKILL, nbd->task_recv); + + if (nbd->task_send) force_sig(SIGKILL, nbd->task_send); + spin_unlock_irqrestore(&nbd->tasks_lock, flags); + dev_err(nbd_to_dev(nbd), "Connection timed out, killed receiver and sender, shutting down connection\n"); } @@ -403,17 +406,24 @@ static int nbd_thread_recv(struct nbd_device *nbd) { struct request *req; int ret; + unsigned long flags; BUG_ON(nbd->magic != NBD_MAGIC); sk_set_memalloc(nbd->sock->sk); + spin_lock_irqsave(&nbd->tasks_lock, flags); nbd->task_recv = current; + spin_unlock_irqrestore(&nbd->tasks_lock, flags); ret = device_create_file(disk_to_dev(nbd->disk), &pid_attr); if (ret) { dev_err(disk_to_dev(nbd->disk), "device_create_file failed!\n"); + + spin_lock_irqsave(&nbd->tasks_lock, flags); nbd->task_recv = NULL; + spin_unlock_irqrestore(&nbd->tasks_lock, flags); + return ret; } @@ -429,7 +439,9 @@ static int nbd_thread_recv(struct nbd_device *nbd) device_remove_file(disk_to_dev(nbd->disk), &pid_attr); + spin_lock_irqsave(&nbd->tasks_lock, flags); nbd->task_recv = NULL; + spin_unlock_irqrestore(&nbd->tasks_lock, flags); if (signal_pending(current)) { siginfo_t info; @@ -534,8 +546,11 @@ static int nbd_thread_send(void *data) { struct nbd_device *nbd = data; struct request *req; + unsigned long flags; + spin_lock_irqsave(&nbd->tasks_lock, flags); nbd->task_send = current; + spin_unlock_irqrestore(&nbd->tasks_lock, flags); set_user_nice(current, MIN_NICE); while (!kthread_should_stop() || !list_empty(&nbd->waiting_queue)) { @@ -572,7 +587,15 @@ static int nbd_thread_send(void *data) nbd_handle_req(nbd, req); } + spin_lock_irqsave(&nbd->tasks_lock, flags); nbd->task_send = NULL; + spin_unlock_irqrestore(&nbd->tasks_lock, flags); + + /* Clear maybe pending signals */ + if (signal_pending(current)) { + siginfo_t info; + dequeue_signal_lock(current, ¤t->blocked, &info); + } return 0; } @@ -1052,6 +1075,7 @@ static int __init nbd_init(void) nbd_dev[i].magic = NBD_MAGIC; INIT_LIST_HEAD(&nbd_dev[i].waiting_queue); spin_lock_init(&nbd_dev[i].queue_lock); + spin_lock_init(&nbd_dev[i].tasks_lock); INIT_LIST_HEAD(&nbd_dev[i].queue_head); mutex_init(&nbd_dev[i].tx_lock); init_timer(&nbd_dev[i].timeout_timer);