[PATCH v3 2/6] uas: properly reinitialize in uas_eh_bus_reset_handler

[PATCH v3 2/6] uas: properly reinitialize in uas_eh_bus_reset_handler

[Gerd Hoffmann]

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 drivers/usb/storage/uas.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/usb/storage/uas.c b/drivers/usb/storage/uas.c
index d966b59..fc08ee9 100644
--- a/drivers/usb/storage/uas.c
+++ b/drivers/usb/storage/uas.c
@@ -85,6 +85,8 @@ static int uas_submit_urbs(struct scsi_cmnd *cmnd,
 				struct uas_dev_info *devinfo, gfp_t gfp);
 static void uas_do_work(struct work_struct *work);
 static int uas_try_complete(struct scsi_cmnd *cmnd, const char *caller);
+static void uas_configure_endpoints(struct uas_dev_info *devinfo);
+static void uas_free_streams(struct uas_dev_info *devinfo);
 
 static DECLARE_WORK(uas_work, uas_do_work);
 static DEFINE_SPINLOCK(uas_work_lock);
@@ -800,7 +802,10 @@ static int uas_eh_bus_reset_handler(struct scsi_cmnd *cmnd)
 	usb_kill_anchored_urbs(&devinfo->cmd_urbs);
 	usb_kill_anchored_urbs(&devinfo->sense_urbs);
 	usb_kill_anchored_urbs(&devinfo->data_urbs);
+	uas_free_streams(devinfo);
 	err = usb_reset_device(udev);
+	if (!err)
+		uas_configure_endpoints(devinfo);
 	devinfo->resetting = 0;
 
 	if (err) {
-- 
1.8.3.1

[PATCH v3 3/6] uas: make work list per-device

[Gerd Hoffmann]

Simplifies locking, we'll protect the list with the device spin lock.
Also plugs races which can happen when two devices operate on the
global list.

While being at it rename the list head from "list" to "work", preparing
for the addition of a second list.

Signed-off-by: Gerd Hoffmann <kraxel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
---
 drivers/usb/storage/uas.c | 106 +++++++++++++++++++---------------------------
 1 file changed, 44 insertions(+), 62 deletions(-)

diff --git a/drivers/usb/storage/uas.c b/drivers/usb/storage/uas.c
index fc08ee9..3cf5a5f 100644
--- a/drivers/usb/storage/uas.c
+++ b/drivers/usb/storage/uas.c
@@ -51,6 +51,8 @@ struct uas_dev_info {
 	unsigned uas_sense_old:1;
 	struct scsi_cmnd *cmnd;
 	spinlock_t lock;
+	struct work_struct work;
+	struct list_head work_list;
 };
 
 enum {
@@ -77,7 +79,7 @@ struct uas_cmd_info {
 	struct urb *cmd_urb;
 	struct urb *data_in_urb;
 	struct urb *data_out_urb;
-	struct list_head list;
+	struct list_head work;
 };
 
 /* I hate forward declarations, but I actually have a loop */
@@ -88,10 +90,6 @@ static int uas_try_complete(struct scsi_cmnd *cmnd, const char *caller);
 static void uas_configure_endpoints(struct uas_dev_info *devinfo);
 static void uas_free_streams(struct uas_dev_info *devinfo);
 
-static DECLARE_WORK(uas_work, uas_do_work);
-static DEFINE_SPINLOCK(uas_work_lock);
-static LIST_HEAD(uas_work_list);
-
 static void uas_unlink_data_urbs(struct uas_dev_info *devinfo,
 				 struct uas_cmd_info *cmdinfo)
 {
@@ -118,75 +116,66 @@ static void uas_unlink_data_urbs(struct uas_dev_info *devinfo,
 
 static void uas_do_work(struct work_struct *work)
 {
+	struct uas_dev_info *devinfo =
+		container_of(work, struct uas_dev_info, work);
 	struct uas_cmd_info *cmdinfo;
 	struct uas_cmd_info *temp;
-	struct list_head list;
 	unsigned long flags;
 	int err;
 
-	spin_lock_irq(&uas_work_lock);
-	list_replace_init(&uas_work_list, &list);
-	spin_unlock_irq(&uas_work_lock);
-
-	list_for_each_entry_safe(cmdinfo, temp, &list, list) {
+	spin_lock_irqsave(&devinfo->lock, flags);
+	list_for_each_entry_safe(cmdinfo, temp, &devinfo->work_list, work) {
 		struct scsi_pointer *scp = (void *)cmdinfo;
-		struct scsi_cmnd *cmnd = container_of(scp,
-							struct scsi_cmnd, SCp);
-		struct uas_dev_info *devinfo = (void *)cmnd->device->hostdata;
-		spin_lock_irqsave(&devinfo->lock, flags);
+		struct scsi_cmnd *cmnd = container_of(scp, struct scsi_cmnd,
+						      SCp);
 		err = uas_submit_urbs(cmnd, cmnd->device->hostdata, GFP_ATOMIC);
-		if (!err)
+		if (!err) {
 			cmdinfo->state &= ~IS_IN_WORK_LIST;
-		spin_unlock_irqrestore(&devinfo->lock, flags);
-		if (err) {
-			list_del(&cmdinfo->list);
-			spin_lock_irq(&uas_work_lock);
-			list_add_tail(&cmdinfo->list, &uas_work_list);
-			spin_unlock_irq(&uas_work_lock);
-			schedule_work(&uas_work);
+			list_del(&cmdinfo->work);
+		} else {
+			schedule_work(&devinfo->work);
 		}
 	}
+	spin_unlock_irqrestore(&devinfo->lock, flags);
 }
 
 static void uas_abort_work(struct uas_dev_info *devinfo)
 {
 	struct uas_cmd_info *cmdinfo;
 	struct uas_cmd_info *temp;
-	struct list_head list;
 	unsigned long flags;
 
-	spin_lock_irq(&uas_work_lock);
-	list_replace_init(&uas_work_list, &list);
-	spin_unlock_irq(&uas_work_lock);
-
 	spin_lock_irqsave(&devinfo->lock, flags);
-	list_for_each_entry_safe(cmdinfo, temp, &list, list) {
+	list_for_each_entry_safe(cmdinfo, temp, &devinfo->work_list, work) {
 		struct scsi_pointer *scp = (void *)cmdinfo;
-		struct scsi_cmnd *cmnd = container_of(scp,
-							struct scsi_cmnd, SCp);
-		struct uas_dev_info *di = (void *)cmnd->device->hostdata;
-
-		if (di == devinfo) {
-			cmdinfo->state |= COMMAND_ABORTED;
-			cmdinfo->state &= ~IS_IN_WORK_LIST;
-			if (devinfo->resetting) {
-				/* uas_stat_cmplt() will not do that
-				 * when a device reset is in
-				 * progress */
-				cmdinfo->state &= ~COMMAND_INFLIGHT;
-			}
-			uas_try_complete(cmnd, __func__);
-		} else {
-			/* not our uas device, relink into list */
-			list_del(&cmdinfo->list);
-			spin_lock_irq(&uas_work_lock);
-			list_add_tail(&cmdinfo->list, &uas_work_list);
-			spin_unlock_irq(&uas_work_lock);
+		struct scsi_cmnd *cmnd = container_of(scp, struct scsi_cmnd,
+						      SCp);
+		cmdinfo->state |= COMMAND_ABORTED;
+		cmdinfo->state &= ~IS_IN_WORK_LIST;
+		if (devinfo->resetting) {
+			/* uas_stat_cmplt() will not do that
+			 * when a device reset is in
+			 * progress */
+			cmdinfo->state &= ~COMMAND_INFLIGHT;
 		}
+		uas_try_complete(cmnd, __func__);
+		list_del(&cmdinfo->work);
 	}
 	spin_unlock_irqrestore(&devinfo->lock, flags);
 }
 
+static void uas_add_work(struct uas_cmd_info *cmdinfo)
+{
+	struct scsi_pointer *scp = (void *)cmdinfo;
+	struct scsi_cmnd *cmnd = container_of(scp, struct scsi_cmnd, SCp);
+	struct uas_dev_info *devinfo = cmnd->device->hostdata;
+
+	WARN_ON(!spin_is_locked(&devinfo->lock));
+	list_add_tail(&cmdinfo->work, &devinfo->work_list);
+	cmdinfo->state |= IS_IN_WORK_LIST;
+	schedule_work(&devinfo->work);
+}
+
 static void uas_sense(struct urb *urb, struct scsi_cmnd *cmnd)
 {
 	struct sense_iu *sense_iu = urb->transfer_buffer;
@@ -288,11 +277,7 @@ static void uas_xfer_data(struct urb *urb, struct scsi_cmnd *cmnd,
 	cmdinfo->state |= direction | SUBMIT_STATUS_URB;
 	err = uas_submit_urbs(cmnd, cmnd->device->hostdata, GFP_ATOMIC);
 	if (err) {
-		spin_lock(&uas_work_lock);
-		list_add_tail(&cmdinfo->list, &uas_work_list);
-		cmdinfo->state |= IS_IN_WORK_LIST;
-		spin_unlock(&uas_work_lock);
-		schedule_work(&uas_work);
+		uas_add_work(cmdinfo);
 	}
 }
 
@@ -694,11 +679,7 @@ static int uas_queuecommand_lck(struct scsi_cmnd *cmnd,
 			spin_unlock_irqrestore(&devinfo->lock, flags);
 			return SCSI_MLQUEUE_DEVICE_BUSY;
 		}
-		spin_lock(&uas_work_lock);
-		list_add_tail(&cmdinfo->list, &uas_work_list);
-		cmdinfo->state |= IS_IN_WORK_LIST;
-		spin_unlock(&uas_work_lock);
-		schedule_work(&uas_work);
+		uas_add_work(cmdinfo);
 	}
 
 	spin_unlock_irqrestore(&devinfo->lock, flags);
@@ -764,10 +745,8 @@ static int uas_eh_abort_handler(struct scsi_cmnd *cmnd)
 	spin_lock_irqsave(&devinfo->lock, flags);
 	cmdinfo->state |= COMMAND_ABORTED;
 	if (cmdinfo->state & IS_IN_WORK_LIST) {
-		spin_lock(&uas_work_lock);
-		list_del(&cmdinfo->list);
+		list_del(&cmdinfo->work);
 		cmdinfo->state &= ~IS_IN_WORK_LIST;
-		spin_unlock(&uas_work_lock);
 	}
 	if (cmdinfo->state & COMMAND_INFLIGHT) {
 		spin_unlock_irqrestore(&devinfo->lock, flags);
@@ -1007,6 +986,8 @@ static int uas_probe(struct usb_interface *intf, const struct usb_device_id *id)
 	init_usb_anchor(&devinfo->sense_urbs);
 	init_usb_anchor(&devinfo->data_urbs);
 	spin_lock_init(&devinfo->lock);
+	INIT_WORK(&devinfo->work, uas_do_work);
+	INIT_LIST_HEAD(&devinfo->work_list);
 	uas_configure_endpoints(devinfo);
 
 	result = scsi_init_shared_tag_map(shost, devinfo->qdepth - 3);
@@ -1050,6 +1031,7 @@ static void uas_disconnect(struct usb_interface *intf)
 	struct uas_dev_info *devinfo = (void *)shost->hostdata[0];
 
 	devinfo->resetting = 1;
+	cancel_work_sync(&devinfo->work);
 	uas_abort_work(devinfo);
 	usb_kill_anchored_urbs(&devinfo->cmd_urbs);
 	usb_kill_anchored_urbs(&devinfo->sense_urbs);
-- 
1.8.3.1

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[PATCH v3 4/6] uas: add dead request list

[Gerd Hoffmann]

This patch adds a new list where all requests which are canceled are
added to, so we don't loose them.  Then, after killing all inflight
urbs on bus reset (and disconnect) we'll walk over the list and clean
them up.

Without this we can end up with aborted requests lingering around in
case of status pipe transfer errors.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 drivers/usb/storage/uas.c | 50 +++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 42 insertions(+), 8 deletions(-)

diff --git a/drivers/usb/storage/uas.c b/drivers/usb/storage/uas.c
index 3cf5a5f..f049038 100644
--- a/drivers/usb/storage/uas.c
+++ b/drivers/usb/storage/uas.c
@@ -53,6 +53,7 @@ struct uas_dev_info {
 	spinlock_t lock;
 	struct work_struct work;
 	struct list_head work_list;
+	struct list_head dead_list;
 };
 
 enum {
@@ -80,6 +81,7 @@ struct uas_cmd_info {
 	struct urb *data_in_urb;
 	struct urb *data_out_urb;
 	struct list_head work;
+	struct list_head dead;
 };
 
 /* I hate forward declarations, but I actually have a loop */
@@ -89,6 +91,7 @@ static void uas_do_work(struct work_struct *work);
 static int uas_try_complete(struct scsi_cmnd *cmnd, const char *caller);
 static void uas_configure_endpoints(struct uas_dev_info *devinfo);
 static void uas_free_streams(struct uas_dev_info *devinfo);
+static void uas_log_cmd_state(struct scsi_cmnd *cmnd, const char *caller);
 
 static void uas_unlink_data_urbs(struct uas_dev_info *devinfo,
 				 struct uas_cmd_info *cmdinfo)
@@ -150,16 +153,12 @@ static void uas_abort_work(struct uas_dev_info *devinfo)
 		struct scsi_pointer *scp = (void *)cmdinfo;
 		struct scsi_cmnd *cmnd = container_of(scp, struct scsi_cmnd,
 						      SCp);
+		uas_log_cmd_state(cmnd, __func__);
+		WARN_ON(cmdinfo->state & COMMAND_ABORTED);
 		cmdinfo->state |= COMMAND_ABORTED;
 		cmdinfo->state &= ~IS_IN_WORK_LIST;
-		if (devinfo->resetting) {
-			/* uas_stat_cmplt() will not do that
-			 * when a device reset is in
-			 * progress */
-			cmdinfo->state &= ~COMMAND_INFLIGHT;
-		}
-		uas_try_complete(cmnd, __func__);
 		list_del(&cmdinfo->work);
+		list_add_tail(&cmdinfo->dead, &devinfo->dead_list);
 	}
 	spin_unlock_irqrestore(&devinfo->lock, flags);
 }
@@ -176,6 +175,28 @@ static void uas_add_work(struct uas_cmd_info *cmdinfo)
 	schedule_work(&devinfo->work);
 }
 
+static void uas_zap_dead(struct uas_dev_info *devinfo)
+{
+	struct uas_cmd_info *cmdinfo;
+	struct uas_cmd_info *temp;
+	unsigned long flags;
+
+	spin_lock_irqsave(&devinfo->lock, flags);
+	list_for_each_entry_safe(cmdinfo, temp, &devinfo->dead_list, dead) {
+		struct scsi_pointer *scp = (void *)cmdinfo;
+		struct scsi_cmnd *cmnd = container_of(scp, struct scsi_cmnd,
+						      SCp);
+		uas_log_cmd_state(cmnd, __func__);
+		WARN_ON(!(cmdinfo->state & COMMAND_ABORTED));
+		/* all urbs are killed, clear inflight bits */
+		cmdinfo->state &= ~(COMMAND_INFLIGHT |
+				    DATA_IN_URB_INFLIGHT |
+				    DATA_OUT_URB_INFLIGHT);
+		uas_try_complete(cmnd, __func__);
+	}
+	spin_unlock_irqrestore(&devinfo->lock, flags);
+}
+
 static void uas_sense(struct urb *urb, struct scsi_cmnd *cmnd)
 {
 	struct sense_iu *sense_iu = urb->transfer_buffer;
@@ -263,6 +284,7 @@ static int uas_try_complete(struct scsi_cmnd *cmnd, const char *caller)
 	if (cmdinfo->state & COMMAND_ABORTED) {
 		scmd_printk(KERN_INFO, cmnd, "abort completed\n");
 		cmnd->result = DID_ABORT << 16;
+		list_del(&cmdinfo->dead);
 	}
 	cmnd->scsi_done(cmnd);
 	return 0;
@@ -292,7 +314,13 @@ static void uas_stat_cmplt(struct urb *urb)
 	u16 tag;
 
 	if (urb->status) {
-		dev_err(&urb->dev->dev, "URB BAD STATUS %d\n", urb->status);
+		if (urb->status == -ENOENT) {
+			dev_err(&urb->dev->dev, "stat urb: killed, stream %d\n",
+				urb->stream_id);
+		} else {
+			dev_err(&urb->dev->dev, "stat urb: status %d\n",
+				urb->status);
+		}
 		usb_free_urb(urb);
 		return;
 	}
@@ -743,7 +771,9 @@ static int uas_eh_abort_handler(struct scsi_cmnd *cmnd)
 
 	uas_log_cmd_state(cmnd, __func__);
 	spin_lock_irqsave(&devinfo->lock, flags);
+	WARN_ON(cmdinfo->state & COMMAND_ABORTED);
 	cmdinfo->state |= COMMAND_ABORTED;
+	list_add_tail(&cmdinfo->dead, &devinfo->dead_list);
 	if (cmdinfo->state & IS_IN_WORK_LIST) {
 		list_del(&cmdinfo->work);
 		cmdinfo->state &= ~IS_IN_WORK_LIST;
@@ -776,11 +806,13 @@ static int uas_eh_bus_reset_handler(struct scsi_cmnd *cmnd)
 	struct usb_device *udev = devinfo->udev;
 	int err;
 
+	shost_printk(KERN_INFO, sdev->host, "%s start\n", __func__);
 	devinfo->resetting = 1;
 	uas_abort_work(devinfo);
 	usb_kill_anchored_urbs(&devinfo->cmd_urbs);
 	usb_kill_anchored_urbs(&devinfo->sense_urbs);
 	usb_kill_anchored_urbs(&devinfo->data_urbs);
+	uas_zap_dead(devinfo);
 	uas_free_streams(devinfo);
 	err = usb_reset_device(udev);
 	if (!err)
@@ -988,6 +1020,7 @@ static int uas_probe(struct usb_interface *intf, const struct usb_device_id *id)
 	spin_lock_init(&devinfo->lock);
 	INIT_WORK(&devinfo->work, uas_do_work);
 	INIT_LIST_HEAD(&devinfo->work_list);
+	INIT_LIST_HEAD(&devinfo->dead_list);
 	uas_configure_endpoints(devinfo);
 
 	result = scsi_init_shared_tag_map(shost, devinfo->qdepth - 3);
@@ -1036,6 +1069,7 @@ static void uas_disconnect(struct usb_interface *intf)
 	usb_kill_anchored_urbs(&devinfo->cmd_urbs);
 	usb_kill_anchored_urbs(&devinfo->sense_urbs);
 	usb_kill_anchored_urbs(&devinfo->data_urbs);
+	uas_zap_dead(devinfo);
 	scsi_remove_host(shost);
 	uas_free_streams(devinfo);
 	kfree(devinfo);
-- 
1.8.3.1

[PATCH v3 5/6] uas: replace BUG_ON() + WARN_ON() with WARN_ON_ONCE()

[Gerd Hoffmann]

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 drivers/usb/storage/uas.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/drivers/usb/storage/uas.c b/drivers/usb/storage/uas.c
index f049038..046eedf 100644
--- a/drivers/usb/storage/uas.c
+++ b/drivers/usb/storage/uas.c
@@ -154,7 +154,7 @@ static void uas_abort_work(struct uas_dev_info *devinfo)
 		struct scsi_cmnd *cmnd = container_of(scp, struct scsi_cmnd,
 						      SCp);
 		uas_log_cmd_state(cmnd, __func__);
-		WARN_ON(cmdinfo->state & COMMAND_ABORTED);
+		WARN_ON_ONCE(cmdinfo->state & COMMAND_ABORTED);
 		cmdinfo->state |= COMMAND_ABORTED;
 		cmdinfo->state &= ~IS_IN_WORK_LIST;
 		list_del(&cmdinfo->work);
@@ -169,7 +169,7 @@ static void uas_add_work(struct uas_cmd_info *cmdinfo)
 	struct scsi_cmnd *cmnd = container_of(scp, struct scsi_cmnd, SCp);
 	struct uas_dev_info *devinfo = cmnd->device->hostdata;
 
-	WARN_ON(!spin_is_locked(&devinfo->lock));
+	WARN_ON_ONCE(!spin_is_locked(&devinfo->lock));
 	list_add_tail(&cmdinfo->work, &devinfo->work_list);
 	cmdinfo->state |= IS_IN_WORK_LIST;
 	schedule_work(&devinfo->work);
@@ -187,7 +187,7 @@ static void uas_zap_dead(struct uas_dev_info *devinfo)
 		struct scsi_cmnd *cmnd = container_of(scp, struct scsi_cmnd,
 						      SCp);
 		uas_log_cmd_state(cmnd, __func__);
-		WARN_ON(!(cmdinfo->state & COMMAND_ABORTED));
+		WARN_ON_ONCE(!(cmdinfo->state & COMMAND_ABORTED));
 		/* all urbs are killed, clear inflight bits */
 		cmdinfo->state &= ~(COMMAND_INFLIGHT |
 				    DATA_IN_URB_INFLIGHT |
@@ -271,13 +271,13 @@ static int uas_try_complete(struct scsi_cmnd *cmnd, const char *caller)
 	struct uas_cmd_info *cmdinfo = (void *)&cmnd->SCp;
 	struct uas_dev_info *devinfo = (void *)cmnd->device->hostdata;
 
-	WARN_ON(!spin_is_locked(&devinfo->lock));
+	WARN_ON_ONCE(!spin_is_locked(&devinfo->lock));
 	if (cmdinfo->state & (COMMAND_INFLIGHT |
 			      DATA_IN_URB_INFLIGHT |
 			      DATA_OUT_URB_INFLIGHT |
 			      UNLINK_DATA_URBS))
 		return -EBUSY;
-	BUG_ON(cmdinfo->state & COMMAND_COMPLETED);
+	WARN_ON_ONCE(cmdinfo->state & COMMAND_COMPLETED);
 	cmdinfo->state |= COMMAND_COMPLETED;
 	usb_free_urb(cmdinfo->data_in_urb);
 	usb_free_urb(cmdinfo->data_out_urb);
@@ -398,8 +398,9 @@ static void uas_data_cmplt(struct urb *urb)
 		sdb = scsi_out(cmnd);
 		cmdinfo->state &= ~DATA_OUT_URB_INFLIGHT;
 	}
-	BUG_ON(sdb == NULL);
-	if (urb->status) {
+	if (sdb == NULL) {
+		WARN_ON_ONCE(1);
+	} else if (urb->status) {
 		/* error: no data transfered */
 		sdb->resid = sdb->length;
 	} else {
@@ -573,7 +574,7 @@ static int uas_submit_urbs(struct scsi_cmnd *cmnd,
 	struct uas_cmd_info *cmdinfo = (void *)&cmnd->SCp;
 	int err;
 
-	WARN_ON(!spin_is_locked(&devinfo->lock));
+	WARN_ON_ONCE(!spin_is_locked(&devinfo->lock));
 	if (cmdinfo->state & SUBMIT_STATUS_URB) {
 		err = uas_submit_sense_urb(cmnd->device->host, gfp,
 					   cmdinfo->stream);
@@ -771,7 +772,7 @@ static int uas_eh_abort_handler(struct scsi_cmnd *cmnd)
 
 	uas_log_cmd_state(cmnd, __func__);
 	spin_lock_irqsave(&devinfo->lock, flags);
-	WARN_ON(cmdinfo->state & COMMAND_ABORTED);
+	WARN_ON_ONCE(cmdinfo->state & COMMAND_ABORTED);
 	cmdinfo->state |= COMMAND_ABORTED;
 	list_add_tail(&cmdinfo->dead, &devinfo->dead_list);
 	if (cmdinfo->state & IS_IN_WORK_LIST) {
-- 
1.8.3.1

Re: [PATCH v3 3/6] uas: make work list per-device

[Christoph Hellwig]

On Fri, Sep 13, 2013 at 01:27:12PM +0200, Gerd Hoffmann wrote:
> Simplifies locking, we'll protect the list with the device spin lock.
> Also plugs races which can happen when two devices operate on the
> global list.
> 
> While being at it rename the list head from "list" to "work", preparing
> for the addition of a second list.

Why do you even the list?  What would a ordered per-device workqueue not
provide?

Re: [PATCH v3 3/6] uas: make work list per-device

[Gerd Hoffmann]

On Di, 2013-09-17 at 13:30 -0700, Christoph Hellwig wrote:
> On Fri, Sep 13, 2013 at 01:27:12PM +0200, Gerd Hoffmann wrote:
> > Simplifies locking, we'll protect the list with the device spin lock.
> > Also plugs races which can happen when two devices operate on the
> > global list.
> > 
> > While being at it rename the list head from "list" to "work", preparing
> > for the addition of a second list.
> 
> Why do you even the list?

The list was already there when I took over maintainance ...

> What would a ordered per-device workqueue not
> provide?

Had no reason to look into replacing the list with something else so
far.  Why do you suggest using a workqueue instead?

Note that the list is not used in a typical request workflow.  Only in
case queuing an usb urb failed the request is linked into the list and
the worker will try to submit the usb urb again.

cheers,
  Gerd

Re: [PATCH v3 3/6] uas: make work list per-device

[Christoph Hellwig]

On Wed, Sep 18, 2013 at 09:33:04AM +0200, Gerd Hoffmann wrote:
> > > While being at it rename the list head from "list" to "work", preparing
> > > for the addition of a second list.
> > 
> > Why do you even the list?
> 
> The list was already there when I took over maintainance ...
> 
> > What would a ordered per-device workqueue not
> > provide?
> 
> Had no reason to look into replacing the list with something else so
> far.  Why do you suggest using a workqueue instead?
> 
> Note that the list is not used in a typical request workflow.  Only in
> case queuing an usb urb failed the request is linked into the list and
> the worker will try to submit the usb urb again.

The driver is only using the list to queue up things into workqueue
context as far as I can see.  Which means it's far easier to leave that
to the workqueue.