Messages in this thread | | | Date | Mon, 26 Jan 2009 18:32:57 +0100 | From | Pavel Machek <> | Subject | Re: nbd: add locking to nbd_ioctl |
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> Pavel Machek wrote: > >>Pavel Machek wrote: > >>>>Pavel Machek wrote: > >>>>>On Fri 2009-01-16 10:24:06, Paul Clements wrote: > >>>>lo->sock is only modified under tx_lock (except for SET_SOCK, where the > >>>>device is being initialized, in which case it's impossible for any > >>>>other thread to be accessing the device) > >>>Well, unless the user is evil or confused? :-). > >>Even in that case, you're just going to get EBUSY. Nothing bad will > >>happen. SET_SOCK checks for lo->file, so it cannot be called on an > >>active nbd device. > >> > >> > >>>>As for other fields, I assume you're talking about blksize, et al. > >>>>Taking tx_lock doesn't prevent you from screwing yourself if you modify > >>>>those while the device is active. You'd need to disallow those ioctls > >>>>when the device is active (check lo->file). Again, this is only going > >>>>to happen if you really misuse the ioctls. > >>>Ok, I'll take a look at the missing checks. I'd really like to make > >>>this "stable" -- no amount of misuse should crash the kernel. > >>Just to summarize, I don't think we need to hold tx_lock around the > >>entirety of nbd_ioctl. We do need one extra tx_lock around xmit_timeout > >>and we do need to check for lo->file and return EBUSY in all of the > >>SET_*SIZE* ioctls. > > > >I could do that but it would be a bit too complex, and still rely on > >big kernel lock. Would you agree to patch that added tx_lock around > >all of it, and moved ioctl to unlocked ioctl? > > OK, I can buy the complexity argument. Your patch sounds fine to me.
Thanks for review! Pavel
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