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SubjectRe: [PATCH v2] usb: dwc2: host: Don't retry NAKed transactions right away
Hi,

On Sat, Oct 28, 2017 at 8:51 AM, Stefan Wahren <stefan.wahren@i2se.com> wrote:
> Hi Doug,
>
> [add Felipe since this should go through his tree]

Ah. Sorry Felipe! I know you've landed some dwc2 stuff in the past
but for some reason get_maintainer didn't ID you so I thought maybe
you weren't doing it anymore. Please let me know if you'd like me to
send this to you again with collected Reviewed-by and Tested-by tags.


> i'm back from vacation and happy to see this patch.
>
>> Douglas Anderson <dianders@chromium.org> hat am 26. Oktober 2017 um 22:22 geschrieben:
>>
>>
>> On rk3288-veyron devices on Chrome OS it was found that plugging in an
>> Arduino-based USB device could cause the system to lockup, especially
>> if the CPU Frequency was at one of the slower operating points (like
>> 100 MHz / 200 MHz).
>>
>> Upon tracing, I found that the following was happening:
>> * The USB device (full speed) was connected to a high speed hub and
>> then to the rk3288. Thus, we were dealing with split transactions,
>> which is all handled in software on dwc2.
>> * Userspace was initiating a BULK IN transfer
>> * When we sent the SSPLIT (to start the split transaction), we got an
>> ACK. Good. Then we issued the CSPLIT.
>> * When we sent the CSPLIT, we got back a NAK. We immediately (from
>> the interrupt handler) started to retry and sent another SSPLIT.
>> * The device kept NAKing our CSPLIT, so we kept ping-ponging between
>> sending a SSPLIT and a CSPLIT, each time sending from the interrupt
>> handler.
>> * The handling of the interrupts was (because of the low CPU speed and
>> the inefficiency of the dwc2 interrupt handler) was actually taking
>> _longer_ than it took the other side to send the ACK/NAK. Thus we
>> were _always_ in the USB interrupt routine.
>> * The fact that USB interrupts were always going off was preventing
>> other things from happening in the system. This included preventing
>> the system from being able to transition to a higher CPU frequency.
>>
>> As I understand it, there is no requirement to retry super quickly
>> after a NAK, we just have to retry sometime in the future. Thus one
>> solution to the above is to just add a delay between getting a NAK and
>> retrying the transmission. If this delay is sufficiently long to get
>> out of the interrupt routine then the rest of the system will be able
>> to make forward progress. Even a 25 us delay would probably be
>> enough, but we'll be extra conservative and try to delay 1 ms (the
>> exact amount depends on HZ and the accuracy of the jiffy and how close
>> the current jiffy is to ticking, but could be as much as 20 ms or as
>> little as 1 ms).
>>
>> Presumably adding a delay like this could impact the USB throughput,
>> so we only add the delay with repeated NAKs.
>>
>> NOTE: Upon further testing of a pl2303 serial adapter, I found that
>> this fix may help with problems there. Specifically I found that the
>> pl2303 serial adapters tend to respond with a NAK when they have
>> nothing to say and thus we end with this same sequence.
>
> This patch fixes "dwc2: NMI watchdog: BUG: soft lockup - CPU#0 stuck for 146s" on bcm2835. After applying your patch on linux-next plus "mm: drop migrate type checks from has_unmovable_pages" i'm able to open 3 PL2303 serial adapters parallel on a Raspberry Pi 1 B without any issues.

Woohoo! It only took a year from your report of this issue to getting
a fix. ;) It sounds as if Julius found something the other day too
(dealing better with stalls), so any day now we'll have a mainline
kernel that can keep up with "blazingly fast" UART connections. :-P


> Tested-by: Stefan Wahren <stefan.wahren@i2se.com>


Thank you so much for the testing!


> Please see my comment below
>
>>
>> Signed-off-by: Douglas Anderson <dianders@chromium.org>
>> Reviewed-by: Julius Werner <jwerner@chromium.org>
>> ---
>>
>> Changes in v2:
>> - Address http://crosreview.com/737520 feedback
>>
>> drivers/usb/dwc2/core.h | 1 +
>> drivers/usb/dwc2/hcd.c | 7 ++++
>> drivers/usb/dwc2/hcd.h | 9 +++++
>> drivers/usb/dwc2/hcd_intr.c | 20 +++++++++++
>> drivers/usb/dwc2/hcd_queue.c | 81 +++++++++++++++++++++++++++++++++++++++++---
>> 5 files changed, 114 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/usb/dwc2/core.h b/drivers/usb/dwc2/core.h
>> index 8367d4f985c1..c0807e558726 100644
>> --- a/drivers/usb/dwc2/core.h
>> +++ b/drivers/usb/dwc2/core.h
>> @@ -962,6 +962,7 @@ struct dwc2_hsotg {
>> } flags;
>>
>> struct list_head non_periodic_sched_inactive;
>> + struct list_head non_periodic_sched_waiting;
>> struct list_head non_periodic_sched_active;
>> struct list_head *non_periodic_qh_ptr;
>> struct list_head periodic_sched_inactive;
>> diff --git a/drivers/usb/dwc2/hcd.c b/drivers/usb/dwc2/hcd.c
>> index c2631145f404..ed92ae78dcf9 100644
>> --- a/drivers/usb/dwc2/hcd.c
>> +++ b/drivers/usb/dwc2/hcd.c
>> @@ -653,6 +653,10 @@ static void dwc2_dump_channel_info(struct dwc2_hsotg *hsotg,
>> list_for_each_entry(qh, &hsotg->non_periodic_sched_inactive,
>> qh_list_entry)
>> dev_dbg(hsotg->dev, " %p\n", qh);
>> + dev_dbg(hsotg->dev, " NP waiting sched:\n");
>> + list_for_each_entry(qh, &hsotg->non_periodic_sched_waiting,
>> + qh_list_entry)
>> + dev_dbg(hsotg->dev, " %p\n", qh);
>> dev_dbg(hsotg->dev, " NP active sched:\n");
>> list_for_each_entry(qh, &hsotg->non_periodic_sched_active,
>> qh_list_entry)
>> @@ -1812,6 +1816,7 @@ static void dwc2_qh_list_free(struct dwc2_hsotg *hsotg,
>> static void dwc2_kill_all_urbs(struct dwc2_hsotg *hsotg)
>> {
>> dwc2_kill_urbs_in_qh_list(hsotg, &hsotg->non_periodic_sched_inactive);
>> + dwc2_kill_urbs_in_qh_list(hsotg, &hsotg->non_periodic_sched_waiting);
>> dwc2_kill_urbs_in_qh_list(hsotg, &hsotg->non_periodic_sched_active);
>> dwc2_kill_urbs_in_qh_list(hsotg, &hsotg->periodic_sched_inactive);
>> dwc2_kill_urbs_in_qh_list(hsotg, &hsotg->periodic_sched_ready);
>> @@ -4989,6 +4994,7 @@ static void dwc2_hcd_free(struct dwc2_hsotg *hsotg)
>>
>> /* Free memory for QH/QTD lists */
>> dwc2_qh_list_free(hsotg, &hsotg->non_periodic_sched_inactive);
>> + dwc2_qh_list_free(hsotg, &hsotg->non_periodic_sched_waiting);
>> dwc2_qh_list_free(hsotg, &hsotg->non_periodic_sched_active);
>> dwc2_qh_list_free(hsotg, &hsotg->periodic_sched_inactive);
>> dwc2_qh_list_free(hsotg, &hsotg->periodic_sched_ready);
>> @@ -5151,6 +5157,7 @@ int dwc2_hcd_init(struct dwc2_hsotg *hsotg)
>>
>> /* Initialize the non-periodic schedule */
>> INIT_LIST_HEAD(&hsotg->non_periodic_sched_inactive);
>> + INIT_LIST_HEAD(&hsotg->non_periodic_sched_waiting);
>> INIT_LIST_HEAD(&hsotg->non_periodic_sched_active);
>>
>> /* Initialize the periodic schedule */
>> diff --git a/drivers/usb/dwc2/hcd.h b/drivers/usb/dwc2/hcd.h
>> index 11c3c145b793..af4f4360e8b7 100644
>> --- a/drivers/usb/dwc2/hcd.h
>> +++ b/drivers/usb/dwc2/hcd.h
>> @@ -313,12 +313,16 @@ struct dwc2_hs_transfer_time {
>> * descriptor and indicates original XferSize value for the
>> * descriptor
>> * @unreserve_timer: Timer for releasing periodic reservation.
>> + * @wait_timer: Timer used to wait before re-queuing.
>> * @dwc2_tt: Pointer to our tt info (or NULL if no tt).
>> * @ttport: Port number within our tt.
>> * @tt_buffer_dirty True if clear_tt_buffer_complete is pending
>> * @unreserve_pending: True if we planned to unreserve but haven't yet.
>> * @schedule_low_speed: True if we have a low/full speed component (either the
>> * host is in low/full speed mode or do_split).
>> + * @want_wait: We should wait before re-queuing; only matters for non-
>> + * periodic transfers and is ignored for periodic ones.
>> + * @wait_timer_cancel: Set to true to cancel the wait_timer.
>> *
>> * A Queue Head (QH) holds the static characteristics of an endpoint and
>> * maintains a list of transfers (QTDs) for that endpoint. A QH structure may
>> @@ -353,11 +357,14 @@ struct dwc2_qh {
>> u32 desc_list_sz;
>> u32 *n_bytes;
>> struct timer_list unreserve_timer;
>> + struct timer_list wait_timer;
>> struct dwc2_tt *dwc_tt;
>> int ttport;
>> unsigned tt_buffer_dirty:1;
>> unsigned unreserve_pending:1;
>> unsigned schedule_low_speed:1;
>> + unsigned want_wait:1;
>> + unsigned wait_timer_cancel:1;
>> };
>>
>> /**
>> @@ -388,6 +395,7 @@ struct dwc2_qh {
>> * @n_desc: Number of DMA descriptors for this QTD
>> * @isoc_frame_index_last: Last activated frame (packet) index, used in
>> * descriptor DMA mode only
>> + * @num_naks: Number of NAKs received on this QTD.
>> * @urb: URB for this transfer
>> * @qh: Queue head for this QTD
>> * @qtd_list_entry: For linking to the QH's list of QTDs
>> @@ -418,6 +426,7 @@ struct dwc2_qtd {
>> u8 error_count;
>> u8 n_desc;
>> u16 isoc_frame_index_last;
>> + u16 num_naks;
>> struct dwc2_hcd_urb *urb;
>> struct dwc2_qh *qh;
>> struct list_head qtd_list_entry;
>> diff --git a/drivers/usb/dwc2/hcd_intr.c b/drivers/usb/dwc2/hcd_intr.c
>> index 28a8210710b1..aad3abd2ddf2 100644
>> --- a/drivers/usb/dwc2/hcd_intr.c
>> +++ b/drivers/usb/dwc2/hcd_intr.c
>> @@ -52,6 +52,12 @@
>> #include "core.h"
>> #include "hcd.h"
>>
>> +/*
>> + * If we get this many NAKs on a split transaction we'll slow down
>> + * retransmission. A 1 here means delay after the first NAK.
>> + */
>> +#define DWC2_NAKS_BEFORE_DELAY 3
>> +
>> /* This function is for debug only */
>> static void dwc2_track_missed_sofs(struct dwc2_hsotg *hsotg)
>> {
>> @@ -1200,11 +1206,25 @@ static void dwc2_hc_nak_intr(struct dwc2_hsotg *hsotg,
>> /*
>> * Handle NAK for IN/OUT SSPLIT/CSPLIT transfers, bulk, control, and
>> * interrupt. Re-start the SSPLIT transfer.
>> + *
>> + * Normally for non-periodic transfers we'll retry right away, but to
>> + * avoid interrupt storms we'll wait before retrying if we've got
>> + * several NAKs. If we didn't do this we'd retry directly from the
>> + * interrupt handler and could end up quickly getting another
>> + * interrupt (another NAK), which we'd retry.
>> + *
>> + * Note that in DMA mode software only gets involved to re-send NAKed
>> + * transfers for split transactions, so we only need to apply this
>> + * delaying logic when handling splits. In non-DMA mode presumably we
>> + * might want a similar delay if someone can demonstrate this problem
>> + * affects that code path too.
>> */
>> if (chan->do_split) {
>> if (chan->complete_split)
>> qtd->error_count = 0;
>> qtd->complete_split = 0;
>> + qtd->num_naks++;
>> + qtd->qh->want_wait = qtd->num_naks >= DWC2_NAKS_BEFORE_DELAY;
>> dwc2_halt_channel(hsotg, chan, qtd, DWC2_HC_XFER_NAK);
>> goto handle_nak_done;
>> }
>> diff --git a/drivers/usb/dwc2/hcd_queue.c b/drivers/usb/dwc2/hcd_queue.c
>> index 3ae8b1bbaa55..bea0aadd756e 100644
>> --- a/drivers/usb/dwc2/hcd_queue.c
>> +++ b/drivers/usb/dwc2/hcd_queue.c
>> @@ -57,6 +57,9 @@
>> /* Wait this long before releasing periodic reservation */
>> #define DWC2_UNRESERVE_DELAY (msecs_to_jiffies(5))
>>
>> +/* If we get a NAK, wait this long before retrying */
>> +#define DWC2_RETRY_WAIT_DELAY (msecs_to_jiffies(1))
>> +
>> /**
>> * dwc2_periodic_channel_available() - Checks that a channel is available for a
>> * periodic transfer
>> @@ -1439,6 +1442,55 @@ static void dwc2_deschedule_periodic(struct dwc2_hsotg *hsotg,
>> list_del_init(&qh->qh_list_entry);
>> }
>>
>> +/**
>> + * dwc2_wait_timer_fn() - Timer function to re-queue after waiting
>> + *
>> + * As per the spec, a NAK indicates that "a function is temporarily unable to
>> + * transmit or receive data, but will eventually be able to do so without need
>> + * of host intervention".
>> + *
>> + * That means that when we encounter a NAK we're supposed to retry.
>> + *
>> + * ...but if we retry right away (from the interrupt handler that saw the NAK)
>> + * then we can end up with an interrupt storm (if the other side keeps NAKing
>> + * us) because on slow enough CPUs it could take us longer to get out of the
>> + * interrupt routine than it takes for the device to send another NAK. That
>> + * leads to a constant stream of NAK interrupts and the CPU locks.
>> + *
>> + * ...so instead of retrying right away in the case of a NAK we'll set a timer
>> + * to retry some time later. This function handles that timer and moves the
>> + * qh back to the "inactive" list, then queues transactions.
>> + *
>> + * @data: Pointer to a qh to re-schedule.
>> + */
>> +static void dwc2_wait_timer_fn(unsigned long data)
>> +{
>> + struct dwc2_qh *qh = (struct dwc2_qh *)data;
>> + struct dwc2_hsotg *hsotg = qh->hsotg;
>> + unsigned long flags;
>> +
>> + spin_lock_irqsave(&hsotg->lock, flags);
>> +
>> + /*
>> + * We'll set wait_timer_cancel to true if we want to cancel this
>> + * operation in dwc2_hcd_qh_unlink().
>> + */
>> + if (!qh->wait_timer_cancel) {
>> + enum dwc2_transaction_type tr_type;
>> +
>> + qh->want_wait = false;
>> +
>> + list_move(&qh->qh_list_entry,
>> + &hsotg->non_periodic_sched_inactive);
>> +
>> + tr_type = dwc2_hcd_select_transactions(hsotg);
>> + if (tr_type != DWC2_TRANSACTION_NONE)
>> + dwc2_hcd_queue_transactions(hsotg, tr_type);
>> + }
>> +
>> + spin_unlock_irqrestore(&hsotg->lock, flags);
>> +}
>> +
>> /**
>> * dwc2_qh_init() - Initializes a QH structure
>> *
>> @@ -1468,6 +1520,7 @@ static void dwc2_qh_init(struct dwc2_hsotg *hsotg, struct dwc2_qh *qh,
>> qh->hsotg = hsotg;
>> setup_timer(&qh->unreserve_timer, dwc2_unreserve_timer_fn,
>> (unsigned long)qh);
>> + setup_timer(&qh->wait_timer, dwc2_wait_timer_fn, (unsigned long)qh);
>
> Kees Cook started to replace setup_timer() with the new timer_setup(). I'm not sure if it's okay to use the deprecated function and replace all of them later.

I'm happy to do it either way. Personally I'd rather see my patch
land as-is and then have a followup patch that converts to
timer_setup(). That makes it easier for people like me who are always
backporting to older kernels. I'm also happy to either post that
patch myself or have someone else do it.


-Doug

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