[PATCH v3 093/110] namei: don't mangle nd->seq in lookup_fast()
From: Al Viro
Date: Mon May 11 2015 - 14:14:44 EST
From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
---
fs/namei.c | 38 +++++++++++++++++++++++---------------
1 file changed, 23 insertions(+), 15 deletions(-)
diff --git a/fs/namei.c b/fs/namei.c
index 97315df..e321450 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);
--
2.1.4
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