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Commit dd14cbc9 authored by Tejun Heo's avatar Tejun Heo Committed by Greg Kroah-Hartman
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sysfs: fix race condition around sd->s_dentry, take#2 



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: default avatarTejun Heo <htejun@gmail.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent 6aa054aa

fs/sysfs/dir.c

+20 −2
Original line number Diff line number Diff line
@@ -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 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;

fs/sysfs/inode.c

+17 −1
Original line number Diff line number Diff line
@@ -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);

	}

}

fs/sysfs/sysfs.h

+1 −0
Original line number Diff line number Diff line
@@ -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;