Re: [Bug #14016] mm/ipw2200 regression

Mel Gorman
2009-08-26T09:37:49Z

On Wed, Aug 26, 2009 at 10:27:41AM +0200, Johannes Weiner wrote:
> [Cc netdev]
>
> On Wed, Aug 26, 2009 at 09:09:44AM +0300, Pekka Enberg wrote:
> > On Tue, Aug 25, 2009 at 11:34 PM, Rafael J. Wysocki<rjw-KKrjLPT3xs0@public.gmane.org> wrote:
> > > This message has been generated automatically as a part of a report
> > > of recent regressions.
> > >
> > > The following bug entry is on the current list of known regressions
> > > from 2.6.30.  Please verify if it still should be listed and let me know
> > > (either way).
> > >
> > > Bug-Entry       : http://bugzilla.kernel.org/show_bug.cgi?id=14016
> > > Subject         : mm/ipw2200 regression
> > > Submitter       : Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
> > > Date            : 2009-08-15 16:56 (11 days old)
> > > References      : http://marc.info/?l=linux-kernel&m=125036437221408&w=4
> >
> > If am reading the page allocator dump correctly, there's plenty of
> > pages left but we're unable to satisfy an order 6 allocation. There's
> > no slab allocator involved so the page allocator changes that went
> > into 2.6.31 seem likely. Mel, ideas?
>
> It's an atomic order-6 allocation, the chances for this to succeed
> after some uptime become infinitesimal. The chunks > order-2 are
> pretty much exhausted on this dump.
>
> 64 pages, presumably 256k, for fw->boot_size while current ipw
> firmware images have ~188k. I don't know jack squat about this
> driver, but given the field name and the struct:
>
> struct ipw_fw {
> __le32 ver;
> __le32 boot_size;
> __le32 ucode_size;
> __le32 fw_size;
> u8 data[0];
> };
>
> fw->boot_size alone being that big sounds a bit fishy to me.
>

Agreed. While there are a low number of order-6 pages free in the page
allocation failure dump, there are not enough for watermarks to be
satisified. As it's atomic, there is little that can be done from a VM
perspective and it's the responsibility of the driver. I'm no driver expert
but I'll have a go at fixing it anyway.

My reading of this is that the firmware is being loaded from a workqueue and
I am failing to see any restriction on sleeping in the path. It would appear
that the driver just used the most convenient *_alloc_coherent function
available forgetting that it assumes GFP_ATOMIC. Can someone who does know
which way is up with a driver tell me why the patch below might not
work?

Bartlomiej, any chance you could give this a spin? Preferably, you'd
have preempt enabled and CONFIG_DEBUG_SPINLOCK_SLEEP on as well because
that combination will complain loudly if we really can't sleep in this
path.

=====
ipw2200: Avoid large GFP_ATOMIC allocation during firmware loading

ipw2200 uses pci_alloc_consistent() to allocate a large coherent buffer for
the loading of firmware which is an order-6 allocation of GFP_ATOMIC. At
system start-up time, this is not a problem. However, the firmware on the
card can get confused and the corrective action taken is to reload the
firmware and reinit the card. High-order GFP_ATOMIC allocations of this
type can and will fail when the system is already up and running.

As the firmware is loaded from a workqueue, it should be possible for
the driver to go to sleep. This patch converts the call of
pci_alloc_consistent() which assumes GFP_ATOMIC to dma_alloc_coherent()
which can specify its own flags.

The big downside with this patch is that it uses GFP_REPEAT to avoid the
driver unloading. There is potential that this will cause a reclaim
storm as the machine tries to find a free order-6 buffer. A suggested
alternative for the driver owner is in the comments.

Signed-off-by: Mel Gorman <mel-wPRd99KPJ+uzQB+pC5nmwQ@public.gmane.org>
---
drivers/net/wireless/ipw2x00/ipw2200.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/ipw2x00/ipw2200.c b/drivers/net/wireless/ipw2x00/ipw2200.c
index 44c29b3..f2e251e 100644
--- a/drivers/net/wireless/ipw2x00/ipw2200.c
+++ b/drivers/net/wireless/ipw2x00/ipw2200.c
@@ -3167,7 +3167,19 @@ static int ipw_load_firmware(struct ipw_priv *priv, u8 * data, size_t len)
u8 *shared_virt;

IPW_DEBUG_TRACE("<< : \n");
- shared_virt = pci_alloc_consistent(priv->pci_dev, len, &shared_phys);
+
+ /*
+ * This is a whopping large allocation, in or around order-6 so
+ * dma_alloc_coherent is used to specify the GFP_KERNEL|__GFP_REPEAT
+ * flags. Note that this action means the system could go into a
+ * reclaim loop until it cannot reclaim any more trying to satisfy
+ * the allocation. It would be preferable if one buffer is allocated
+ * at driver initialisation and reused when the firmware needs to
+ * be reloaded, overwriting the existing firmware each time
+ */
+ shared_virt = dma_alloc_coherent(
+ priv->pci_dev == NULL ? NULL : &priv->pci_dev->dev,
+ len, &shared_phys, GFP_KERNEL|__GFP_REPEAT);

if (!shared_virt)
return -ENOMEM;