linux-kernel - Re: [PATCH 2/2] usb: host: xhci: Handle the right timeout command

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Date:   Thu, 22 Dec 2016 00:18:16 +0900
From:   OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:     Mathias Nyman <mathias.nyman@...ux.intel.com>
Cc:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Baolin Wang <baolin.wang@...aro.org>,
        Mathias Nyman <mathias.nyman@...el.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        USB <linux-usb@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>,
        "Lu\, Baolu" <baolu.lu@...el.com>,
        Alan Stern <stern@...land.harvard.edu>
Subject: Re: [PATCH 2/2] usb: host: xhci: Handle the right timeout command

Mathias Nyman <mathias.nyman@...ux.intel.com> writes:

>> We set CMD_RING_STATE_ABORTED state under locking. I'm not checking what
>> is for taking lock for register though, I guess it should be enough just
>> lock around of read=>write of ->cmd_ring if need lock.
>
> After your patch it should be enough to have the lock only while
> reading and writing the cmd_ring register.
>
> If we want a locking fix that applies more easily to older stable
> releases before your change then the lock needs to cover set
> CMD_RING_STATE_ABORT, read cmd_reg, write cmd_reg and busiloop
> checking CRR bit.  Otherwise the stop cmd ring interrupt handler may
> restart the ring just before we start checing CRR. The stop cmd ring
> interrupt will set the CMD_RING_STATE_ABORTED to
> CMD_RING_STATE_RUNNING so ring will really restart in the interrupt
> handler.

Just for record (no chance to make patch I myself for now, sorry), while
checking locking slightly, I noticed unrelated missing locking.

	xhci_cleanup_command_queue()

We are calling it without locking, but we need to lock for accessing list.

Thanks.
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>