On Tue, May 05, 2015 at 10:18:01AM -0400, J. Bruce Fields wrote:
> On Tue, May 05, 2015 at 09:54:43PM +0800, Kinglong Mee wrote:
> > On 5/5/2015 6:01 AM, J. Bruce Fields wrote:
> > > + * Unlike lookup_one_len, it should be called without the parent
> > > + * i_mutex held, and will take the i_mutex itself if necessary.
> > > + */
> > > +struct dentry *lookup_one_len_unlocked(const char *name,
> > > + struct dentry *base, int len)
> > > +{
> > > + struct qstr this;
> > > + unsigned int c;
> > > + int err;
> > > + struct dentry *ret;
> > > +
> > > + WARN_ON_ONCE(!mutex_is_locked(&base->d_inode->i_mutex));
> >
> > Remove this line.
>
> Whoops, thanks.
>
> > > diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
> > > index a30e79900086..cc7995762190 100644
> > > --- a/fs/nfsd/vfs.c
> > > +++ b/fs/nfsd/vfs.c
> > > @@ -217,6 +217,13 @@ nfsd_lookup_dentry(struct svc_rqst *rqstp, struct svc_fh *fhp,
> > > host_err = PTR_ERR(dentry);
> > > if (IS_ERR(dentry))
> > > goto out_nfserr;
> > > + if (!S_ISREG(d_inode(dentry)->i_mode)) {
> >
> > Got a crash here tested by pynfs,
>
> OK, I guess I just forgot to take into account negative dentries.
> Testing that now with (!(d_inode(dentry) && S_ISREG(..))).
And I also forgot nfs3xdr.c.
--b.
commit 6c942d342f9f
Author: NeilBrown <neilb@xxxxxxx>
Date: Fri May 1 11:53:26 2015 +1000
nfsd: don't hold i_mutex over userspace upcalls
We need information about exports when crossing mountpoints during
lookup or NFSv4 readdir. If we don't already have that information
cached, we may have to ask (and wait for) rpc.mountd.
In both cases we currently hold the i_mutex on the parent of the
directory we're asking rpc.mountd about. We've seen situations where
rpc.mountd performs some operation on that directory that tries to take
the i_mutex again, resulting in deadlock.
With some care, we may be able to avoid that in rpc.mountd. But it
seems better just to avoid holding a mutex while waiting on userspace.
It appears that lookup_one_len is pretty much the only operation that
needs the i_mutex. So we could just drop the i_mutex elsewhere and do
something like
mutex_lock()
lookup_one_len()
mutex_unlock()
In many cases though the lookup would have been cached and not required
the i_mutex, so it's more efficient to create a lookup_one_len() variant
that only takes the i_mutex when necessary.
Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
diff --git a/fs/namei.c b/fs/namei.c
index 4a8d998b7274..0f554bf41dea 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2139,6 +2139,8 @@ static struct dentry *lookup_hash(struct nameidata *nd)
*
* Note that this routine is purely a helper for filesystem usage and should
* not be called by generic code.
+ *
+ * Must be called with the parented i_mutex held.
*/
struct dentry *lookup_one_len(const char *name, struct dentry *base, int len)
{
@@ -2182,6 +2184,66 @@ struct dentry *lookup_one_len(const char *name, struct dentry *base, int len)
}
EXPORT_SYMBOL(lookup_one_len);
+/**
+ * lookup_one_len - filesystem helper to lookup single pathname component
+ * @name: pathname component to lookup
+ * @base: base directory to lookup from
+ * @len: maximum length @len should be interpreted to
+ *
+ * Note that this routine is purely a helper for filesystem usage and should
+ * not be called by generic code.
+ *
+ * Unlike lookup_one_len, it should be called without the parent
+ * i_mutex held, and will take the i_mutex itself if necessary.
+ */
+struct dentry *lookup_one_len_unlocked(const char *name,
+ struct dentry *base, int len)
+{
+ struct qstr this;
+ unsigned int c;
+ int err;
+ struct dentry *ret;
+
+ this.name = name;
+ this.len = len;
+ this.hash = full_name_hash(name, len);
+ if (!len)
+ return ERR_PTR(-EACCES);
+
+ if (unlikely(name[0] == '.')) {
+ if (len < 2 || (len == 2 && name[1] == '.'))
+ return ERR_PTR(-EACCES);
+ }
+
+ while (len--) {
+ c = *(const unsigned char *)name++;
+ if (c == '/' || c == '\0')
+ return ERR_PTR(-EACCES);
+ }
+ /*
+ * See if the low-level filesystem might want
+ * to use its own hash..
+ */
+ if (base->d_flags & DCACHE_OP_HASH) {
+ int err = base->d_op->d_hash(base, &this);
+ if (err < 0)
+ return ERR_PTR(err);
+ }
+
+ err = inode_permission(base->d_inode, MAY_EXEC);
+ if (err)
+ return ERR_PTR(err);
+
+ ret = __d_lookup(base, &this);
+ if (ret)
+ return ret;
+ mutex_lock(&base->d_inode->i_mutex);
+ ret = __lookup_hash(&this, base, 0);
+ mutex_unlock(&base->d_inode->i_mutex);
+ return ret;
+}
+EXPORT_SYMBOL(lookup_one_len_unlocked);
+
int user_path_at_empty(int dfd, const char __user *name, unsigned flags,
struct path *path, int *empty)
{
diff --git a/fs/nfsd/nfs3xdr.c b/fs/nfsd/nfs3xdr.c
index f6e7cbabac5a..01dcd494f781 100644
--- a/fs/nfsd/nfs3xdr.c
+++ b/fs/nfsd/nfs3xdr.c
@@ -823,7 +823,7 @@ compose_entry_fh(struct nfsd3_readdirres *cd, struct svc_fh *fhp,
} else
dchild = dget(dparent);
} else
- dchild = lookup_one_len(name, dparent, namlen);
+ dchild = lookup_one_len_unlocked(name, dparent, namlen);
if (IS_ERR(dchild))
return rv;
if (d_mountpoint(dchild))
diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index 158badf945df..2c1adaa0bd2f 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -2804,14 +2804,14 @@ nfsd4_encode_dirent_fattr(struct xdr_stream *xdr, struct nfsd4_readdir *cd,
__be32 nfserr;
int ignore_crossmnt = 0;
- dentry = lookup_one_len(name, cd->rd_fhp->fh_dentry, namlen);
+ dentry = lookup_one_len_unlocked(name, cd->rd_fhp->fh_dentry, namlen);
if (IS_ERR(dentry))
return nfserrno(PTR_ERR(dentry));
if (d_really_is_negative(dentry)) {
/*
- * nfsd_buffered_readdir drops the i_mutex between
- * readdir and calling this callback, leaving a window
- * where this directory entry could have gone away.
+ * we're not holding the i_mutex here, so there's
+ * a window where this directory entry could have gone
+ * away.
*/
dput(dentry);
return nfserr_noent;
diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index a30e79900086..4accdb00976b 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -217,6 +217,13 @@ nfsd_lookup_dentry(struct svc_rqst *rqstp, struct svc_fh *fhp,
host_err = PTR_ERR(dentry);
if (IS_ERR(dentry))
goto out_nfserr;
+ if (!(d_inode(dentry) && S_ISREG(d_inode(dentry)->i_mode))) {
+ /*
+ * Never mind, we're not going to open this
+ * anyway. And we don't want to hold it over
+ * the userspace upcalls in nfsd_mountpoint. */
+ fh_unlock(fhp);
+ }
/*
* check if we have crossed a mount point ...
*/
@@ -1876,7 +1883,6 @@ static __be32 nfsd_buffered_readdir(struct file *file, nfsd_filldir_t func,
offset = *offsetp;
while (1) {
- struct inode *dir_inode = file_inode(file);
unsigned int reclen;
cdp->err = nfserr_eof; /* will be cleared on successful read */
@@ -1895,15 +1901,6 @@ static __be32 nfsd_buffered_readdir(struct file *file, nfsd_filldir_t func,
if (!size)
break;
- /*
- * Various filldir functions may end up calling back into
- * lookup_one_len() and the file system's ->lookup() method.
- * These expect i_mutex to be held, as it would within readdir.
- */
- host_err = mutex_lock_killable(&dir_inode->i_mutex);
- if (host_err)
- break;
-
de = (struct buffered_dirent *)buf.dirent;
while (size > 0) {
offset = de->offset;
@@ -1920,7 +1917,6 @@ static __be32 nfsd_buffered_readdir(struct file *file, nfsd_filldir_t func,
size -= reclen;
de = (struct buffered_dirent *)((char *)de + reclen);
}
- mutex_unlock(&dir_inode->i_mutex);
if (size > 0) /* We bailed out early */
break;
diff --git a/include/linux/namei.h b/include/linux/namei.h
index c8990779f0c3..bb3a2f7cca67 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -62,6 +62,7 @@ extern struct dentry *kern_path_locked(const char *, struct path *);
extern int kern_path_mountpoint(int, const char *, struct path *, unsigned int);
extern struct dentry *lookup_one_len(const char *, struct dentry *, int);
+extern struct dentry *lookup_one_len_unlocked(const char *, struct dentry *, int);
extern int follow_down_one(struct path *);
extern int follow_down(struct path *);
--
To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
