Date: Mon, 8 Nov 2010 16:31:30 +0200 From: Gleb Kurtsou <gleb.kurtsou@gmail.com> To: Ivan Voras <ivoras@freebsd.org> Cc: freebsd-fs@freebsd.org Subject: Re: The state of Giant lock in the file systems? Message-ID: <20101108143130.GA2799@tops> In-Reply-To: <ib8qda$nat$1@dough.gmane.org> References: <ib8qda$nat$1@dough.gmane.org>
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On (08/11/2010 13:28), Ivan Voras wrote: > I was looking at fusefs sources and there is a dance it does with the > Giant lock which looks fishy. It's intended to be fishy. No kernel level locks should be held before returning to userland, in other words on each syscall vnode is locked (+ Gaint lock for fs if needed), than it's unlocked by filesystem and relocked upon callback from userspace. puffs is MPSAFE if that could be of any help for you. > Grepping for "-ir giant" in /sys/fs on 8-stable shows only a handful of > mentionings, but if I understand it correctly only these "active" instances: > > 1) one set of mtx_assert() calls on it in pseudofs, which I can't figure > out what they're guarding > 2) some manual locking and unlocking in nfsclient which appears to only > guard printf() (???) Somewhat unrelated, but. Does NFS client unlock vnodes while sending/waiting for RCP reply? I thought it does, but I'm not sure. > 3) some more locking in nfsserver which apparently is only there to > guard the underlying local file system > 4) coda, which appears to be the only one marked with D_NEEDGIANT, but > doesn't do much of its own interfacing with it > > Except for these, is there any more magic that would need to be resolved > to excise Giant from VFS? Kostik was working on it. > Would it be correct to think that coda is the single biggest obstacle? Filesystem should be marked as MPSAFE, it's not D_NEEDGIANT flag but MNTK_MPSAFE. A lot of filesystems are still locked by Gaint, i.e ext2fs, smbfs, nwfs, ntfs, etc. > > _______________________________________________ > freebsd-fs@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-fs > To unsubscribe, send any mail to "freebsd-fs-unsubscribe@freebsd.org"
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