Attachment 309776 Details for Bug 448603 – patch -- fix off-by-one in module_ref counts

[patch] patch -- fix off-by-one in module_ref counts

0001-BZ-448603-kmod-try-to-make-it-so-that-holding-a-pr.patch (text/plain), 3.18 KB, created by Jeff Layton on 2008-06-18 18:46:23 UTC

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Creator: Jeff Layton

Created: 2008-06-18 18:46:23 UTC

Size: 3.18 KB

patch

obsolete

>From bb98c352da5f1fdfce63c0e3a3906055a1be3bdf Mon Sep 17 00:00:00 2001
>From: Jeff Layton <jlayton@redhat.com>
>Date: Wed, 18 Jun 2008 14:27:40 -0400
>Subject: [PATCH] BZ#448603: kmod: try to make it so that holding a procfile open keeps a module reference
>
>The patch for bug 280431 moved the module refcounting from the
>lookup/close codepath to the read/write codepath. This doesn't work
>quite right when a program holds open a procfile and polls it
>periodically. In particular, some nfs daemons do this.
>
>This patch attempts to put the module refcounting back into the
>lookup/close codepath, but attempts to do it in a way that won't make
>the refcount go negative. It's fairly impossible to do this perfectly in
>a way that's kABI safe. It's still possible with this patch to do a
>lookup/open and not get a reference, but it should keep us from doing
>more module_put's than gets.
>---
> fs/proc/inode.c         |   18 +++++++++++++++---
> include/linux/proc_fs.h |    1 +
> 2 files changed, 16 insertions(+), 3 deletions(-)
>
>diff --git a/fs/proc/inode.c b/fs/proc/inode.c
>index 3b15180..7aa2e71 100644
>--- a/fs/proc/inode.c
>+++ b/fs/proc/inode.c
>@@ -60,15 +60,18 @@ static void proc_delete_inode(struct inode *inode)
> {
> 	struct proc_dir_entry *de;
> 	struct task_struct *tsk;
>+	struct proc_inode *ei = PROC_I(inode);
> 
> 	/* Let go of any associated process */
>-	tsk = PROC_I(inode)->task;
>+	tsk = ei->task;
> 	if (tsk)
> 		put_task_struct(tsk);
> 
> 	/* Let go of any associated proc directory entry */
>-	de = PROC_I(inode)->pde;
>+	de = ei->pde;
> 	if (de) {
>+		if (de->owner && !atomic_add_negative(-1, &ei->module_refs))
>+			module_put(de->owner);
> 		de_put(de);
> 	}
> 	clear_inode(inode);
>@@ -95,6 +98,7 @@ static struct inode *proc_alloc_inode(struct super_block *sb)
> 	ei->type = 0;
> 	ei->op.proc_get_link = NULL;
> 	ei->pde = NULL;
>+	atomic_set(&ei->module_refs, 0);
> 	inode = &ei->vfs_inode;
> 	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
> 	return inode;
>@@ -190,6 +194,7 @@ struct inode *proc_get_inode(struct super_block *sb, unsigned int ino,
> 				struct proc_dir_entry *de)
> {
> 	struct inode * inode;
>+	struct proc_inode *ei;
> 
> 	/*
> 	 * Increment the use count so the dir entry can't disappear.
>@@ -202,7 +207,8 @@ struct inode *proc_get_inode(struct super_block *sb, unsigned int ino,
> 	if (!inode)
> 		goto out_fail;
> 	
>-	PROC_I(inode)->pde = de;
>+	ei = PROC_I(inode);
>+	ei->pde = de;
> 	if (de) {
> 		if (de->mode) {
> 			inode->i_mode = de->mode;
>@@ -213,6 +219,12 @@ struct inode *proc_get_inode(struct super_block *sb, unsigned int ino,
> 			inode->i_size = de->size;
> 		if (de->nlink)
> 			inode->i_nlink = de->nlink;
>+		/* get a module reference if module is non-NULL */
>+		if (de->owner) {
>+			if (!try_module_get(de->owner))
>+				goto out_fail;
>+			atomic_inc(&ei->module_refs);
>+		}
> 		if (de->proc_iops)
> 			inode->i_op = de->proc_iops;
> 		if (de->proc_fops)
>diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
>index 4dec024..4fbf2bf 100644
>--- a/include/linux/proc_fs.h
>+++ b/include/linux/proc_fs.h
>@@ -281,6 +281,7 @@ struct proc_inode {
> 	} op;
> 	struct proc_dir_entry *pde;
> 	struct inode vfs_inode;
>+	atomic_t	module_refs;
> };
> 
> static inline struct proc_inode *PROC_I(const struct inode *inode)
>-- 
>1.5.5.1
>

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