linux-kernel - Re: [stable] [PATCH] - store sysfs inode nrs in s

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Date:	Mon, 21 May 2007 21:32:40 -0500
From:	Eric Sandeen <sandeen@...deen.net>
To:	Eric Sandeen <sandeen@...hat.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Tejun Heo <htejun@...il.com>,
	Maneesh Soni <maneesh@...ibm.com>, stable@...nel.org
Subject: Re: [stable] [PATCH] - store sysfs inode nrs in s_ino to avoid readdir
 oopses

(2nd try, better(?) changelog, quilt refreshed(!) patch)

--

Backport of
ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.22-rc1/2.6.22-rc1-mm1/broken-out/gregkh-driver-sysfs-allocate-inode-number-using-ida.patch

For regular files in sysfs, sysfs_readdir wants to traverse
sysfs_dirent->s_dentry->d_inode->i_ino to get to the inode number.
But, the dentry can be reclaimed under memory pressure, and there
is no synchronization with readdir.  This patch follows Tejun's
scheme of allocating and storing an inode number in the new s_ino
member of a sysfs_dirent, when dirents are created, and retrieving 
it from there for readdir, so that the pointer chain doesn't have 
to be traversed.

Tejun's upstream patch uses a new-ish "ida" allocator which brings along
some extra complexity; this -stable patch has a brain-dead incrementing
counter which does not guarantee uniqueness, but because sysfs doesn't 
hash inodes as iunique expects, uniqueness wasn't guaranteed today anyway.

Signed-off-by: Eric Sandeen <sandeen@...hat.com>

Index: linux-2.6.21/fs/sysfs/dir.c
===================================================================
--- linux-2.6.21.orig/fs/sysfs/dir.c
+++ linux-2.6.21/fs/sysfs/dir.c
@@ -30,6 +30,14 @@ static struct dentry_operations sysfs_de
 	.d_iput		= sysfs_d_iput,
 };
 
+static unsigned int sysfs_inode_counter;
+ino_t sysfs_get_inum(void)
+{
+	if (unlikely(sysfs_inode_counter < 3))
+		sysfs_inode_counter = 3;
+	return sysfs_inode_counter++;
+}
+
 /*
  * Allocates a new sysfs_dirent and links it to the parent sysfs_dirent
  */
@@ -41,6 +49,7 @@ static struct sysfs_dirent * __sysfs_new
 	if (!sd)
 		return NULL;
 
+	sd->s_ino = sysfs_get_inum();
 	atomic_set(&sd->s_count, 1);
 	atomic_set(&sd->s_event, 1);
 	INIT_LIST_HEAD(&sd->s_children);
@@ -509,7 +518,7 @@ static int sysfs_readdir(struct file * f
 
 	switch (i) {
 		case 0:
-			ino = dentry->d_inode->i_ino;
+			ino = parent_sd->s_ino;
 			if (filldir(dirent, ".", 1, i, ino, DT_DIR) < 0)
 				break;
 			filp->f_pos++;
@@ -538,10 +547,7 @@ static int sysfs_readdir(struct file * f
 
 				name = sysfs_get_name(next);
 				len = strlen(name);
-				if (next->s_dentry)
-					ino = next->s_dentry->d_inode->i_ino;
-				else
-					ino = iunique(sysfs_sb, 2);
+				ino = next->s_ino;
 
 				if (filldir(dirent, name, len, filp->f_pos, ino,
 						 dt_type(next)) < 0)
Index: linux-2.6.21/fs/sysfs/inode.c
===================================================================
--- linux-2.6.21.orig/fs/sysfs/inode.c
+++ linux-2.6.21/fs/sysfs/inode.c
@@ -140,6 +140,7 @@ struct inode * sysfs_new_inode(mode_t mo
 		inode->i_mapping->a_ops = &sysfs_aops;
 		inode->i_mapping->backing_dev_info = &sysfs_backing_dev_info;
 		inode->i_op = &sysfs_inode_operations;
+		inode->i_ino = sd->s_ino;
 		lockdep_set_class(&inode->i_mutex, &sysfs_inode_imutex_key);
 
 		if (sd->s_iattr) {
Index: linux-2.6.21/fs/sysfs/mount.c
===================================================================
--- linux-2.6.21.orig/fs/sysfs/mount.c
+++ linux-2.6.21/fs/sysfs/mount.c
@@ -33,6 +33,7 @@ static struct sysfs_dirent sysfs_root = 
 	.s_element	= NULL,
 	.s_type		= SYSFS_ROOT,
 	.s_iattr	= NULL,
+	.s_ino		= 1,
 };
 
 static void sysfs_clear_inode(struct inode *inode)
Index: linux-2.6.21/fs/sysfs/sysfs.h
===================================================================
--- linux-2.6.21.orig/fs/sysfs/sysfs.h
+++ linux-2.6.21/fs/sysfs/sysfs.h
@@ -5,6 +5,7 @@ struct sysfs_dirent {
 	void 			* s_element;
 	int			s_type;
 	umode_t			s_mode;
+	ino_t			s_ino;
 	struct dentry		* s_dentry;
 	struct iattr		* s_iattr;
 	atomic_t		s_event;

-
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