linux-kernel - Re: [PATCH] cgroups: remove some redundant NULL checks

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Message-ID: <492643E3.8090906@cn.fujitsu.com>
Date:	Fri, 21 Nov 2008 13:15:15 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Linux Containers <containers@...ts.linux-foundation.org>,
	Paul Menage <menage@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cgroups: remove some redundant NULL checks

- In cgroup_clone(), if vfs_mkdir() returns successfully,
  dentry->d_fsdata will be the pointer to the newly created
  cgroup and won't be NULL.

- a cgroup file's dentry->d_fsdata won't be NULL, guaranteed
  by cgroup_add_file().

- When walking through the subsystems of a cgroup_fs (using
  for_each_subsys), cgrp->subsys[ss->subsys_id] won't be NULL,
  guaranteed by cgroup_create().

(Also remove 2 unused variables in cgroup_rmdir().

Signed-off-by: Li Zefan <lizf@...fujitsu.com>
---

There was a compile warning..resend this patch. Sorry for bothering.

---
 kernel/cgroup.c |   29 +++++++----------------------
 1 files changed, 7 insertions(+), 22 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index fe00b3b..7b0e4a5 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -588,7 +588,7 @@ static void cgroup_call_pre_destroy(struct cgroup *cgrp)
 {
 	struct cgroup_subsys *ss;
 	for_each_subsys(cgrp->root, ss)
-		if (ss->pre_destroy && cgrp->subsys[ss->subsys_id])
+		if (ss->pre_destroy)
 			ss->pre_destroy(ss, cgrp);
 	return;
 }
@@ -612,10 +612,8 @@ static void cgroup_diput(struct dentry *dentry, struct inode *inode)
 		/*
 		 * Release the subsystem state objects.
 		 */
-		for_each_subsys(cgrp->root, ss) {
-			if (cgrp->subsys[ss->subsys_id])
-				ss->destroy(ss, cgrp);
-		}
+		for_each_subsys(cgrp->root, ss)
+			ss->destroy(ss, cgrp);
 
 		cgrp->root->number_of_cgroups--;
 		mutex_unlock(&cgroup_mutex);
@@ -1443,7 +1441,7 @@ static ssize_t cgroup_file_write(struct file *file, const char __user *buf,
 	struct cftype *cft = __d_cft(file->f_dentry);
 	struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
 
-	if (!cft || cgroup_is_removed(cgrp))
+	if (cgroup_is_removed(cgrp))
 		return -ENODEV;
 	if (cft->write)
 		return cft->write(cgrp, cft, file, buf, nbytes, ppos);
@@ -1488,7 +1486,7 @@ static ssize_t cgroup_file_read(struct file *file, char __user *buf,
 	struct cftype *cft = __d_cft(file->f_dentry);
 	struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
 
-	if (!cft || cgroup_is_removed(cgrp))
+	if (cgroup_is_removed(cgrp))
 		return -ENODEV;
 
 	if (cft->read)
@@ -1552,10 +1550,8 @@ static int cgroup_file_open(struct inode *inode, struct file *file)
 	err = generic_file_open(inode, file);
 	if (err)
 		return err;
-
 	cft = __d_cft(file->f_dentry);
-	if (!cft)
-		return -ENODEV;
+
 	if (cft->read_map || cft->read_seq_string) {
 		struct cgroup_seqfile_state *state =
 			kzalloc(sizeof(*state), GFP_USER);
@@ -2461,8 +2457,6 @@ static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
 	struct cgroup *cgrp = dentry->d_fsdata;
 	struct dentry *d;
 	struct cgroup *parent;
-	struct super_block *sb;
-	struct cgroupfs_root *root;
 
 	/* the vfs holds both inode->i_mutex already */
 
@@ -2485,8 +2479,6 @@ static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
 
 	mutex_lock(&cgroup_mutex);
 	parent = cgrp->parent;
-	root = cgrp->root;
-	sb = root->sb;
 
 	if (atomic_read(&cgrp->count)
 	    || !list_empty(&cgrp->children)
@@ -2966,7 +2958,7 @@ int cgroup_clone(struct task_struct *tsk, struct cgroup_subsys *subsys,
 	}
 
 	/* Create the cgroup directory, which also creates the cgroup */
-	ret = vfs_mkdir(inode, dentry, S_IFDIR | 0755);
+	ret = vfs_mkdir(inode, dentry, 0755);
 	child = __d_cgrp(dentry);
 	dput(dentry);
 	if (ret) {
@@ -2976,13 +2968,6 @@ int cgroup_clone(struct task_struct *tsk, struct cgroup_subsys *subsys,
 		goto out_release;
 	}
 
-	if (!child) {
-		printk(KERN_INFO
-		       "Couldn't find new cgroup %s\n", nodename);
-		ret = -ENOMEM;
-		goto out_release;
-	}
-
 	/* The cgroup now exists. Retake cgroup_mutex and check
 	 * that we're still in the same state that we thought we
 	 * were. */
-- 
1.5.4.rc3

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