Re: bdi: register sysfs bdi device only once per queue

Andrew Morton
2008-11-05T20:11:20Z

On Mon, 03 Nov 2008 17:08:50 +0100
Peter Zijlstra <peterz@infradead.org> wrote:

> On Mon, 2008-11-03 at 16:53 +0100, Kay Sievers wrote:
> > Andrew, can you pick this up this please?
> >
> > Thanks,
> > Kay
> >
> >
> > From: Kay Sievers <kay.sievers@vrfy.org>
> > Subject: bdi: register sysfs bdi device only once per queue
> >
> > Devices which share the same queue, like floppies and mtd devices,
> > get registered multiple times in the bdi interface, but bdi accounts
> > only the last registered device of the devices sharing one queue.
>
> David, is there any reason the mtd devices do this?

[tap tap - is this thing turned on?]

> > On remove, all earlier registered devices leak, stay around in
> > sysfs, and cause "duplicate filename" errors if the devices are
> > re-created.
> >
> > This prevents the creation of multiple bdi interfaces per queue,
> > and the bdi device will carry the dev_t name of the block device
> > which is the first one registered, of the pool of devices using
> > the same queue.
> >
> > Tested-By: Peter Korsgaard <jacmet@sunsite.dk>
> > Acked-By: Peter Zijlstra <a.p.zijlstra@chello.nl>
> > Signed-Off-By: Kay Sievers <kay.sievers@vrfy.org>
> > ---
> >
> > diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> > index f2e574d..e6676e5 100644
> > --- a/mm/backing-dev.c
> > +++ b/mm/backing-dev.c
> > @@ -176,6 +176,9 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
> > int ret = 0;
> > struct device *dev;
> >
> > + if (bdi->dev)
> > + goto exit;
> > +
> > va_start(args, fmt);
> > dev = device_create_vargs(bdi_class, parent, MKDEV(0, 0), bdi, fmt, args);
> > va_end(args);
>
> Would it make sense to make it print something like, please fix me?

Yes, I think it would.

--- a/mm/backing-dev.c~bdi-register-sysfs-bdi-device-only-once-per-queue-fix
+++ a/mm/backing-dev.c
@@ -176,7 +176,7 @@ int bdi_register(struct backing_dev_info
int ret = 0;
struct device *dev;

- if (bdi->dev)
+ if (WARN_ON(bdi->dev))
goto exit;

va_start(args, fmt);
_

It's a bit cheeky to add a known-to-trigger WARN_ON into -rc4 but if we
don't do this then the issue will just get swept under the carpet.