Messages in this thread | | | Date | Thu, 16 Apr 2009 13:01:50 -0400 | From | Christoph Hellwig <> | Subject | Re: [PATCH -tip] remove the BKL: Replace BKL in mount/umount syscalls with a mutex |
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On Thu, Apr 16, 2009 at 06:49:27PM +0200, Ingo Molnar wrote: > They dont really protect anything - the patch is wrong and > equivalent to a plain removal of the BKL. > > The only case we found to ever matter in practice is NFS: it really > wants to get rid of the BKL in nfsd_get_sb(). So pushing down the > BKL lock into per filesystems and then removing it from NFS should > do the trick. > > Would be nice to have some tentative Ack (or, a tentative > non-immediate-NAK) from Al before we go touch a lot of filesystems > though. Stupid dont-waste-human-effort considerations and stuff. > > For us, the much simpler solution would be to drop the BKL in > nfsd_get_sb() and go on with life without to touch a dozen or so > filesystems. Alessio, mind trying that too, is it a solution for > your testcase?
What about trying to attack it piece-mail? ->unmount_begin is really easy. The only one that doesn't protect everything properly is 9p, but it doesn't protect the state variable deep down a few levels of function calls at all.
->remount_fs should be easy enough to, we do have proper per-sb protection here, but do_remount_sb will need a bit of an audit. (and of course pushing lock_kernel down into the many instances and leave the cleanup-work to the fs maintainers).
The actual mount path is more interesting as there are quite a few cases there. As a first step you can take lock_kernel from outside do_mount into the various do_foo calls inside it, and then work on those piece by piece.
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