[PATCH 15/21] uas: pre_reset and suspend: Fix a few races

Hans de Goede
2014-09-10T11:46:45Z

The purpose of uas_pre_reset is to:

1) Stop any new commands from being submitted while an externally triggered
usb-device-reset is running
2) Wait for any pending commands to finish before allowing the usb-device-reset
to continue

The purpose of uas_suspend is to:
2) Wait for any pending commands to finish before suspending

This commit fixes races in both paths:

1) For 1) we use scsi_block_requests, but the scsi midlayer calls queuecommand
without holding any locks, so a queuecommand may already past the midlayer
scsi_block_requests checks when we call it, add a check to uas_queuecommand
to fix this

2) For 2) we were waiting for all sense-urbs to complete, there are 2 problems
with this approach:
a) data-urbs may complete after the sense urb, so we need to check for those
too
b) if a sense-urb completes with a iu id of READ/WRITE_READY a command is not
yet done. We submit a new sense-urb immediately in this case, but that
submit may fail (in which case it will get retried by uas_do_work), if this
happens the sense_urbs anchor may become empty while the cmnd is not yet
done

Also unblock requests on timeout, to avoid things getting stuck in that case.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
drivers/usb/storage/uas.c | 61 ++++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 55 insertions(+), 6 deletions(-)

diff --git a/drivers/usb/storage/uas.c b/drivers/usb/storage/uas.c
index 6ee61bd..aaca65b 100644
--- a/drivers/usb/storage/uas.c
+++ b/drivers/usb/storage/uas.c
@@ -664,6 +664,10 @@ static int uas_queuecommand_lck(struct scsi_cmnd *cmnd,

BUILD_BUG_ON(sizeof(struct uas_cmd_info) > sizeof(struct scsi_pointer));

+ /* Re-check scsi_block_requests now that we've the host-lock */
+ if (cmnd->device->host->host_self_blocked)
+ return SCSI_MLQUEUE_DEVICE_BUSY;
+
spin_lock_irqsave(&devinfo->lock, flags);

if (devinfo->resetting) {
@@ -991,6 +995,54 @@ set_alt0:
return result;
}

+static int uas_cmnd_list_empty(struct uas_dev_info *devinfo)
+{
+ unsigned long flags;
+ int i, r = 1;
+
+ spin_lock_irqsave(&devinfo->lock, flags);
+
+ for (i = 0; i < devinfo->qdepth; i++) {
+ if (devinfo->cmnd[i]) {
+ r = 0; /* Not empty */
+ break;
+ }
+ }
+
+ spin_unlock_irqrestore(&devinfo->lock, flags);
+
+ return r;
+}
+
+/*
+ * Wait for any pending cmnds to complete, on usb-2 sense_urbs may temporarily
+ * get empty while there still is more work to do due to sense-urbs completing
+ * with a READ/WRITE_READY iu code, so keep waiting until the list gets empty.
+ */
+static int uas_wait_for_pending_cmnds(struct uas_dev_info *devinfo)
+{
+ unsigned long start_time;
+ int r;
+
+ start_time = jiffies;
+ do {
+ flush_work(&devinfo->work);
+
+ r = usb_wait_anchor_empty_timeout(&devinfo->sense_urbs, 5000);
+ if (r == 0)
+ return -ETIME;
+
+ r = usb_wait_anchor_empty_timeout(&devinfo->data_urbs, 500);
+ if (r == 0)
+ return -ETIME;
+
+ if (time_after(jiffies, start_time + 5 * HZ))
+ return -ETIME;
+ } while (!uas_cmnd_list_empty(devinfo));
+
+ return 0;
+}
+
static int uas_pre_reset(struct usb_interface *intf)
{
struct Scsi_Host *shost = usb_get_intfdata(intf);
@@ -1005,10 +1057,9 @@ static int uas_pre_reset(struct usb_interface *intf)
scsi_block_requests(shost);
spin_unlock_irqrestore(shost->host_lock, flags);

- /* Wait for any pending requests to complete */
- flush_work(&devinfo->work);
- if (usb_wait_anchor_empty_timeout(&devinfo->sense_urbs, 5000) == 0) {
+ if (uas_wait_for_pending_cmnds(devinfo) != 0) {
shost_printk(KERN_ERR, shost, "%s: timed out\n", __func__);
+ scsi_unblock_requests(shost);
return 1;
}

@@ -1046,9 +1097,7 @@ static int uas_suspend(struct usb_interface *intf, pm_message_t message)
struct Scsi_Host *shost = usb_get_intfdata(intf);
struct uas_dev_info *devinfo = (struct uas_dev_info *)shost->hostdata;

- /* Wait for any pending requests to complete */
- flush_work(&devinfo->work);
- if (usb_wait_anchor_empty_timeout(&devinfo->sense_urbs, 5000) == 0) {
+ if (uas_wait_for_pending_cmnds(devinfo) != 0) {
shost_printk(KERN_ERR, shost, "%s: timed out\n", __func__);
return -ETIME;
}
--
2.1.0