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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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