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kernfs: protect lazy kernfs_iattrs allocation with mutex

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kernfs_iattrs is allocated lazily when operations which require it
take place; unfortunately, the lazy allocation and returning weren't
properly synchronized and when there are multiple concurrent
operations, it might end up returning kernfs_iattrs which hasn't
finished initialization yet or different copies to different callers.

Fix it by synchronizing with a mutex.  This can be smarter with memory
barriers but let's go there if it actually turns out to be necessary.

Signed-off-by: Tejun Heo <tj@kernel.org>
Link: http://lkml.kernel.org/g/533ABA32.9080602@oracle.com
Reported-by: Sasha Levin <sasha.levin@oracle.com>
Cc: stable@vger.kernel.org # 3.14
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Tejun Heo
2014-04-02 16:40:52 -04:00
committed by Greg Kroah-Hartman
parent a2a4dc494a
commit 4afddd60a7
1 changed files with 10 additions and 4 deletions
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14
fs/kernfs/inode.c
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@ -48,14 +48,18 @@ void __init kernfs_inode_init(void)
static struct kernfs_iattrs *kernfs_iattrs(struct kernfs_node *kn) static struct kernfs_iattrs *kernfs_iattrs(struct kernfs_node *kn)
{ {
static DEFINE_MUTEX(iattr_mutex);
struct kernfs_iattrs *ret;
struct iattr *iattrs; struct iattr *iattrs;
mutex_lock(&iattr_mutex);
if (kn->iattr) if (kn->iattr)
return kn->iattr; goto out_unlock;
kn->iattr = kzalloc(sizeof(struct kernfs_iattrs), GFP_KERNEL); kn->iattr = kzalloc(sizeof(struct kernfs_iattrs), GFP_KERNEL);
if (!kn->iattr) if (!kn->iattr)
return NULL; goto out_unlock;
iattrs = &kn->iattr->ia_iattr; iattrs = &kn->iattr->ia_iattr;
/* assign default attributes */ /* assign default attributes */
@ -65,8 +69,10 @@ static struct kernfs_iattrs *kernfs_iattrs(struct kernfs_node *kn)
iattrs->ia_atime = iattrs->ia_mtime = iattrs->ia_ctime = CURRENT_TIME; iattrs->ia_atime = iattrs->ia_mtime = iattrs->ia_ctime = CURRENT_TIME;
simple_xattrs_init(&kn->iattr->xattrs); simple_xattrs_init(&kn->iattr->xattrs);
out_unlock:
return kn->iattr; ret = kn->iattr;
mutex_unlock(&iattr_mutex);
return ret;
} }
static int __kernfs_setattr(struct kernfs_node *kn, const struct iattr *iattr) static int __kernfs_setattr(struct kernfs_node *kn, const struct iattr *iattr)