Messages in this thread | | | Date | Fri, 26 Jul 2013 17:59:00 +0800 | From | Dennis Chen <> | Subject | Re: [PATCH] race condition fixing in sysfs_create_dir |
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On 07/26/2013 05:49 PM, Dennis Chen wrote:
> The patch is trying its best to avoid creating a dir under a parent dir which is removing from > the system: > PATH0 (create a dir under 'PARENT/...') PATH1 (remove the 'PARENT/...') > sysfs_create_dir() { sysfs_remove_dir() { > ... ... > if (kobj->parent) spin_lock(&sysfs_assoc_lock); > parent_sd = kobj->parent->sd; <----- kobj->sd = NULL; > else spin_unlock(&sysfs_assoc_lock); > parent_sd = &sysfs_root; > Suppose PATH1 enter the critical section first, then PATH0 begin to execute before kobj->sd > has been reset to NULL, possibly PATH0 will get a non-NULL parent_sd since lack of the > sysfs_assoc_lock protection in PATH0. In this case, PATH0 think it has a valid parent_sd which > can be freed by PATH1 in the followed, refer to the comments in the patch. Maybe we need > to figure out a perfect solution to solve the race condition, although the codes in question are > in slow path... > Signed-off-by: Dennis Chen <xschen@tnsoft.com.cn> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > Cc: Tejun Heo <teheo@suse.de>
should be Tejun Heo <tj@kernel.org>
> Cc: Wang Cong <xiyou.wangcong@gmail.com> > --- > fs/sysfs/dir.c | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) > diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c > index e068e74..114073d 100644 > --- a/fs/sysfs/dir.c > +++ b/fs/sysfs/dir.c > @@ -746,13 +746,22 @@ int sysfs_create_dir(struct kobject * kobj) > BUG_ON(!kobj); > + spin_lock(&sysfs_assoc_lock); > if (kobj->parent) > parent_sd = kobj->parent->sd; > else > parent_sd = &sysfs_root; > - if (!parent_sd) > + if (!parent_sd) { > + spin_unlock(&sysfs_assoc_lock); > return -ENOENT; > + } > + spin_unlock(&sysfs_assoc_lock); > + /* TODO: although the sysfs is in a slow path, but in the operation > + * followed, we still have a window to let the sysfs_remove_dir to > + * free the memory space pointered by parent_sd till we inc its ref > + * count in __sysfs_add_one() > + */ > if (sysfs_ns_type(parent_sd)) > ns = kobj->ktype->namespace(kobj);
Re CC Tejun whose email addess <@suse.de> is obsolete :)
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