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authorNeilBrown <neilb@suse.de>2016-01-07 16:08:20 -0500
committerAl Viro <viro@zeniv.linux.org.uk>2016-01-09 03:07:52 -0500
commitbbddca8e8fac07ece3938e03526b5d00fa791a4c (patch)
tree5fbe9fe5251f1040bb001377260c56f7330e0459 /include/linux/namei.h
parentdb39c16724d019029d7533561754d92bef1b389a (diff)
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op-kernel-dev-bbddca8e8fac07ece3938e03526b5d00fa791a4c.tar.gz
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 'include/linux/namei.h')
-rw-r--r--include/linux/namei.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/namei.h b/include/linux/namei.h
index d8c6334..d0f25d8 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -77,6 +77,7 @@ 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 *);
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