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namei: don't mangle nd->seq in lookup_fast()

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Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2015-05-05 09:40:46 -04:00
parent 6e9918b7b3
commit 254cf58212
1 changed files with 23 additions and 15 deletions
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38
fs/namei.c
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@ -1134,7 +1134,7 @@ static inline int managed_dentry_rcu(struct dentry *dentry)
* we meet a managed dentry that would need blocking. * we meet a managed dentry that would need blocking.
*/ */
static bool __follow_mount_rcu(struct nameidata *nd, struct path *path, static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
struct inode **inode) struct inode **inode, unsigned *seqp)
{ {
for (;;) { for (;;) {
struct mount *mounted; struct mount *mounted;
@ -1161,7 +1161,7 @@ static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
path->mnt = &mounted->mnt; path->mnt = &mounted->mnt;
path->dentry = mounted->mnt.mnt_root; path->dentry = mounted->mnt.mnt_root;
nd->flags |= LOOKUP_JUMPED; 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 * Update the inode too. We don't need to re-check the
* dentry sequence number here after this d_inode read, * 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. * It _is_ time-critical.
*/ */
static int lookup_fast(struct nameidata *nd, 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 vfsmount *mnt = nd->path.mnt;
struct dentry *dentry, *parent = nd->path.dentry; 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)) if (__read_seqcount_retry(&parent->d_seq, nd->seq))
return -ECHILD; return -ECHILD;
nd->seq = seq;
*seqp = seq;
if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE)) { if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE)) {
status = d_revalidate(dentry, nd->flags); status = d_revalidate(dentry, nd->flags);
if (unlikely(status <= 0)) { if (unlikely(status <= 0)) {
@ -1449,10 +1450,10 @@ static int lookup_fast(struct nameidata *nd,
} }
path->mnt = mnt; path->mnt = mnt;
path->dentry = dentry; path->dentry = dentry;
if (likely(__follow_mount_rcu(nd, path, inode))) if (likely(__follow_mount_rcu(nd, path, inode, seqp)))
return 0; return 0;
unlazy: unlazy:
if (unlazy_walk(nd, dentry, nd->seq)) if (unlazy_walk(nd, dentry, seq))
return -ECHILD; return -ECHILD;
} else { } else {
dentry = __d_lookup(parent, &nd->last); dentry = __d_lookup(parent, &nd->last);
@ -1543,7 +1544,7 @@ static void terminate_walk(struct nameidata *nd)
put_link(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; int error;
struct saved *last; struct saved *last;
@ -1553,7 +1554,7 @@ static int pick_link(struct nameidata *nd, struct path *link)
} }
if (nd->flags & LOOKUP_RCU) { if (nd->flags & LOOKUP_RCU) {
if (unlikely(nd->path.mnt != link->mnt || if (unlikely(nd->path.mnt != link->mnt ||
unlazy_walk(nd, link->dentry, nd->seq))) { unlazy_walk(nd, link->dentry, seq))) {
return -ECHILD; 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" * so we keep a cache of "no, this doesn't need follow_link"
* for the common case. * 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))) if (likely(!d_is_symlink(link->dentry)))
return 0; return 0;
if (!follow) if (!follow)
return 0; return 0;
return pick_link(nd, link); return pick_link(nd, link, seq);
} }
enum {WALK_GET = 1, WALK_PUT = 2}; enum {WALK_GET = 1, WALK_PUT = 2};
@ -1592,6 +1594,7 @@ static int walk_component(struct nameidata *nd, int flags)
{ {
struct path path; struct path path;
struct inode *inode; struct inode *inode;
unsigned seq;
int err; int err;
/* /*
* "." and ".." are special - ".." especially so because it has * "." and ".." are special - ".." especially so because it has
@ -1604,7 +1607,7 @@ static int walk_component(struct nameidata *nd, int flags)
put_link(nd); put_link(nd);
return err; return err;
} }
err = lookup_fast(nd, &path, &inode); err = lookup_fast(nd, &path, &inode, &seq);
if (unlikely(err)) { if (unlikely(err)) {
if (err < 0) if (err < 0)
return err; return err;
@ -1614,6 +1617,7 @@ static int walk_component(struct nameidata *nd, int flags)
return err; return err;
inode = path.dentry->d_inode; inode = path.dentry->d_inode;
seq = 0; /* we are already out of RCU mode */
err = -ENOENT; err = -ENOENT;
if (d_is_negative(path.dentry)) if (d_is_negative(path.dentry))
goto out_path_put; goto out_path_put;
@ -1621,11 +1625,12 @@ static int walk_component(struct nameidata *nd, int flags)
if (flags & WALK_PUT) if (flags & WALK_PUT)
put_link(nd); 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)) if (unlikely(err))
return err; return err;
path_to_nameidata(&path, nd); path_to_nameidata(&path, nd);
nd->inode = inode; nd->inode = inode;
nd->seq = seq;
return 0; return 0;
out_path_put: out_path_put:
@ -2342,7 +2347,7 @@ done:
put_link(nd); put_link(nd);
path->dentry = dentry; path->dentry = dentry;
path->mnt = nd->path.mnt; 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)) if (unlikely(error))
return error; return error;
mntget(path->mnt); mntget(path->mnt);
@ -2939,6 +2944,7 @@ static int do_last(struct nameidata *nd,
bool will_truncate = (open_flag & O_TRUNC) != 0; bool will_truncate = (open_flag & O_TRUNC) != 0;
bool got_write = false; bool got_write = false;
int acc_mode = op->acc_mode; int acc_mode = op->acc_mode;
unsigned seq;
struct inode *inode; struct inode *inode;
struct path save_parent = { .dentry = NULL, .mnt = NULL }; struct path save_parent = { .dentry = NULL, .mnt = NULL };
struct path path; struct path path;
@ -2959,7 +2965,7 @@ static int do_last(struct nameidata *nd,
if (nd->last.name[nd->last.len]) if (nd->last.name[nd->last.len])
nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY; nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
/* we _can_ be in RCU mode here */ /* we _can_ be in RCU mode here */
error = lookup_fast(nd, &path, &inode); error = lookup_fast(nd, &path, &inode, &seq);
if (likely(!error)) if (likely(!error))
goto finish_lookup; goto finish_lookup;
@ -3047,6 +3053,7 @@ retry_lookup:
BUG_ON(nd->flags & LOOKUP_RCU); BUG_ON(nd->flags & LOOKUP_RCU);
inode = path.dentry->d_inode; inode = path.dentry->d_inode;
seq = 0; /* out of RCU mode, so the value doesn't matter */
if (unlikely(d_is_negative(path.dentry))) { if (unlikely(d_is_negative(path.dentry))) {
path_to_nameidata(&path, nd); path_to_nameidata(&path, nd);
return -ENOENT; return -ENOENT;
@ -3054,7 +3061,7 @@ retry_lookup:
finish_lookup: finish_lookup:
if (nd->depth) if (nd->depth)
put_link(nd); 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)) if (unlikely(error))
return error; return error;
@ -3072,6 +3079,7 @@ finish_lookup:
} }
nd->inode = inode; nd->inode = inode;
nd->seq = seq;
/* Why this, you ask? _Now_ we might have grown LOOKUP_JUMPED... */ /* Why this, you ask? _Now_ we might have grown LOOKUP_JUMPED... */
finish_open: finish_open:
error = complete_walk(nd); error = complete_walk(nd);