From 254cf582127b200ea6d4e55c9b4965485c3fe4c8 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Tue, 5 May 2015 09:40:46 -0400 Subject: [PATCH] namei: don't mangle nd->seq in lookup_fast() Signed-off-by: Al Viro --- fs/namei.c | 38 +++++++++++++++++++++++--------------- 1 file changed, 23 insertions(+), 15 deletions(-) diff --git a/fs/namei.c b/fs/namei.c index 97315dfcf464..e3214506016d 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -1134,7 +1134,7 @@ static inline int managed_dentry_rcu(struct dentry *dentry) * we meet a managed dentry that would need blocking. */ static bool __follow_mount_rcu(struct nameidata *nd, struct path *path, - struct inode **inode) + struct inode **inode, unsigned *seqp) { for (;;) { struct mount *mounted; @@ -1161,7 +1161,7 @@ static bool __follow_mount_rcu(struct nameidata *nd, struct path *path, path->mnt = &mounted->mnt; path->dentry = mounted->mnt.mnt_root; nd->flags |= LOOKUP_JUMPED; - nd->seq = read_seqcount_begin(&path->dentry->d_seq); + *seqp = read_seqcount_begin(&path->dentry->d_seq); /* * Update the inode too. We don't need to re-check the * dentry sequence number here after this d_inode read, @@ -1397,7 +1397,8 @@ static struct dentry *__lookup_hash(struct qstr *name, * It _is_ time-critical. */ static int lookup_fast(struct nameidata *nd, - struct path *path, struct inode **inode) + struct path *path, struct inode **inode, + unsigned *seqp) { struct vfsmount *mnt = nd->path.mnt; struct dentry *dentry, *parent = nd->path.dentry; @@ -1437,8 +1438,8 @@ static int lookup_fast(struct nameidata *nd, */ if (__read_seqcount_retry(&parent->d_seq, nd->seq)) return -ECHILD; - nd->seq = seq; + *seqp = seq; if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE)) { status = d_revalidate(dentry, nd->flags); if (unlikely(status <= 0)) { @@ -1449,10 +1450,10 @@ static int lookup_fast(struct nameidata *nd, } path->mnt = mnt; path->dentry = dentry; - if (likely(__follow_mount_rcu(nd, path, inode))) + if (likely(__follow_mount_rcu(nd, path, inode, seqp))) return 0; unlazy: - if (unlazy_walk(nd, dentry, nd->seq)) + if (unlazy_walk(nd, dentry, seq)) return -ECHILD; } else { dentry = __d_lookup(parent, &nd->last); @@ -1543,7 +1544,7 @@ static void terminate_walk(struct nameidata *nd) put_link(nd); } -static int pick_link(struct nameidata *nd, struct path *link) +static int pick_link(struct nameidata *nd, struct path *link, unsigned seq) { int error; struct saved *last; @@ -1553,7 +1554,7 @@ static int pick_link(struct nameidata *nd, struct path *link) } if (nd->flags & LOOKUP_RCU) { if (unlikely(nd->path.mnt != link->mnt || - unlazy_walk(nd, link->dentry, nd->seq))) { + unlazy_walk(nd, link->dentry, seq))) { return -ECHILD; } } @@ -1577,13 +1578,14 @@ static int pick_link(struct nameidata *nd, struct path *link) * so we keep a cache of "no, this doesn't need follow_link" * for the common case. */ -static inline int should_follow_link(struct nameidata *nd, struct path *link, int follow) +static inline int should_follow_link(struct nameidata *nd, struct path *link, + int follow, unsigned seq) { if (likely(!d_is_symlink(link->dentry))) return 0; if (!follow) return 0; - return pick_link(nd, link); + return pick_link(nd, link, seq); } enum {WALK_GET = 1, WALK_PUT = 2}; @@ -1592,6 +1594,7 @@ static int walk_component(struct nameidata *nd, int flags) { struct path path; struct inode *inode; + unsigned seq; int err; /* * "." and ".." are special - ".." especially so because it has @@ -1604,7 +1607,7 @@ static int walk_component(struct nameidata *nd, int flags) put_link(nd); return err; } - err = lookup_fast(nd, &path, &inode); + err = lookup_fast(nd, &path, &inode, &seq); if (unlikely(err)) { if (err < 0) return err; @@ -1614,6 +1617,7 @@ static int walk_component(struct nameidata *nd, int flags) return err; inode = path.dentry->d_inode; + seq = 0; /* we are already out of RCU mode */ err = -ENOENT; if (d_is_negative(path.dentry)) goto out_path_put; @@ -1621,11 +1625,12 @@ static int walk_component(struct nameidata *nd, int flags) if (flags & WALK_PUT) put_link(nd); - err = should_follow_link(nd, &path, flags & WALK_GET); + err = should_follow_link(nd, &path, flags & WALK_GET, seq); if (unlikely(err)) return err; path_to_nameidata(&path, nd); nd->inode = inode; + nd->seq = seq; return 0; out_path_put: @@ -2342,7 +2347,7 @@ done: put_link(nd); path->dentry = dentry; path->mnt = nd->path.mnt; - error = should_follow_link(nd, path, nd->flags & LOOKUP_FOLLOW); + error = should_follow_link(nd, path, nd->flags & LOOKUP_FOLLOW, 0); if (unlikely(error)) return error; mntget(path->mnt); @@ -2939,6 +2944,7 @@ static int do_last(struct nameidata *nd, bool will_truncate = (open_flag & O_TRUNC) != 0; bool got_write = false; int acc_mode = op->acc_mode; + unsigned seq; struct inode *inode; struct path save_parent = { .dentry = NULL, .mnt = NULL }; struct path path; @@ -2959,7 +2965,7 @@ static int do_last(struct nameidata *nd, if (nd->last.name[nd->last.len]) nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY; /* we _can_ be in RCU mode here */ - error = lookup_fast(nd, &path, &inode); + error = lookup_fast(nd, &path, &inode, &seq); if (likely(!error)) goto finish_lookup; @@ -3047,6 +3053,7 @@ retry_lookup: BUG_ON(nd->flags & LOOKUP_RCU); inode = path.dentry->d_inode; + seq = 0; /* out of RCU mode, so the value doesn't matter */ if (unlikely(d_is_negative(path.dentry))) { path_to_nameidata(&path, nd); return -ENOENT; @@ -3054,7 +3061,7 @@ retry_lookup: finish_lookup: if (nd->depth) put_link(nd); - error = should_follow_link(nd, &path, nd->flags & LOOKUP_FOLLOW); + error = should_follow_link(nd, &path, nd->flags & LOOKUP_FOLLOW, seq); if (unlikely(error)) return error; @@ -3072,6 +3079,7 @@ finish_lookup: } nd->inode = inode; + nd->seq = seq; /* Why this, you ask? _Now_ we might have grown LOOKUP_JUMPED... */ finish_open: error = complete_walk(nd); -- 2.30.2