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    SubjectRe: [PATCH 1/7] sysfs: Serialize updates to the vfs inode
    Quoting Eric W. Biederman (ebiederm@xmission.com):
    > From: Eric W. Biederman <ebiederm@aristanetworks.com>
    >
    > The way the vfs is structured only calls to the filesystem
    > methods actually update the vfs inode. We add to the
    > normal number of places where the vfs inode is updated by
    > also updating the vfs inode in sysfs_refresh_inode.
    >
    > Grabbing the inode mutex in sysfs_permission and sysfs_getattr
    > causes deadlocks, because somtimes those operations are called
    > with the inode mutex held, but not always. Therefore we can
    > not depend upon the inode mutex to serialize all updates
    > to the vfs inode.
    >
    > We take the sysfs_mutex in all of those places so we can
    > also use it to protect the vfs inode. To accomplish that
    > we simply requires extending the vfs inode in sysfs_setattr
    > over inode_change_ok (so we have an unchanging inode
    > when we perform the check), and inode_setattr.
    >
    > Signed-off-by: Eric W. Biederman <ebiederm@aristanetworks.com>

    I'm a little confused about the patch intro: it makes it sound
    like this is preparatory for a followup, but in fact it is a bugfix,
    right? Hard to exploit i think, but should it go to -stable?

    Acked-by: Serge Hallyn <serue@us.ibm.com>

    > ---
    > fs/sysfs/inode.c | 8 ++++----
    > 1 files changed, 4 insertions(+), 4 deletions(-)
    >
    > diff --git a/fs/sysfs/inode.c b/fs/sysfs/inode.c
    > index 220b758..104cbc1 100644
    > --- a/fs/sysfs/inode.c
    > +++ b/fs/sysfs/inode.c
    > @@ -112,20 +112,20 @@ int sysfs_setattr(struct dentry *dentry, struct iattr *iattr)
    > if (!sd)
    > return -EINVAL;
    >
    > + mutex_lock(&sysfs_mutex);
    > error = inode_change_ok(inode, iattr);
    > if (error)
    > - return error;
    > + goto out;
    >
    > iattr->ia_valid &= ~ATTR_SIZE; /* ignore size changes */
    >
    > error = inode_setattr(inode, iattr);
    > if (error)
    > - return error;
    > + goto out;
    >
    > - mutex_lock(&sysfs_mutex);
    > error = sysfs_sd_setattr(sd, iattr);
    > +out:
    > mutex_unlock(&sysfs_mutex);
    > -
    > return error;
    > }
    >
    > --
    > 1.6.5.2.143.g8cc62
    >
    > --
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