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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
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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;