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Re: Re2: NFS Stability


To: Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx>
From: Raphael Marmier <raphael@xxxxxxxxxxx>
Date: Wed, 06 Apr 2005 13:51:06 +0200

Just tried it. Bad news:

dragonfly# /usr/src/test/stress/fsx/dotest
Chance of close/open is 1 in 100000
truncating to largest ever: 0x2abbd1
truncating to largest ever: 0x3abe49
truncating to largest ever: 0x3b1956

Raphael

Matthew Dillon wrote:
Scratch that last patch. Try this one instead. I blew a check.

    If other people would like to help, what we are trying to do here
    is test an NFS client with the 'fsx' program and 'dotest' script found in
    /usr/src/test/stress/fsx.  To run the test you must have two machines
    and run it in a directory on the client that is mounted from the server
    r/w.

-Matt


Index: nfs_vnops.c
===================================================================
RCS file: /cvs/src/sys/vfs/nfs/nfs_vnops.c,v
retrieving revision 1.38
diff -u -r1.38 nfs_vnops.c
--- nfs_vnops.c 17 Mar 2005 17:28:46 -0000 1.38
+++ nfs_vnops.c 6 Apr 2005 05:42:57 -0000
@@ -736,13 +736,23 @@
return (EROFS);
/*
- * We run vnode_pager_setsize() early (why?),
- * we must set np->n_size now to avoid vinvalbuf
- * V_SAVE races that might setsize a lower
- * value.
+ * This is nasty. The RPCs we send to flush pending
+ * data often return attribute information which is
+ * cached via a callback to nfs_loadattrcache(), which
+ * has the effect of changing our notion of the file
+ * size. Due to flushed appends and other operations
+ * the file size can be set to virtually anything, + * including values that do not match either the old
+ * or intended file size.
+ *
+ * When this condition is detected we must loop to
+ * try the operation again. Hopefully no more
+ * flushing is required on the loop so it works the
+ * second time around. THIS CASE ALMOST ALWAYS
+ * HAPPENS!
*/
-
tsize = np->n_size;
+again:
error = nfs_meta_setsize(vp, ap->a_td, vap->va_size);
if (np->n_flag & NLMODIFIED) {
@@ -750,30 +760,34 @@
error = nfs_vinvalbuf(vp, 0, ap->a_td, 1);
else
error = nfs_vinvalbuf(vp, V_SAVE, ap->a_td, 1);
- if (error) {
- np->n_size = tsize;
- vnode_pager_setsize(vp, np->n_size);
- return (error);
- }
}
- /* - * np->n_size has already been set to vap->va_size
- * in nfs_meta_setsize(). We must set it again since
- * nfs_loadattrcache() could be called through
- * nfs_meta_setsize() and could modify np->n_size.
- *
- * (note that nfs_loadattrcache() will have called
- * vnode_pager_setsize() for us in that case).
+ /*
+ * note: this loop case almost always happens at + * least once per truncation.
*/
- np->n_vattr.va_size = np->n_size = vap->va_size;
+ if (error == 0 && np->n_size != vap->va_size)
+ goto again;
+ np->n_vattr.va_size = vap->va_size;
break;
}
} else if ((vap->va_mtime.tv_sec != VNOVAL ||
vap->va_atime.tv_sec != VNOVAL) && (np->n_flag & NLMODIFIED) &&
vp->v_type == VREG &&
- (error = nfs_vinvalbuf(vp, V_SAVE, ap->a_td, 1)) == EINTR)
+ (error = nfs_vinvalbuf(vp, V_SAVE, ap->a_td, 1)) == EINTR
+ ) {
return (error);
+ }
error = nfs_setattrrpc(vp, vap, ap->a_cred, ap->a_td);
+
+ /*
+ * Sanity check if a truncation was issued. This should only occur
+ * if multiple processes are racing on the same file.
+ */
+ if (error == 0 && vap->va_size != VNOVAL && + np->n_size != vap->va_size) {
+ printf("NFS ftruncate: server disagrees on the file size: %lld/%lld/%lld\n", tsize, vap->va_size, np->n_size);
+ goto again;
+ }
if (error && vap->va_size != VNOVAL) {
np->n_size = np->n_vattr.va_size = tsize;
vnode_pager_setsize(vp, np->n_size);



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