Re: [PATCH -tip] remove the BKL: Replace BKL in mount/umount syscalls with a mutex

[Al Viro <viro@ZenIV.linux.org.uk>]

On Fri, Apr 17, 2009 at 02:01:42AM +0200, Ingo Molnar wrote:
> 
> * Al Viro <viro@ZenIV.linux.org.uk> wrote:
> 
> > remount is potentially nastier, but then it *is* nasty.  Again, 
> > it's only per-fs stuff, so the obvious first step is taking BKL 
> > down into the instances. It doesn't protect anything in VFS; all 
> > uses are fs internal, so that'll take review of individual 
> > filesystems.
> > 
> > NOTE: do not assume that code in fs/foo/* is correct; "it doesn't 
> > take BKL elsewhere" does _not_ mean that we don't have races.  
> > IOW, the same review ought to look for such beasts and deal with 
> > them.  Mere "oh, no BKL anywhere in that fs" is not enough to 
> > discard the ->remount_fs() instance.
> 
> what kind of races do you mean? Timing sensitive ones that are there 
> just are not easy to trigger with the BKL held?
> 
> Or actual locking interaction between that body of BKL code and all 
> other BKL using code?

Old foo_read_super/foo_write_super/foo_put_super/foo_remount_fs for the
same foo.  IOW, per-driver (and not per-fs - that's taken care of) data
structures.  Arbitrary weird ones.