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PR# 165923 reported intermittent write failures for dirty

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memory mapped pages being written back on an NFS mount.
Since any thread can call VOP_PUTPAGES() to write back a
dirty page, the credentials of that thread may not have
write access to the file on an NFS server. (Often the uid
is 0, which may be mapped to "nobody" in the NFS server.)
Although there is no completely correct fix for this
(NFS servers check access on every write RPC instead of at
open/mmap time), this patch avoids the common cases by
holding onto a credential that recently opened the file
for writing and uses that credential for the write RPCs
being done by VOP_PUTPAGES() for both NFS clients.

Tested by:	Joel Ray Holveck (joelh at juniper.net)
PR:		kern/165923
Reviewed by:	kib
MFC after:	2 weeks
This commit is contained in:
Rick Macklem 2012-05-12 12:02:51 +00:00
parent 2963a15591
commit 7af1242a34
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=235332
8 changed files with 50 additions and 2 deletions
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7
sys/fs/nfsclient/nfs_clbio.c
View file

@ -281,7 +281,11 @@ ncl_putpages(struct vop_putpages_args *ap)
vp = ap->a_vp;
np = VTONFS(vp);
td = curthread; /* XXX */
cred = curthread->td_ucred; /* XXX */
/* Set the cred to n_writecred for the write rpcs. */
if (np->n_writecred != NULL)
cred = crhold(np->n_writecred);
else
cred = crhold(curthread->td_ucred); /* XXX */
nmp = VFSTONFS(vp->v_mount);
pages = ap->a_m;
count = ap->a_count;
@ -345,6 +349,7 @@ ncl_putpages(struct vop_putpages_args *ap)
iomode = NFSWRITE_FILESYNC;
error = ncl_writerpc(vp, &uio, cred, &iomode, &must_commit, 0);
crfree(cred);
pmap_qremove(kva, npages);
relpbuf(bp, &ncl_pbuf_freecnt);

2
sys/fs/nfsclient/nfs_clnode.c
View file

@ -300,6 +300,8 @@ ncl_reclaim(struct vop_reclaim_args *ap)
FREE((caddr_t)dp2, M_NFSDIROFF);
}
}
if (np->n_writecred != NULL)
crfree(np->n_writecred);
FREE((caddr_t)np->n_fhp, M_NFSFH);
if (np->n_v4 != NULL)
FREE((caddr_t)np->n_v4, M_NFSV4NODE);

16
sys/fs/nfsclient/nfs_clvnops.c
View file

@ -513,6 +513,7 @@ nfs_open(struct vop_open_args *ap)
struct vattr vattr;
int error;
int fmode = ap->a_mode;
struct ucred *cred;
if (vp->v_type != VREG && vp->v_type != VDIR && vp->v_type != VLNK)
return (EOPNOTSUPP);
@ -604,7 +605,22 @@ nfs_open(struct vop_open_args *ap)
}
np->n_directio_opens++;
}
/*
* If this is an open for writing, capture a reference to the
* credentials, so they can be used by ncl_putpages(). Using
* these write credentials is preferable to the credentials of
* whatever thread happens to be doing the VOP_PUTPAGES() since
* the write RPCs are less likely to fail with EACCES.
*/
if ((fmode & FWRITE) != 0) {
cred = np->n_writecred;
np->n_writecred = crhold(ap->a_cred);
} else
cred = NULL;
mtx_unlock(&np->n_mtx);
if (cred != NULL)
crfree(cred);
vnode_create_vobject(vp, vattr.va_size, ap->a_td);
return (0);
}

1
sys/fs/nfsclient/nfsnode.h
View file

@ -123,6 +123,7 @@ struct nfsnode {
int n_directio_asyncwr;
u_int64_t n_change; /* old Change attribute */
struct nfsv4node *n_v4; /* extra V4 stuff */
struct ucred *n_writecred; /* Cred. for putpages */
};
#define n_atim n_un1.nf_atim

7
sys/nfsclient/nfs_bio.c
View file

@ -275,7 +275,11 @@ nfs_putpages(struct vop_putpages_args *ap)
vp = ap->a_vp;
np = VTONFS(vp);
td = curthread; /* XXX */
cred = curthread->td_ucred; /* XXX */
/* Set the cred to n_writecred for the write rpcs. */
if (np->n_writecred != NULL)
cred = crhold(np->n_writecred);
else
cred = crhold(curthread->td_ucred); /* XXX */
nmp = VFSTONFS(vp->v_mount);
pages = ap->a_m;
count = ap->a_count;
@ -339,6 +343,7 @@ nfs_putpages(struct vop_putpages_args *ap)
iomode = NFSV3WRITE_FILESYNC;
error = (nmp->nm_rpcops->nr_writerpc)(vp, &uio, cred, &iomode, &must_commit);
crfree(cred);
pmap_qremove(kva, npages);
relpbuf(bp, &nfs_pbuf_freecnt);

2
sys/nfsclient/nfs_node.c
View file

@ -270,6 +270,8 @@ nfs_reclaim(struct vop_reclaim_args *ap)
free((caddr_t)dp2, M_NFSDIROFF);
}
}
if (np->n_writecred != NULL)
crfree(np->n_writecred);
if (np->n_fhsize > NFS_SMALLFH) {
free((caddr_t)np->n_fhp, M_NFSBIGFH);
}

16
sys/nfsclient/nfs_vnops.c
View file

@ -507,6 +507,7 @@ nfs_open(struct vop_open_args *ap)
struct vattr vattr;
int error;
int fmode = ap->a_mode;
struct ucred *cred;
if (vp->v_type != VREG && vp->v_type != VDIR && vp->v_type != VLNK)
return (EOPNOTSUPP);
@ -563,7 +564,22 @@ nfs_open(struct vop_open_args *ap)
}
np->n_directio_opens++;
}
/*
* If this is an open for writing, capture a reference to the
* credentials, so they can be used by nfs_putpages(). Using
* these write credentials is preferable to the credentials of
* whatever thread happens to be doing the VOP_PUTPAGES() since
* the write RPCs are less likely to fail with EACCES.
*/
if ((fmode & FWRITE) != 0) {
cred = np->n_writecred;
np->n_writecred = crhold(ap->a_cred);
} else
cred = NULL;
mtx_unlock(&np->n_mtx);
if (cred != NULL)
crfree(cred);
vnode_create_vobject(vp, vattr.va_size, ap->a_td);
return (0);
}

1
sys/nfsclient/nfsnode.h
View file

@ -128,6 +128,7 @@ struct nfsnode {
uint32_t n_namelen;
int n_directio_opens;
int n_directio_asyncwr;
struct ucred *n_writecred; /* Cred. for putpages */
};
#define n_atim n_un1.nf_atim