Core Dump / panic sleeping thread

[Konstantin Belousov]

On Wed, Mar 20, 2013 at 11:37:56AM -0400, Rick Macklem wrote:
> Konstantin Belousov wrote:
> > On Wed, Mar 20, 2013 at 12:13:05PM +0100, Michael Landin Hostbaek
> > wrote:
> > >
> > > On Mar 20, 2013, at 10:49 AM, Konstantin Belousov
> > > <kostikbel at gmail.com> wrote:
> > > >
> > > > I do not like it. As I said in the previous response to Andrey,
> > > > I think that moving the vnode_pager_setsize() after the unlock is
> > > > better, since it reduces races with other thread seeing half-done
> > > > attribute update or making attribute change simultaneously.
> > >
> > > OK - so should I wait for another patch - or?
> > 
> > I think the following is what I mean. As an additional note, why nfs
> > client does not trim the buffers when server reported node size change
> > ?
> > 
> > diff --git a/sys/fs/nfsclient/nfs_clport.c
> > b/sys/fs/nfsclient/nfs_clport.c
> > index a07a67f..4fe2e35 100644
> > --- a/sys/fs/nfsclient/nfs_clport.c
> > +++ b/sys/fs/nfsclient/nfs_clport.c
> > @@ -361,6 +361,8 @@ nfscl_loadattrcache(struct vnode **vpp, struct
> > nfsvattr *nap, void *nvaper,
> > struct nfsnode *np;
> > struct nfsmount *nmp;
> > struct timespec mtime_save;
> > + u_quad_t nsize;
> > + int setnsize;
> > 
> > /*
> > * If v_type == VNON it is a new node, so fill in the v_type,
> > @@ -418,6 +420,7 @@ nfscl_loadattrcache(struct vnode **vpp, struct
> > nfsvattr *nap, void *nvaper,
> > } else
> > vap->va_fsid = vp->v_mount->mnt_stat.f_fsid.val[0];
> > np->n_attrstamp = time_second;
> > + setnsize = 0;
> > if (vap->va_size != np->n_size) {
> > if (vap->va_type == VREG) {
> > if (dontshrink && vap->va_size < np->n_size) {
> > @@ -444,10 +447,13 @@ nfscl_loadattrcache(struct vnode **vpp, struct
> > nfsvattr *nap, void *nvaper,
> > np->n_size = vap->va_size;
> > np->n_flag |= NSIZECHANGED;
> > }
> > - vnode_pager_setsize(vp, np->n_size);
> > } else {
> > np->n_size = vap->va_size;
> > }
> > + if (vap->va_type == VREG || vap->va_type == VDIR) {
> > + setnsize = 1;
> > + nsize = vap->va_size;
> I might have used np->n_size here, since that is what is given
> as the argument for the pre-patched version, but since
> np->n_size should equal vap->va_size (it is set the same for
> all cases in the code at this point), it doesn't really matter.
> 
> I have no idea what the implications of doing vnode_pager_setsize()
> for VDIR is, but Kostik would be much more conversant that I on this,
> so if he thinks it's ok, that's fine with me.
> 
> > + }
> > }
> > /*
> > * The following checks are added to prevent a race between (say)
> > @@ -480,6 +486,8 @@ nfscl_loadattrcache(struct vnode **vpp, struct
> > nfsvattr *nap, void *nvaper,
> > KDTRACE_NFS_ATTRCACHE_LOAD_DONE(vp, vap, 0);
> > #endif
> > NFSUNLOCKNODE(np);
> > + if (setnsize)
> > + vnode_pager_setsize(vp, nsize);
> > return (0);
> > }
> Yes, I think Kostik's version of the patch is good. I had thought
> of doing it that way, but want for the "minimal change" version.
> I agree that avoiding unlocking/relocking the mutex is a good idea,
> although I didn't see anything after the relock that I thought
> might be an issue if something changed while unlocked.
If the parallel calls to nfscl_loadattrcache() are possible, then
IMHO at least the n_attrstamp could be cleared needlessly.

> 
> Kostik, thanks for posting this version, rick
> ps: Michael, I'd suggest you try this patch instead of mine.
Still, my patch has the issue I noted for the head as well: the buffers
are not destroyed if the size of the vnode is decreased. I would be
inclined to suggest the following change on top of my patch, but I am
sure that it does not work, since vnode is generally not locked in
the nfs_loadattrcache(), I think:

diff --git a/sys/fs/nfsclient/nfs_clport.c b/sys/fs/nfsclient/nfs_clport.c
index 4fe2e35..3a08424 100644
--- a/sys/fs/nfsclient/nfs_clport.c
+++ b/sys/fs/nfsclient/nfs_clport.c
@@ -487,7 +487,7 @@ nfscl_loadattrcache(struct vnode **vpp, struct nfsvattr *nap, void *nvaper,
 #endif
 	NFSUNLOCKNODE(np);
 	if (setnsize)
-		vnode_pager_setsize(vp, nsize);
+		vtruncbuf(vp, NOCRED, nsize, vp->v_bufobj.bo_bsize);
 	return (0);
 }
 
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