[PATCH 01/13] VFS: replace {, total_}link_count in task_struct with pointer to nameidata
From: NeilBrown
Date: Mon Mar 16 2015 - 00:44:21 EST
task_struct currently contains two ad-hoc members for use by
the VFS: link_count and total_link_count.
These are only interesting to fs/namei.c, so exposing them
explicitly is poor laying - and has resulted in some questionable
code in staging/lustre.
This patches replaces those with a single pointer to 'struct
nameidata'.
This structure represents the current filename lookup of which
there can only be one per process, and is a natural place to
store link_count and total_link_count.
This will allow the current "nameidata" argument to all
follow_link operations to be removed as current->nameidata
can be used instead.
As there are occasional circumstances where pathname lookup can
recurse, such as through kern_path_locked, we always save and old
current->nameidata (if there is one) when setting a new value, and
make sure any active link_counts are preserved.
Suggested-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: NeilBrown <neilb@xxxxxxx>
---
drivers/staging/lustre/lustre/llite/symlink.c | 16 ++-------
fs/namei.c | 47 +++++++++++++++++++------
include/linux/sched.h | 2 +
3 files changed, 41 insertions(+), 24 deletions(-)
diff --git a/drivers/staging/lustre/lustre/llite/symlink.c b/drivers/staging/lustre/lustre/llite/symlink.c
index 686b6a574cc5..d7a1c6c48846 100644
--- a/drivers/staging/lustre/lustre/llite/symlink.c
+++ b/drivers/staging/lustre/lustre/llite/symlink.c
@@ -126,18 +126,10 @@ static void *ll_follow_link(struct dentry *dentry, struct nameidata *nd)
char *symname = NULL;
CDEBUG(D_VFSTRACE, "VFS Op\n");
- /* Limit the recursive symlink depth to 5 instead of default
- * 8 links when kernel has 4k stack to prevent stack overflow.
- * For 8k stacks we need to limit it to 7 for local servers. */
- if (THREAD_SIZE < 8192 && current->link_count >= 6) {
- rc = -ELOOP;
- } else if (THREAD_SIZE == 8192 && current->link_count >= 8) {
- rc = -ELOOP;
- } else {
- ll_inode_size_lock(inode);
- rc = ll_readlink_internal(inode, &request, &symname);
- ll_inode_size_unlock(inode);
- }
+ ll_inode_size_lock(inode);
+ rc = ll_readlink_internal(inode, &request, &symname);
+ ll_inode_size_unlock(inode);
+
if (rc) {
ptlrpc_req_finished(request);
request = NULL;
diff --git a/fs/namei.c b/fs/namei.c
index c83145af4bfc..184aaafffaa9 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -502,10 +502,27 @@ struct nameidata {
unsigned seq, m_seq;
int last_type;
unsigned depth;
+ int link_count, total_link_count;
struct file *base;
char *saved_names[MAX_NESTED_LINKS + 1];
};
+static struct nameidata *set_nameidata(struct nameidata *p)
+{
+ struct nameidata *old = current->nameidata;
+ current->nameidata = p;
+ if (p) {
+ if (!old) {
+ p->link_count = 0;
+ p->total_link_count = 0;
+ } else {
+ p->link_count = old->link_count;
+ p->total_link_count = old->total_link_count;
+ }
+ }
+ return old;
+}
+
/*
* Path walking has 2 modes, rcu-walk and ref-walk (see
* Documentation/filesystems/path-lookup.txt). In situations when we can't
@@ -863,11 +880,11 @@ follow_link(struct path *link, struct nameidata *nd, void **p)
mntget(link->mnt);
error = -ELOOP;
- if (unlikely(current->total_link_count >= 40))
+ if (unlikely(current->nameidata->total_link_count >= 40))
goto out_put_nd_path;
cond_resched();
- current->total_link_count++;
+ current->nameidata->total_link_count++;
touch_atime(link);
nd_set_link(nd, NULL);
@@ -991,8 +1008,8 @@ static int follow_automount(struct path *path, unsigned flags,
path->dentry->d_inode)
return -EISDIR;
- current->total_link_count++;
- if (current->total_link_count >= 40)
+ current->nameidata->total_link_count++;
+ if (current->nameidata->total_link_count >= 40)
return -ELOOP;
mnt = path->dentry->d_op->d_automount(path);
@@ -1621,7 +1638,7 @@ static inline int nested_symlink(struct path *path, struct nameidata *nd)
{
int res;
- if (unlikely(current->link_count >= MAX_NESTED_LINKS)) {
+ if (unlikely(current->nameidata->link_count >= MAX_NESTED_LINKS)) {
path_put_conditional(path, nd);
path_put(&nd->path);
return -ELOOP;
@@ -1629,7 +1646,7 @@ static inline int nested_symlink(struct path *path, struct nameidata *nd)
BUG_ON(nd->depth >= MAX_NESTED_LINKS);
nd->depth++;
- current->link_count++;
+ current->nameidata->link_count++;
do {
struct path link = *path;
@@ -1642,7 +1659,7 @@ static inline int nested_symlink(struct path *path, struct nameidata *nd)
put_link(nd, &link, cookie);
} while (res > 0);
- current->link_count--;
+ current->nameidata->link_count--;
nd->depth--;
return res;
}
@@ -1948,7 +1965,7 @@ static int path_init(int dfd, const char *name, unsigned int flags,
rcu_read_unlock();
return -ECHILD;
done:
- current->total_link_count = 0;
+ current->nameidata->total_link_count = 0;
return link_path_walk(name, nd);
}
@@ -2027,7 +2044,9 @@ static int path_lookupat(int dfd, const char *name,
static int filename_lookup(int dfd, struct filename *name,
unsigned int flags, struct nameidata *nd)
{
- int retval = path_lookupat(dfd, name->name, flags | LOOKUP_RCU, nd);
+ int retval;
+ struct nameidata *saved_nd = set_nameidata(nd);
+ retval = path_lookupat(dfd, name->name, flags | LOOKUP_RCU, nd);
if (unlikely(retval == -ECHILD))
retval = path_lookupat(dfd, name->name, flags, nd);
if (unlikely(retval == -ESTALE))
@@ -2036,6 +2055,7 @@ static int filename_lookup(int dfd, struct filename *name,
if (likely(!retval))
audit_inode(name, nd->path.dentry, flags & LOOKUP_PARENT);
+ set_nameidata(saved_nd);
return retval;
}
@@ -2343,7 +2363,7 @@ out:
static int
path_mountpoint(int dfd, const char *name, struct path *path, unsigned int flags)
{
- struct nameidata nd;
+ struct nameidata nd, *saved = set_nameidata(&nd);
int err;
err = path_init(dfd, name, flags, &nd);
@@ -2366,6 +2386,7 @@ path_mountpoint(int dfd, const char *name, struct path *path, unsigned int flags
}
out:
path_cleanup(&nd);
+ set_nameidata(saved);
return err;
}
@@ -3217,12 +3238,14 @@ static struct file *path_openat(int dfd, struct filename *pathname,
struct path path;
int opened = 0;
int error;
+ struct nameidata *saved_nd;
file = get_empty_filp();
if (IS_ERR(file))
return file;
file->f_flags = op->open_flag;
+ saved_nd = set_nameidata(nd);
if (unlikely(file->f_flags & __O_TMPFILE)) {
error = do_tmpfile(dfd, pathname, nd, flags, op, file, &opened);
@@ -3269,6 +3292,7 @@ out:
}
file = ERR_PTR(error);
}
+ set_nameidata(saved_nd);
return file;
}
@@ -4429,7 +4453,7 @@ EXPORT_SYMBOL(readlink_copy);
*/
int generic_readlink(struct dentry *dentry, char __user *buffer, int buflen)
{
- struct nameidata nd;
+ struct nameidata nd, *saved = set_nameidata(&nd);
void *cookie;
int res;
@@ -4441,6 +4465,7 @@ int generic_readlink(struct dentry *dentry, char __user *buffer, int buflen)
res = readlink_copy(buffer, buflen, nd_get_link(&nd));
if (dentry->d_inode->i_op->put_link)
dentry->d_inode->i_op->put_link(dentry, &nd, cookie);
+ set_nameidata(saved);
return res;
}
EXPORT_SYMBOL(generic_readlink);
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 6d77432e14ff..b88b9eea169a 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1447,7 +1447,7 @@ struct task_struct {
it with task_lock())
- initialized normally by setup_new_exec */
/* file system info */
- int link_count, total_link_count;
+ struct nameidata *nameidata;
#ifdef CONFIG_SYSVIPC
/* ipc stuff */
struct sysv_sem sysvsem;
--
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