From: Glauber Costa Subject: Re: [PATCH 02/12] container quota: lock/unlock mount namespace when performing quotactl. Date: Thu, 31 May 2012 13:04:24 +0400 Message-ID: <4FC73418.1040402@parallels.com> References: <1338389946-13711-1-git-send-email-jeff.liu@oracle.com> <1338389946-13711-3-git-send-email-jeff.liu@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Cc: jack-AlSwsSmVLrQ@public.gmane.org, tytso-3s7WtUTddSA@public.gmane.org, containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, david-FqsqvQoI3Ljby3iVrkZq2A@public.gmane.org, hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org, bpm-sJ/iWh9BUns@public.gmane.org, christopher.jones-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org, linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, tm-d1IQDZat3X0@public.gmane.org, linux-ext4-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, chris.mason-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org, tinguely-sJ/iWh9BUns@public.gmane.org To: Return-path: In-Reply-To: <1338389946-13711-3-git-send-email-jeff.liu-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org List-Id: linux-ext4.vger.kernel.org On 05/30/2012 06:58 PM, jeff.liu-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org wrote: > Introduce two functions to lock/unlock a particular mount namespace > when container quota operations is performed. > > Signed-off-by: Jie Liu > --- > fs/namespace.c | 17 +++++++++++++++++ > include/linux/mnt_namespace.h | 13 +++++++++++++ > 2 files changed, 30 insertions(+), 0 deletions(-) > > diff --git a/fs/namespace.c b/fs/namespace.c > index e608199..8823ba8 100644 > --- a/fs/namespace.c > +++ b/fs/namespace.c > @@ -2633,3 +2633,20 @@ bool our_mnt(struct vfsmount *mnt) > { > return check_mnt(real_mount(mnt)); > } > + > +/* > + * Lock the mount namespace when performing a particular container > + * disk quotactl operation, especially to protect removing it. > + */ > +void lock_mnt_ns(struct mnt_namespace *ns) > +{ > + down_write(&namespace_sem); > +} > + > +/* > + * Unlock the mount namespace after quotactl on that was done. > + */ > +void unlock_mnt_ns(struct mnt_namespace *ns) > +{ > + up_write(&namespace_sem); > +} > diff --git a/include/linux/mnt_namespace.h b/include/linux/mnt_namespace.h > index 5a8e390..ff72ed5 100644 > --- a/include/linux/mnt_namespace.h > +++ b/include/linux/mnt_namespace.h > @@ -9,6 +9,19 @@ extern struct mnt_namespace *copy_mnt_ns(unsigned long, struct mnt_namespace *, > struct fs_struct *); > extern void put_mnt_ns(struct mnt_namespace *ns); > > +#ifdef CONFIG_NS_QUOTA > +extern void lock_mnt_ns(struct mnt_namespace *); > +extern void unlock_mnt_ns(struct mnt_namespace *); > +#else > +void lock_mnt_ns(struct mnt_namespace *) > +{ > +} > + > +void unlock_mnt_ns(struct mnt_namespace *) > +{ > +} > +#endif > + Seems weird. There is nothing ns-quota specific in locking a namespace. Also, just grabbing a lock from an outer subsystem is quite ugly. If you are grabbing a namespace lock, this suggests you are tweaking namespace data. So you should have that file provide you with a function that does the full operation. Of course there are exceptions to that, but it rings a bell.