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Message-ID: <20080622211158.GC31702@martell.zuzino.mipt.ru>
Date: Mon, 23 Jun 2008 01:11:58 +0400
From: Alexey Dobriyan <adobriyan@...il.com>
To: akpm@...l.org
Cc: linux-kernel@...r.kernel.org, viro@...iv.linux.org.uk
Subject: [PATCH] proc: always do ->release
Current two-stage scheme of removing PDE emphasized one bug in proc:
open
rmmod
remove_proc_entry
close
->release won't be called because ->proc_fops were cleared.
In simple cases it's small memory leak.
For every ->open, ->release has to be done. List of openers is introduced
which is traversed at remove_proc_entry() if neeeded.
Discussions with Al long ago (sigh).
Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
---
fs/proc/generic.c | 15 +++++++++
fs/proc/inode.c | 74 +++++++++++++++++++++++++++++++++++++++++++++---
fs/proc/internal.h | 7 ++++
include/linux/proc_fs.h | 1
4 files changed, 93 insertions(+), 4 deletions(-)
--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -597,6 +597,7 @@ static struct proc_dir_entry *__proc_create(struct proc_dir_entry **parent,
ent->pde_users = 0;
spin_lock_init(&ent->pde_unload_lock);
ent->pde_unload_completion = NULL;
+ INIT_LIST_HEAD(&ent->pde_openers);
out:
return ent;
}
@@ -789,6 +790,20 @@ void remove_proc_entry(const char *name, struct proc_dir_entry *parent)
spin_unlock(&de->pde_unload_lock);
continue_removing:
+ spin_lock(&de->pde_unload_lock);
+ while (!list_empty(&de->pde_openers)) {
+ struct pde_opener *pdeo;
+
+ pdeo = list_first_entry(&de->pde_openers, struct pde_opener, lh);
+ list_del(&pdeo->lh);
+ spin_unlock(&de->pde_unload_lock);
+ if (pdeo->release)
+ pdeo->release(pdeo->inode, pdeo->file);
+ kfree(pdeo);
+ spin_lock(&de->pde_unload_lock);
+ }
+ spin_unlock(&de->pde_unload_lock);
+
if (S_ISDIR(de->mode))
parent->nlink--;
de->nlink = 0;
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -119,12 +119,17 @@ static const struct super_operations proc_sops = {
.statfs = simple_statfs,
};
-static void pde_users_dec(struct proc_dir_entry *pde)
+static void __pde_users_dec(struct proc_dir_entry *pde)
{
- spin_lock(&pde->pde_unload_lock);
pde->pde_users--;
if (pde->pde_unload_completion && pde->pde_users == 0)
complete(pde->pde_unload_completion);
+}
+
+static void pde_users_dec(struct proc_dir_entry *pde)
+{
+ spin_lock(&pde->pde_unload_lock);
+ __pde_users_dec(pde);
spin_unlock(&pde->pde_unload_lock);
}
@@ -311,36 +316,97 @@ static int proc_reg_open(struct inode *inode, struct file *file)
struct proc_dir_entry *pde = PDE(inode);
int rv = 0;
int (*open)(struct inode *, struct file *);
+ int (*release)(struct inode *, struct file *);
+ struct pde_opener *pdeo;
+
+ /*
+ * What for, you ask? Well, we can have open, rmmod, remove_proc_entry
+ * sequence. ->release won't be called because ->proc_fops will be
+ * cleared. Depending on complexity of ->release, consequences vary.
+ *
+ * We can't wait for mercy when close will be done for real, it's
+ * deadlockable: rmmod foo </proc/foo . So, we're going to do ->release
+ * by hand in remove_proc_entry(). For this, save opener's credentials
+ * for later.
+ */
+ pdeo = kmalloc(sizeof(struct pde_opener), GFP_KERNEL);
+ if (!pdeo)
+ return -ENOMEM;
spin_lock(&pde->pde_unload_lock);
if (!pde->proc_fops) {
spin_unlock(&pde->pde_unload_lock);
+ kfree(pdeo);
return rv;
}
pde->pde_users++;
open = pde->proc_fops->open;
+ release = pde->proc_fops->release;
spin_unlock(&pde->pde_unload_lock);
if (open)
rv = open(inode, file);
- pde_users_dec(pde);
+ spin_lock(&pde->pde_unload_lock);
+ if (rv == 0) {
+ /* To know what to release. */
+ pdeo->inode = inode;
+ pdeo->file = file;
+ /* Strictly for "too late" ->release in proc_reg_release(). */
+ pdeo->release = release;
+ list_add(&pdeo->lh, &pde->pde_openers);
+ } else
+ kfree(pdeo);
+ __pde_users_dec(pde);
+ spin_unlock(&pde->pde_unload_lock);
return rv;
}
+static struct pde_opener *find_pde_opener(struct proc_dir_entry *pde,
+ struct inode *inode, struct file *file)
+{
+ struct pde_opener *pdeo;
+
+ list_for_each_entry(pdeo, &pde->pde_openers, lh) {
+ if (pdeo->inode == inode && pdeo->file == file)
+ return pdeo;
+ }
+ return NULL;
+}
+
static int proc_reg_release(struct inode *inode, struct file *file)
{
struct proc_dir_entry *pde = PDE(inode);
int rv = 0;
int (*release)(struct inode *, struct file *);
+ struct pde_opener *pdeo;
spin_lock(&pde->pde_unload_lock);
+ pdeo = find_pde_opener(pde, inode, file);
if (!pde->proc_fops) {
- spin_unlock(&pde->pde_unload_lock);
+ /*
+ * Can't simply exit, __fput() will think that everything is OK,
+ * and move on to freeing struct file. remove_proc_entry() will
+ * find slacker in opener's list and will try to do non-trivial
+ * things with struct file. Therefore, remove opener from list.
+ *
+ * But if opener is removed from list, who will ->release it?
+ */
+ if (pdeo) {
+ list_del(&pdeo->lh);
+ spin_unlock(&pde->pde_unload_lock);
+ rv = pdeo->release(inode, file);
+ kfree(pdeo);
+ } else
+ spin_unlock(&pde->pde_unload_lock);
return rv;
}
pde->pde_users++;
release = pde->proc_fops->release;
+ if (pdeo) {
+ list_del(&pdeo->lh);
+ kfree(pdeo);
+ }
spin_unlock(&pde->pde_unload_lock);
if (release)
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -88,3 +88,10 @@ struct dentry *proc_lookup_de(struct proc_dir_entry *de, struct inode *ino,
struct dentry *dentry);
int proc_readdir_de(struct proc_dir_entry *de, struct file *filp, void *dirent,
filldir_t filldir);
+
+struct pde_opener {
+ struct inode *inode;
+ struct file *file;
+ int (*release)(struct inode *, struct file *);
+ struct list_head lh;
+};
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -79,6 +79,7 @@ struct proc_dir_entry {
int pde_users; /* number of callers into module in progress */
spinlock_t pde_unload_lock; /* proc_fops checks and pde_users bumps */
struct completion *pde_unload_completion;
+ struct list_head pde_openers; /* who did ->open, but not ->release */
};
struct kcore_list {
--
1.5.4.5
--
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