From d41efb522e902364ab09c782d511c1bedc388ddd Mon Sep 17 00:00:00 2001 From: Al Viro Date: Mon, 4 Nov 2019 22:30:52 -0500 Subject: fs/namei.c: pull positivity check into follow_managed() There are 4 callers; two proceed to check if result is positive and fail with ENOENT if it isn't; one (in handle_lookup_down()) is guaranteed to yield positive and one (in lookup_fast()) is _preceded_ by positivity check. However, follow_managed() on a negative dentry is a (fairly cheap) no-op on anything other than autofs. And negative autofs dentries are never hashed, so lookup_fast() is not going to run into one of those. Moreover, successful follow_managed() on a _positive_ dentry never yields a negative one (and we significantly rely upon that in callers of lookup_fast()). In other words, we can easily transpose the positivity check and the call of follow_managed() in lookup_fast(). And that allows to fold the positivity check *into* follow_managed(), simplifying life for the code downstream of its calls. Signed-off-by: Al Viro --- fs/namei.c | 34 +++++++++++----------------------- include/linux/dcache.h | 5 +++++ 2 files changed, 16 insertions(+), 23 deletions(-) diff --git a/fs/namei.c b/fs/namei.c index 671c3c1a3425..ef55155d152f 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -1206,25 +1206,25 @@ static int follow_automount(struct path *path, struct nameidata *nd, * - Flagged as automount point * * This may only be called in refwalk mode. + * On success path->dentry is known positive. * * Serialization is taken care of in namespace.c */ static int follow_managed(struct path *path, struct nameidata *nd) { struct vfsmount *mnt = path->mnt; /* held by caller, must be left alone */ - unsigned managed; + unsigned flags; bool need_mntput = false; int ret = 0; /* Given that we're not holding a lock here, we retain the value in a * local variable for each dentry as we look at it so that we don't see * the components of that value change under us */ - while (managed = READ_ONCE(path->dentry->d_flags), - managed &= DCACHE_MANAGED_DENTRY, - unlikely(managed != 0)) { + while (flags = READ_ONCE(path->dentry->d_flags), + unlikely(flags & DCACHE_MANAGED_DENTRY)) { /* Allow the filesystem to manage the transit without i_mutex * being held. */ - if (managed & DCACHE_MANAGE_TRANSIT) { + if (flags & DCACHE_MANAGE_TRANSIT) { BUG_ON(!path->dentry->d_op); BUG_ON(!path->dentry->d_op->d_manage); ret = path->dentry->d_op->d_manage(path, false); @@ -1233,7 +1233,7 @@ static int follow_managed(struct path *path, struct nameidata *nd) } /* Transit to a mounted filesystem. */ - if (managed & DCACHE_MOUNTED) { + if (flags & DCACHE_MOUNTED) { struct vfsmount *mounted = lookup_mnt(path); if (mounted) { dput(path->dentry); @@ -1252,7 +1252,7 @@ static int follow_managed(struct path *path, struct nameidata *nd) } /* Handle an automount point */ - if (managed & DCACHE_NEED_AUTOMOUNT) { + if (flags & DCACHE_NEED_AUTOMOUNT) { ret = follow_automount(path, nd, &need_mntput); if (ret < 0) break; @@ -1265,10 +1265,12 @@ static int follow_managed(struct path *path, struct nameidata *nd) if (need_mntput && path->mnt == mnt) mntput(path->mnt); - if (ret == -EISDIR || !ret) - ret = 1; if (need_mntput) nd->flags |= LOOKUP_JUMPED; + if (ret == -EISDIR || !ret) + ret = 1; + if (ret > 0 && unlikely(d_flags_negative(flags))) + ret = -ENOENT; if (unlikely(ret < 0)) path_put_conditional(path, nd); return ret; @@ -1617,10 +1619,6 @@ static int lookup_fast(struct nameidata *nd, dput(dentry); return status; } - if (unlikely(d_is_negative(dentry))) { - dput(dentry); - return -ENOENT; - } path->mnt = mnt; path->dentry = dentry; @@ -1807,11 +1805,6 @@ static int walk_component(struct nameidata *nd, int flags) if (unlikely(err < 0)) return err; - if (unlikely(d_is_negative(path.dentry))) { - path_to_nameidata(&path, nd); - return -ENOENT; - } - seq = 0; /* we are already out of RCU mode */ inode = d_backing_inode(path.dentry); } @@ -3352,11 +3345,6 @@ static int do_last(struct nameidata *nd, if (unlikely(error < 0)) return error; - if (unlikely(d_is_negative(path.dentry))) { - path_to_nameidata(&path, nd); - return -ENOENT; - } - /* * create/update audit record if it already exists. */ diff --git a/include/linux/dcache.h b/include/linux/dcache.h index 10090f11ab95..c1488cc84fd9 100644 --- a/include/linux/dcache.h +++ b/include/linux/dcache.h @@ -440,6 +440,11 @@ static inline bool d_is_negative(const struct dentry *dentry) return d_is_miss(dentry); } +static inline bool d_flags_negative(unsigned flags) +{ + return (flags & DCACHE_ENTRY_TYPE) == DCACHE_MISS_TYPE; +} + static inline bool d_is_positive(const struct dentry *dentry) { return !d_is_negative(dentry); -- cgit v1.2.3