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sysfs: fix race condition around sd->s_dentry, take#2

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Allowing attribute and symlink dentries to be reclaimed means
sd->s_dentry can change dynamically.  However, updates to the field
are unsynchronized leading to race conditions.  This patch adds
sysfs_lock and use it to synchronize updates to sd->s_dentry.

Due to the locking around ->d_iput, the check in sysfs_drop_dentry()
is complex.  sysfs_lock only protect sd->s_dentry pointer itself.  The
validity of the dentry is protected by dcache_lock, so whether dentry
is alive or not can only be tested while holding both locks.

This is minimal backport of sysfs_drop_dentry() rewrite in devel
branch.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Tejun Heo 2007-06-11 14:04:01 +09:00 committed by Greg Kroah-Hartman
parent 6aa054aadf
commit dd14cbc994
3 changed files with 38 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

22
fs/sysfs/dir.c
View File

@ -13,14 +13,26 @@
#include "sysfs.h"
DECLARE_RWSEM(sysfs_rename_sem);
spinlock_t sysfs_lock = SPIN_LOCK_UNLOCKED;
static void sysfs_d_iput(struct dentry * dentry, struct inode * inode)
{
struct sysfs_dirent * sd = dentry->d_fsdata;
if (sd) {
BUG_ON(sd->s_dentry != dentry);
sd->s_dentry = NULL;
/* sd->s_dentry is protected with sysfs_lock. This
* allows sysfs_drop_dentry() to dereference it.
*/
spin_lock(&sysfs_lock);
/* The dentry might have been deleted or another
* lookup could have happened updating sd->s_dentry to
* point the new dentry. Ignore if it isn't pointing
* to this dentry.
*/
if (sd->s_dentry == dentry)
sd->s_dentry = NULL;
spin_unlock(&sysfs_lock);
sysfs_put(sd);
}
iput(inode);
@ -247,7 +259,10 @@ static int sysfs_attach_attr(struct sysfs_dirent * sd, struct dentry * dentry)
}
dentry->d_fsdata = sysfs_get(sd);
/* protect sd->s_dentry against sysfs_d_iput */
spin_lock(&sysfs_lock);
sd->s_dentry = dentry;
spin_unlock(&sysfs_lock);
error = sysfs_create(dentry, (attr->mode & S_IALLUGO) | S_IFREG, init);
if (error) {
sysfs_put(sd);
@ -269,7 +284,10 @@ static int sysfs_attach_link(struct sysfs_dirent * sd, struct dentry * dentry)
int err = 0;
dentry->d_fsdata = sysfs_get(sd);
/* protect sd->s_dentry against sysfs_d_iput */
spin_lock(&sysfs_lock);
sd->s_dentry = dentry;
spin_unlock(&sysfs_lock);
err = sysfs_create(dentry, S_IFLNK|S_IRWXUGO, init_symlink);
if (!err) {
dentry->d_op = &sysfs_dentry_ops;

18
fs/sysfs/inode.c
View File

@ -246,9 +246,23 @@ static inline void orphan_all_buffers(struct inode *node)
*/
void sysfs_drop_dentry(struct sysfs_dirent * sd, struct dentry * parent)
{
struct dentry * dentry = sd->s_dentry;
struct dentry *dentry = NULL;
struct inode *inode;
/* We're not holding a reference to ->s_dentry dentry but the
* field will stay valid as long as sysfs_lock is held.
*/
spin_lock(&sysfs_lock);
spin_lock(&dcache_lock);
/* dget dentry if it's still alive */
if (sd->s_dentry && sd->s_dentry->d_inode)
dentry = dget_locked(sd->s_dentry);
spin_unlock(&dcache_lock);
spin_unlock(&sysfs_lock);
/* drop dentry */
if (dentry) {
spin_lock(&dcache_lock);
spin_lock(&dentry->d_lock);
@ -268,6 +282,8 @@ void sysfs_drop_dentry(struct sysfs_dirent * sd, struct dentry * parent)
spin_unlock(&dentry->d_lock);
spin_unlock(&dcache_lock);
}
dput(dentry);
}
}

1
fs/sysfs/sysfs.h
View File

@ -33,6 +33,7 @@ extern const unsigned char * sysfs_get_name(struct sysfs_dirent *sd);
extern void sysfs_drop_dentry(struct sysfs_dirent *sd, struct dentry *parent);
extern int sysfs_setattr(struct dentry *dentry, struct iattr *iattr);
extern spinlock_t sysfs_lock;
extern struct rw_semaphore sysfs_rename_sem;
extern struct super_block * sysfs_sb;
extern const struct file_operations sysfs_dir_operations;