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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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18
fs/sysfs/inode.c
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@@ -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);
}
}