UAS: fix deadlock in error handling and PM flushing work

A SCSI error handler and block runtime PM must not allocate
memory with GFP_KERNEL. Furthermore they must not wait for
tasks allocating memory with GFP_KERNEL.
That means that they cannot share a workqueue with arbitrary tasks.

Fix this for UAS using a private workqueue.

Signed-off-by: Oliver Neukum <oneukum@suse.com>
Fixes: f9dc024a2da1f ("uas: pre_reset and suspend: Fix a few races")
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20200415141750.811-2-oneukum@suse.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/storage/uas.c b/drivers/usb/storage/uas.c
index 08503e3..d592071 100644 (file)
--- a/drivers/usb/storage/uas.c
+++ b/drivers/usb/storage/uas.c
@@ -81,6 +81,19 @@ static void uas_free_streams(struct uas_dev_info *devinfo);
 static void uas_log_cmd_state(struct scsi_cmnd *cmnd, const char *prefix,
                                int status);
 
+/*
+ * This driver needs its own workqueue, as we need to control memory allocation.
+ *
+ * In the course of error handling and power management uas_wait_for_pending_cmnds()
+ * needs to flush pending work items. In these contexts we cannot allocate memory
+ * by doing block IO as we would deadlock. For the same reason we cannot wait
+ * for anything allocating memory not heeding these constraints.
+ *
+ * So we have to control all work items that can be on the workqueue we flush.
+ * Hence we cannot share a queue and need our own.
+ */
+static struct workqueue_struct *workqueue;
+
 static void uas_do_work(struct work_struct *work)
 {
        struct uas_dev_info *devinfo =
@@ -109,7 +122,7 @@ static void uas_do_work(struct work_struct *work)
                if (!err)
                        cmdinfo->state &= ~IS_IN_WORK_LIST;
                else
-                       schedule_work(&devinfo->work);
+                       queue_work(workqueue, &devinfo->work);
        }
 out:
        spin_unlock_irqrestore(&devinfo->lock, flags);
@@ -134,7 +147,7 @@ static void uas_add_work(struct uas_cmd_info *cmdinfo)
 
        lockdep_assert_held(&devinfo->lock);
        cmdinfo->state |= IS_IN_WORK_LIST;
-       schedule_work(&devinfo->work);
+       queue_work(workqueue, &devinfo->work);
 }
 
 static void uas_zap_pending(struct uas_dev_info *devinfo, int result)
@@ -1229,7 +1242,31 @@ static struct usb_driver uas_driver = {
        .id_table = uas_usb_ids,
 };
 
-module_usb_driver(uas_driver);
+static int __init uas_init(void)
+{
+       int rv;
+
+       workqueue = alloc_workqueue("uas", WQ_MEM_RECLAIM, 0);
+       if (!workqueue)
+               return -ENOMEM;
+
+       rv = usb_register(&uas_driver);
+       if (rv) {
+               destroy_workqueue(workqueue);
+               return -ENOMEM;
+       }
+
+       return 0;
+}
+
+static void __exit uas_exit(void)
+{
+       usb_deregister(&uas_driver);
+       destroy_workqueue(workqueue);
+}
+
+module_init(uas_init);
+module_exit(uas_exit);
 
 MODULE_LICENSE("GPL");
 MODULE_IMPORT_NS(USB_STORAGE);