The state of Giant lock in the file systems?

John Baldwin jhb at
Mon Nov 8 15:05:10 UTC 2010

On Monday, November 08, 2010 7:28:26 am Ivan Voras wrote:
> I was looking at fusefs sources and there is a dance it does with the
> Giant lock which looks fishy.
> 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() (???)
> 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?
> Would it be correct to think that coda is the single biggest obstacle?

Err, all the VFS_LOCK_GIANT() stuff for filesystems that do not have 
MNTK_MPSAFE set.  I believe the currently MPSAFE fs's are UFS, ZFS, MSDOSFS,
CD9660, UDF, NFS client, and devfs.  I think all others are !MPSAFE still.

John Baldwin

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