linux-kernel - Re: [PATCH 1/2] block: don't propagate unlisted DISK

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Message-ID: <BANLkTinwPt=aRSsh_Ppb8hLOaURh6mL2GQ@mail.gmail.com>
Date:	Thu, 21 Apr 2011 10:25:35 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Jens Axboe <jaxboe@...ionio.com>, Christoph Hellwig <hch@....de>,
	Neil Brown <neilb@...e.de>,
	"David S. Miller" <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org,
	kay.sievers@...y.org
Subject: Re: [PATCH 1/2] block: don't propagate unlisted DISK_EVENTs to userland

Should I take these as patches, or through Jens/David/Who?

I'll happily take them as patches, but I'd also like to hear
confirmation from the people who saw the lock-up that it's gone now..

                        Linus

On Thu, Apr 21, 2011 at 10:08 AM, Tejun Heo <tj@...nel.org> wrote:
> DISK_EVENT_MEDIA_CHANGE is used for both userland visible event and
> internal event for revalidation of removeable devices.  Some legacy
> drivers don't implement proper event detection and continuously
> generate events under certain circumstances.  For example, ide-cd
> generates media changed continuously if there's no media in the drive,
> which can lead to infinite loop of events jumping back and forth
> between the driver and userland event handler.
>
> This patch updates disk event infrastructure such that it never
> propagates events not listed in disk->events to userland.  Those
> events are processed the same for internal purposes but uevent
> generation is suppressed.
>
> This also ensures that userland only gets events which are advertised
> in the @events sysfs node lowering risk of confusion.
>
> Signed-off-by: Tejun Heo <tj@...nel.org>
> ---
> These two patches fix infinite MEDIA_CHANGE events problem reported w/
> ide-cd.  I tried an alternate patch to implement proper check_events()
> for ide-cd but given the deprecated status of ide and the existence of
> fallback userland event polling, this minimal approach seems better.
>
> Thank you.
>
>  block/genhd.c |    8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> Index: work/block/genhd.c
> ===================================================================
> --- work.orig/block/genhd.c
> +++ work/block/genhd.c
> @@ -1588,9 +1588,13 @@ static void disk_events_workfn(struct wo
>
>        spin_unlock_irq(&ev->lock);
>
> -       /* tell userland about new events */
> +       /*
> +        * Tell userland about new events.  Only the events listed in
> +        * @disk->events are reported.  Unlisted events are processed the
> +        * same internally but never get reported to userland.
> +        */
>        for (i = 0; i < ARRAY_SIZE(disk_uevents); i++)
> -               if (events & (1 << i))
> +               if (events & disk->events & (1 << i))
>                        envp[nr_events++] = disk_uevents[i];
>
>        if (nr_events)
>
--
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