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Subject[PATCH] sysfs_remove_dir Vs dcache_readdir race fix
Hi,

sysfs_remove_dir modifies d_subdirs list which results in inconsistency
when there is concurrent dcache_readdir is going on. I think there
is no need for sysfs_remove_dir to modify d_subdirs list and removal
of dentries from d_child list is taken care in the final dput().

The folloing patch fixes this race. The patch is tested by running these two
loops simlutaneously on a SMP box.

#while true; do tree /sys/class/net > /dev/null; done

#while true; do insmod ./dummy.o; rmmod dummy.o; done


o This patch fixes sysfs_remove_dir race with dcache_readdir. There is
no need for sysfs_remove_dir to modify the d_subdirs list for the directory
being deleted as it is taken care in the final dput. Modifying this list
results in inconsistent d_subdirs list and causes infinite loop in
concurrently occuring dcache_readdir.


fs/sysfs/dir.c | 4 +---
1 files changed, 1 insertion(+), 3 deletions(-)

diff -puN fs/sysfs/dir.c~sysfs_remove_dir-race-fix fs/sysfs/dir.c
--- linux-2.6.0-test9-bk24/fs/sysfs/dir.c~sysfs_remove_dir-race-fix 2003-11-20 10:36:13.000000000 +0530
+++ linux-2.6.0-test9-bk24-maneesh/fs/sysfs/dir.c 2003-11-20 10:38:32.000000000 +0530
@@ -122,8 +122,8 @@ void sysfs_remove_dir(struct kobject * k
node = dentry->d_subdirs.next;
while (node != &dentry->d_subdirs) {
struct dentry * d = list_entry(node,struct dentry,d_child);
- list_del_init(node);

+ node = node->next;
pr_debug(" o %s (%d): ",d->d_name.name,atomic_read(&d->d_count));
if (d->d_inode) {
d = dget_locked(d);
@@ -139,9 +139,7 @@ void sysfs_remove_dir(struct kobject * k
spin_lock(&dcache_lock);
}
pr_debug(" done\n");
- node = dentry->d_subdirs.next;
}
- list_del_init(&dentry->d_child);
spin_unlock(&dcache_lock);
up(&dentry->d_inode->i_sem);

_

--
Maneesh Soni
Linux Technology Center,
IBM Software Lab, Bangalore, India
email: maneesh@in.ibm.com
Phone: 91-80-5044999 Fax: 91-80-5268553
T/L : 9243696
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