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SubjectRe: [PATCH] bdev: fix NULL pointer dereference in sync()/close() race

On Sat, Aug 27, 2016 at 11:30:22AM +0200, Vegard Nossum wrote:
> > Don't know what's the right fix, but I posted a slightly different one
> > for the same crash some months ago:
> >
> >
> Ah, I'm sorry, I didn't see that.
> Your patch is 100% identical to my first attempt at a fix and I can
> confirm that it also fixes the problem for me.
> If people who are more savvy in block/fs code could ack the locking bits
> I think we should apply the patch ASAP because it's an easy local DOS if
> you have (open/read) access to any block device.

I think the right thing to do there is doing blkdev_get() /
blkdev_put() around func() invocation in iterate_bdevs() rather than
holding bd_mutex across the callback. Can you please verify whether
that works?



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