All of lore.kernel.org
 help / color / mirror / Atom feed
From: Mathias Nyman <mathias.nyman@linux.intel.com>
To: Felipe Balbi <felipe.balbi@linux.intel.com>
Cc: Linux USB <linux-usb@vger.kernel.org>,
	Alan Stern <stern@rowland.harvard.edu>
Subject: [02/20] usb: host: xhci: check DYING state earlier
Date: Wed, 2 May 2018 14:38:22 +0300	[thread overview]
Message-ID: <0499213e-c195-bf4a-5175-5dedcdc8641a@linux.intel.com> (raw)

On 17.04.2018 10:07, Felipe Balbi wrote:
> 
> Hi,
> 
> Mathias Nyman <mathias.nyman@linux.intel.com> writes:
>> On 16.04.2018 15:29, Felipe Balbi wrote:
>>> Instead of allocating urb priv and, maybe, bail out due to xhci being
>>> in DYING state, we can move the check earlier and avoid the memory
>>> allocation altogether.
>>
>> This also moves checking for DYING outside the lock.
>>
>> Most cases set DYING with lock held, so if we first get the lock before
>> checking DYING we have a better chance of not being in the process of dying.
> 
> pretty sure that's atomic, though.

That's not what I'm after, your fix is cleaning up code in the case where DYING flag is
set before xhci_urb_enqueue() is called. I'm worried about the case when setting DYING flag races
with xhci_urb_enqueue(). i.e. xhci_urb_enqueue() is spinning on the lock, waiting, while
some other part of the driver is desperately trying to access hw with lock held, failing,
finally setting DYING flag, and then releasing lock.

If the check is done before taking the lock then the URB might be queued on dying device,
at a time when xhci_hc_died already started cancelling and giving back all queued URB

> 
>> Small thing, but so is this cleanup, so not sure its worth the change
> 
> Look at the result. With this change we don't need to take a lock,
> allocate memory, search for endpoint index, search for endpoint
> state. All of those are needed for proper operation of the function, but
> if the controller has already died, there's no point in going any
> further.

But we might miss the fact that host died, and go even further, adding URB to list,
writing TRBs to ringbuffers etc.

In code we save one line,
goto: free_priv

-Mathias
---
To unsubscribe from this list: send the line "unsubscribe linux-usb" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

             reply	other threads:[~2018-05-02 11:38 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-02 11:38 Mathias Nyman [this message]
  -- strict thread matches above, loose matches on Subject: below --
2018-05-02 14:11 [02/20] usb: host: xhci: check DYING state earlier Alan Stern
2018-05-02 13:02 Mathias Nyman
2018-05-02 11:46 Felipe Balbi
2018-04-17  7:07 Felipe Balbi
2018-04-16 13:31 Mathias Nyman
2018-04-16 12:29 Felipe Balbi

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=0499213e-c195-bf4a-5175-5dedcdc8641a@linux.intel.com \
    --to=mathias.nyman@linux.intel.com \
    --cc=felipe.balbi@linux.intel.com \
    --cc=linux-usb@vger.kernel.org \
    --cc=stern@rowland.harvard.edu \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.