Messages in this thread | | | Date | Wed, 26 Feb 2003 13:32:46 +0000 (GMT) | From | Hugh Dickins <> | Subject | Re: [OOPS] 2.5.63 - NULL pointer dereference in loop device |
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On Tue, 25 Feb 2003, Jonah Sherman wrote: > On Tue, Feb 25, 2003 at 09:15:56PM +0000, Hugh Dickins wrote: > > If you "losetup /dev/loop0 /dev/hdN", then it's LO_FLAGS_BH_REMAP > > and doesn't even call bio_copy: it doesn't copy bio or buffers or > > It appears this way if you just look at none_status, but you didn't look > at loop_init_xfer(). Notice that it doesn't call xfer->init unless > type != 0, so that flag is infact never set.
Hah! Indeed, thank you for setting me straight.
> > Can you shed more light on how to reproduce this? > > The block dev it is being used on must be larger than your RAM. I don't > have any swap on this machine, so I don't know if it must be bigger than > that too. Maybe disabling swap before testing this oops will make it > work?
Yes, I'd tried block dev larger than RAM, with and without swap: no luck. Perhaps my disks somehow keep up with the stuff coming down from /dev/zero but yours don't? (No disgrace!) But never mind, Andrew has a surer way to hit it.
> In any case, the patch sent by Andrew Morton fixed this bug.
Andrew's patch for this is a thing of great beauty, a shining beacon to inspire all whose eyes are graced by it. But I'd still have liked to understand why it's needed in your case not mine: it's a bit embarrassing for me to claim I have patches for various loopmem hangs, yet be unable to reproduce this.
Hugh
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