On Wed, 27 Oct 2010, John Baldwin wrote:
On Wednesday, October 27, 2010 7:33:13 am Sergey Kandaurov wrote:
On 27 October 2010 10:23, Lars Hartmann <[email protected]> wrote:
The vgonel function isnt declarated in any header, the vgonel prototype
in vgone(9) isnt correct - found by Ben Kaduk <[email protected]>
Hi.
I'm afraid it's just an overlooked man page after many VFS changes in 5.x.
As vgonel() is a static (i.e. private and not visible from outside) function
IMO it should be removed from vgone(9) man page.
Agreed. It certainly should not be added to vnode.h. I'm curious how the
reporter is getting a warning since there is a static prototype for vgonel()
in vfs_subr.c.
It's for a third-party kernel module, for the OpenAFS filesystem (which
has been unloved for FreeBSD since the 4.X days). The AFS code is
currently using unlocked accesses to v_usecount (which, unsurprisingly,
led to a race condition that caused an invariant check to fail), and I was
going through and adding the interlock around them. At the place that I
suspect to be the main cause of this race [1], the usecount was checked to
be nonpositive along with a couple other conditions, and a little later
vgone() was called. Holding the interlock across both of these calls (and
therefore using vgonel()) seems to have closed the race condition I was
seeing. (Other checks of v_usecount were changed to grab the interlock,
but drop it before doing anything else.)
However, looking at the commit message for vfs_subr.c:1.631, I guess this
is not the locking strategy I'm supposed to be using?
I saw a warning of implicit declaration when compiling the kernel module,
but the kernel linker was happy to load it. I forget whether it matters
that vgonel is only declared static at its declaration but not its
definition.
-Ben Kaduk
[1] The old (racy) function is osi_TryEvictVCache, here:
http://git.openafs.org/?p=openafs.git;a=blob;f=src/afs/FBSD/osi_vcache.c;h=c2060c74f0155a610d2ea94f3c7f508e8ca4373a;hb=HEAD
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