diff options
| author | NeilBrown <neilb@suse.de> | 2016-01-07 22:08:20 +0100 |
|---|---|---|
| committer | Al Viro <viro@zeniv.linux.org.uk> | 2016-01-09 09:07:52 +0100 |
| commit | bbddca8e8fac07ece3938e03526b5d00fa791a4c (patch) | |
| tree | 5fbe9fe5251f1040bb001377260c56f7330e0459 /fs/nfsd/nfs4xdr.c | |
| parent | fs:affs:Replace time_t with time64_t (diff) | |
| download | linux-bbddca8e8fac07ece3938e03526b5d00fa791a4c.tar.xz linux-bbddca8e8fac07ece3938e03526b5d00fa791a4c.zip | |
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: NeilBrown <neilb@suse.de>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs/nfsd/nfs4xdr.c')
| -rw-r--r-- | fs/nfsd/nfs4xdr.c | 8 |
1 files changed, 4 insertions, 4 deletions
diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c index 51c9e9ca39a4..325521ce389a 100644 --- a/fs/nfsd/nfs4xdr.c +++ b/fs/nfsd/nfs4xdr.c @@ -2838,14 +2838,14 @@ 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; |