From 4675ac39b5dd5ff08dd8cb2be9ddd3cba778aa39 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Mon, 9 Jan 2017 22:29:15 -0500 Subject: namei.c: split unlazy_walk() In all but one case, the last two arguments are NULL and 0 resp.; almost everyone just wants to switch nameidata to non-RCU mode. The only exception is lookup_fast(), where we have a child dentry we want to legitimize as well. Split these two cases. Signed-off-by: Al Viro --- fs/namei.c | 105 ++++++++++++++++++++++++++++++++++++++----------------------- 1 file changed, 66 insertions(+), 39 deletions(-) (limited to 'fs/namei.c') diff --git a/fs/namei.c b/fs/namei.c index 2ed2701a74b5..76cfeb641e97 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -672,52 +672,83 @@ static bool legitimize_links(struct nameidata *nd) /** * unlazy_walk - try to switch to ref-walk mode. * @nd: nameidata pathwalk data - * @dentry: child of nd->path.dentry or NULL - * @seq: seq number to check dentry against * Returns: 0 on success, -ECHILD on failure * - * unlazy_walk attempts to legitimize the current nd->path, nd->root and dentry - * for ref-walk mode. @dentry must be a path found by a do_lookup call on - * @nd or NULL. Must be called from rcu-walk context. + * unlazy_walk attempts to legitimize the current nd->path and nd->root + * for ref-walk mode. + * Must be called from rcu-walk context. * Nothing should touch nameidata between unlazy_walk() failure and * terminate_walk(). */ -static int unlazy_walk(struct nameidata *nd, struct dentry *dentry, unsigned seq) +static int unlazy_walk(struct nameidata *nd) { struct dentry *parent = nd->path.dentry; BUG_ON(!(nd->flags & LOOKUP_RCU)); + nd->flags &= ~LOOKUP_RCU; + if (unlikely(!legitimize_links(nd))) + goto out2; + if (unlikely(!legitimize_path(nd, &nd->path, nd->seq))) + goto out1; + if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) { + if (unlikely(!legitimize_path(nd, &nd->root, nd->root_seq))) + goto out; + } + rcu_read_unlock(); + BUG_ON(nd->inode != parent->d_inode); + return 0; + +out2: + nd->path.mnt = NULL; + nd->path.dentry = NULL; +out1: + if (!(nd->flags & LOOKUP_ROOT)) + nd->root.mnt = NULL; +out: + rcu_read_unlock(); + return -ECHILD; +} + +/** + * unlazy_child - try to switch to ref-walk mode. + * @nd: nameidata pathwalk data + * @dentry: child of nd->path.dentry + * @seq: seq number to check dentry against + * Returns: 0 on success, -ECHILD on failure + * + * unlazy_child attempts to legitimize the current nd->path, nd->root and dentry + * for ref-walk mode. @dentry must be a path found by a do_lookup call on + * @nd. Must be called from rcu-walk context. + * Nothing should touch nameidata between unlazy_child() failure and + * terminate_walk(). + */ +static int unlazy_child(struct nameidata *nd, struct dentry *dentry, unsigned seq) +{ + BUG_ON(!(nd->flags & LOOKUP_RCU)); + nd->flags &= ~LOOKUP_RCU; if (unlikely(!legitimize_links(nd))) goto out2; if (unlikely(!legitimize_mnt(nd->path.mnt, nd->m_seq))) goto out2; - if (unlikely(!lockref_get_not_dead(&parent->d_lockref))) + if (unlikely(!lockref_get_not_dead(&nd->path.dentry->d_lockref))) goto out1; /* - * For a negative lookup, the lookup sequence point is the parents - * sequence point, and it only needs to revalidate the parent dentry. - * - * For a positive lookup, we need to move both the parent and the - * dentry from the RCU domain to be properly refcounted. And the - * sequence number in the dentry validates *both* dentry counters, - * since we checked the sequence number of the parent after we got - * the child sequence number. So we know the parent must still - * be valid if the child sequence number is still valid. + * We need to move both the parent and the dentry from the RCU domain + * to be properly refcounted. And the sequence number in the dentry + * validates *both* dentry counters, since we checked the sequence + * number of the parent after we got the child sequence number. So we + * know the parent must still be valid if the child sequence number is */ - if (!dentry) { - if (read_seqcount_retry(&parent->d_seq, nd->seq)) - goto out; - BUG_ON(nd->inode != parent->d_inode); - } else { - if (!lockref_get_not_dead(&dentry->d_lockref)) - goto out; - if (read_seqcount_retry(&dentry->d_seq, seq)) - goto drop_dentry; + if (unlikely(!lockref_get_not_dead(&dentry->d_lockref))) + goto out; + if (unlikely(read_seqcount_retry(&dentry->d_seq, seq))) { + rcu_read_unlock(); + dput(dentry); + goto drop_root_mnt; } - /* * Sequence counts matched. Now make sure that the root is * still valid and get it if required. @@ -733,10 +764,6 @@ static int unlazy_walk(struct nameidata *nd, struct dentry *dentry, unsigned seq rcu_read_unlock(); return 0; -drop_dentry: - rcu_read_unlock(); - dput(dentry); - goto drop_root_mnt; out2: nd->path.mnt = NULL; out1: @@ -775,7 +802,7 @@ static int complete_walk(struct nameidata *nd) if (nd->flags & LOOKUP_RCU) { if (!(nd->flags & LOOKUP_ROOT)) nd->root.mnt = NULL; - if (unlikely(unlazy_walk(nd, NULL, 0))) + if (unlikely(unlazy_walk(nd))) return -ECHILD; } @@ -1001,7 +1028,7 @@ const char *get_link(struct nameidata *nd) touch_atime(&last->link); cond_resched(); } else if (atime_needs_update_rcu(&last->link, inode)) { - if (unlikely(unlazy_walk(nd, NULL, 0))) + if (unlikely(unlazy_walk(nd))) return ERR_PTR(-ECHILD); touch_atime(&last->link); } @@ -1020,7 +1047,7 @@ const char *get_link(struct nameidata *nd) if (nd->flags & LOOKUP_RCU) { res = get(NULL, inode, &last->done); if (res == ERR_PTR(-ECHILD)) { - if (unlikely(unlazy_walk(nd, NULL, 0))) + if (unlikely(unlazy_walk(nd))) return ERR_PTR(-ECHILD); res = get(dentry, inode, &last->done); } @@ -1529,7 +1556,7 @@ static int lookup_fast(struct nameidata *nd, bool negative; dentry = __d_lookup_rcu(parent, &nd->last, &seq); if (unlikely(!dentry)) { - if (unlazy_walk(nd, NULL, 0)) + if (unlazy_walk(nd)) return -ECHILD; return 0; } @@ -1567,7 +1594,7 @@ static int lookup_fast(struct nameidata *nd, if (likely(__follow_mount_rcu(nd, path, inode, seqp))) return 1; } - if (unlazy_walk(nd, dentry, seq)) + if (unlazy_child(nd, dentry, seq)) return -ECHILD; if (unlikely(status == -ECHILD)) /* we'd been told to redo it in non-rcu mode */ @@ -1646,7 +1673,7 @@ static inline int may_lookup(struct nameidata *nd) int err = inode_permission(nd->inode, MAY_EXEC|MAY_NOT_BLOCK); if (err != -ECHILD) return err; - if (unlazy_walk(nd, NULL, 0)) + if (unlazy_walk(nd)) return -ECHILD; } return inode_permission(nd->inode, MAY_EXEC); @@ -1690,7 +1717,7 @@ static int pick_link(struct nameidata *nd, struct path *link, if (!(nd->flags & LOOKUP_ROOT)) nd->root.mnt = NULL; rcu_read_unlock(); - } else if (likely(unlazy_walk(nd, NULL, 0)) == 0) + } else if (likely(unlazy_walk(nd)) == 0) error = nd_alloc_stack(nd); } if (error) { @@ -2108,7 +2135,7 @@ OK: } if (unlikely(!d_can_lookup(nd->path.dentry))) { if (nd->flags & LOOKUP_RCU) { - if (unlazy_walk(nd, NULL, 0)) + if (unlazy_walk(nd)) return -ECHILD; } return -ENOTDIR; @@ -2565,7 +2592,7 @@ mountpoint_last(struct nameidata *nd) /* If we're in rcuwalk, drop out of it to handle last component */ if (nd->flags & LOOKUP_RCU) { - if (unlazy_walk(nd, NULL, 0)) + if (unlazy_walk(nd)) return -ECHILD; } -- cgit v1.2.3-55-g7522