[PATCH 07/19] tcmu: fix unmap thread race

[Mike Christie]

If the unmap thread has already run find_free_blocks
but not yet run prepare_to_wait when a wake_up(&unmap_wait)
call is done, the unmap thread is going to miss the wake
call. Instead of adding checks for if new waiters were added
this just has use a work queue which will run us again
in this type of case.

Signed-off-by: Mike Christie <mchri...@redhat.com>
---
 drivers/target/target_core_user.c | 43 +++++++++------------------------------
 1 file changed, 10 insertions(+), 33 deletions(-)

diff --git a/drivers/target/target_core_user.c 
b/drivers/target/target_core_user.c
index 15b54fd..14d9b79 100644
--- a/drivers/target/target_core_user.c
+++ b/drivers/target/target_core_user.c
@@ -32,7 +32,7 @@
 #include <linux/highmem.h>
 #include <linux/configfs.h>
 #include <linux/mutex.h>
-#include <linux/kthread.h>
+#include <linux/workqueue.h>
 #include <net/genetlink.h>
 #include <scsi/scsi_common.h>
 #include <scsi/scsi_proto.h>
@@ -176,12 +176,11 @@ struct tcmu_cmd {
        unsigned long flags;
 };
 
-static struct task_struct *unmap_thread;
-static wait_queue_head_t unmap_wait;
 static DEFINE_MUTEX(root_udev_mutex);
 static LIST_HEAD(root_udev);
 
 static atomic_t global_db_count = ATOMIC_INIT(0);
+static struct work_struct tcmu_unmap_work;
 
 static struct kmem_cache *tcmu_cmd_cache;
 
@@ -389,8 +388,7 @@ static bool tcmu_get_empty_blocks(struct tcmu_dev *udev,
 
 err:
        udev->waiting_global = true;
-       /* Try to wake up the unmap thread */
-       wake_up(&unmap_wait);
+       schedule_work(&tcmu_unmap_work);
        return false;
 }
 
@@ -1063,8 +1061,7 @@ static void tcmu_device_timedout(unsigned long data)
        idr_for_each(&udev->commands, tcmu_check_expired_cmd, NULL);
        spin_unlock_irqrestore(&udev->commands_lock, flags);
 
-       /* Try to wake up the ummap thread */
-       wake_up(&unmap_wait);
+       schedule_work(&tcmu_unmap_work);
 
        /*
         * We don't need to wakeup threads on wait_cmdr since they have their
@@ -2042,23 +2039,10 @@ static void run_cmdr_queues(void)
        mutex_unlock(&root_udev_mutex);
 }
 
-static int unmap_thread_fn(void *data)
+static void tcmu_unmap_work_fn(struct work_struct *work)
 {
-       while (!kthread_should_stop()) {
-               DEFINE_WAIT(__wait);
-
-               prepare_to_wait(&unmap_wait, &__wait, TASK_INTERRUPTIBLE);
-               schedule();
-               finish_wait(&unmap_wait, &__wait);
-
-               if (kthread_should_stop())
-                       break;
-
-               find_free_blocks();
-               run_cmdr_queues();
-       }
-
-       return 0;
+       find_free_blocks();
+       run_cmdr_queues();
 }
 
 static int __init tcmu_module_init(void)
@@ -2067,6 +2051,8 @@ static int __init tcmu_module_init(void)
 
        BUILD_BUG_ON((sizeof(struct tcmu_cmd_entry) % TCMU_OP_ALIGN_SIZE) != 0);
 
+       INIT_WORK(&tcmu_unmap_work, tcmu_unmap_work_fn);
+
        tcmu_cmd_cache = kmem_cache_create("tcmu_cmd_cache",
                                sizeof(struct tcmu_cmd),
                                __alignof__(struct tcmu_cmd),
@@ -2112,17 +2098,8 @@ static int __init tcmu_module_init(void)
        if (ret)
                goto out_attrs;
 
-       init_waitqueue_head(&unmap_wait);
-       unmap_thread = kthread_run(unmap_thread_fn, NULL, "tcmu_unmap");
-       if (IS_ERR(unmap_thread)) {
-               ret = PTR_ERR(unmap_thread);
-               goto out_unreg_transport;
-       }
-
        return 0;
 
-out_unreg_transport:
-       target_backend_unregister(&tcmu_ops);
 out_attrs:
        kfree(tcmu_attrs);
 out_unreg_genl:
@@ -2137,7 +2114,7 @@ static int __init tcmu_module_init(void)
 
 static void __exit tcmu_module_exit(void)
 {
-       kthread_stop(unmap_thread);
+       cancel_work_sync(&tcmu_unmap_work);
        target_backend_unregister(&tcmu_ops);
        kfree(tcmu_attrs);
        genl_unregister_family(&tcmu_genl_family);
-- 
1.8.3.1