linux-kernel - Re: [PATCH v2] mm: dmapool: use provided gfp flags for all dma_alloc

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Message-ID: <20130129110228.GA20242@lunn.ch>
Date:	Tue, 29 Jan 2013 12:02:28 +0100
From:	Andrew Lunn <andrew@...n.ch>
To:	Soeren Moch <smoch@....de>
Cc:	Andrew Lunn <andrew@...n.ch>, Arnd Bergmann <arnd@...db.de>,
	Jason Cooper <jason@...edaemon.net>,
	Greg KH <gregkh@...uxfoundation.org>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-kernel@...r.kernel.org, Michal Hocko <mhocko@...e.cz>,
	linux-mm@...ck.org, Kyungmin Park <kyungmin.park@...sung.com>,
	Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	linaro-mm-sig@...ts.linaro.org,
	linux-arm-kernel@...ts.infradead.org,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Subject: Re: [PATCH v2] mm: dmapool: use provided gfp flags for all
 dma_alloc_coherent() calls

> Now I activated the debug messages in em28xx. From the messages I
> see no correlation of the pool exhaustion and lost sync. Also I
> cannot see any error messages from the em28xx driver.
> I see a lot of init_isoc/stop_urbs (maybe EPG scan?) without
> draining the coherent pool (checked with 'cat
> /debug/dma-api/num_free_entries', which gave stable numbers), but
> after half an hour there are only init_isoc messages without
> corresponding stop_urbs messages and num_free_entries decreased
> until coherent pool exhaustion.

Hi Soeren

em28xx_stop_urbs() is only called by em28xx_stop_streaming().

em28xx_stop_streaming() is only called by em28xx_stop_feed()
when 0 == dvb->nfeeds.

em28xx_stop_feed()and em28xx_start_feed() look O.K, dvb->nfeeds is
protected by a mutex etc.

Now, em28xx_init_isoc() is also called by buffer_prepare(). This uses
em28xx_alloc_isoc() to do the actual allocation, and that function
sets up the urb such that on completion the function
em28xx_irq_callback() is called.

It looks like there might be issues here:

Once the data has been copied out, it resubmits the urb:

       urb->status = usb_submit_urb(urb, GFP_ATOMIC);
        if (urb->status) {
                em28xx_isocdbg("urb resubmit failed (error=%i)\n",
                               urb->status);
        }
  
However, if the ubs_submit_urb fails, it looks like the urb is lost.

If you look at other code submitting urbs you have this pattern:

               rc = usb_submit_urb(isoc_bufs->urb[i], GFP_ATOMIC);
                if (rc) {
                        em28xx_err("submit of urb %i failed (error=%i)\n", i,
                                   rc);
                        em28xx_uninit_isoc(dev, mode);
                        return rc;
                }
 
Do you have your build such that you would see "urb resubmit failed"
in your logs? Are there any?

     Andrew
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