Al, do you see any reason this won't work?
After this, all I need to make nfsd happy is a patch to locks.c to
implement delegations, and then a few one-liners to add break_deleg
calls in the right operations. So this is the one non-trivial change I
have to core vfs code.
All of those patches are also ready, and I'd like to merge them for 3.4.
--b.
On Mon, Mar 05, 2012 at 05:38:47PM -0500, bfields wrote:
> From: "J. Bruce Fields" <bfields@xxxxxxxxxx>
>
> A read delegation is used by NFSv4 as a guarantee that a client can
> perform local read opens without informing the server.
>
> The open operation takes the last component of the pathname as an
> argument, thus is also a lookup operation, and giving the client the
> above guarantee means informing the client before we allow anything that
> would change the set of names pointing to the inode.
>
> Therefore, we need to break delegations on rename, link, and unlink.
>
> We also need to prevent new delegations from being acquired while one of
> these operations is in progress.
>
> We could add some completely new locking for that purpose, but it's
> simpler to use the i_mutex, since that's already taken by all the
> operations we care about.
>
> The single exception is rename. So, modify rename to take the i_mutex
> on the file that is being renamed.
>
> Also fix up lockdep and Documentation/filesystems/directory-locking to
> reflect the change.
>
> Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
> ---
> Documentation/filesystems/directory-locking | 11 ++++++-----
> fs/namei.c | 3 +++
> include/linux/fs.h | 9 ++++++---
> 3 files changed, 15 insertions(+), 8 deletions(-)
>
> diff --git a/Documentation/filesystems/directory-locking b/Documentation/filesystems/directory-locking
> index ff7b611..9edbcd2 100644
> --- a/Documentation/filesystems/directory-locking
> +++ b/Documentation/filesystems/directory-locking
> @@ -12,8 +12,8 @@ kinds of locks - per-inode (->i_mutex) and per-filesystem
> locks victim and calls the method.
>
> 4) rename() that is _not_ cross-directory. Locking rules: caller locks
> -the parent, finds source and target, if target already exists - locks it
> -and then calls the method.
> +the parent, finds source and target, locks source, also locks target if
> +it already exists, and then calls the method.
>
> 5) link creation. Locking rules:
> * lock parent
> @@ -30,6 +30,7 @@ rules:
> fail with -ENOTEMPTY
> * if new parent is equal to or is a descendent of source
> fail with -ELOOP
> + * lock source if it is not a directory.
> * if target exists - lock it.
> * call the method.
>
> @@ -56,9 +57,9 @@ objects - A < B iff A is an ancestor of B.
> renames will be blocked on filesystem lock and we don't start changing
> the order until we had acquired all locks).
>
> -(3) any operation holds at most one lock on non-directory object and
> - that lock is acquired after all other locks. (Proof: see descriptions
> - of operations).
> +(3) locks on non-directory objects are acquired only after taking locks
> + on their parents (which remain their parents until all locks are
> + acquired, by (1) and (2)). (Proof: see descriptions of operations).
>
> Now consider the minimal deadlock. Each process is blocked on
> attempt to acquire some lock and already holds at least one lock. Let's
> diff --git a/fs/namei.c b/fs/namei.c
> index 208c6aa..d29b3c4 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -3073,6 +3073,7 @@ static int vfs_rename_other(struct inode *old_dir, struct dentry *old_dentry,
> struct inode *new_dir, struct dentry *new_dentry)
> {
> struct inode *target = new_dentry->d_inode;
> + struct inode *source = old_dentry->d_inode;
> int error;
>
> error = security_inode_rename(old_dir, old_dentry, new_dir, new_dentry);
> @@ -3080,6 +3081,7 @@ static int vfs_rename_other(struct inode *old_dir, struct dentry *old_dentry,
> return error;
>
> dget(new_dentry);
> + mutex_lock_nested(&source->i_mutex, I_MUTEX_RENAME_SOURCE);
> if (target)
> mutex_lock(&target->i_mutex);
>
> @@ -3098,6 +3100,7 @@ static int vfs_rename_other(struct inode *old_dir, struct dentry *old_dentry,
> out:
> if (target)
> mutex_unlock(&target->i_mutex);
> + mutex_unlock(&source->i_mutex);
> dput(new_dentry);
> return error;
> }
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 386da09..e537b67 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -855,10 +855,12 @@ static inline int inode_unhashed(struct inode *inode)
> * 0: the object of the current VFS operation
> * 1: parent
> * 2: child/target
> - * 3: quota file
> + * 3: xattr
> + * 4: quota file
> + * 5: the file being renamed (used only in rename of a non-directory)
> *
> * The locking order between these classes is
> - * parent -> child -> normal -> xattr -> quota
> + * parent -> child -> rename_source -> normal -> xattr -> quota
> */
> enum inode_i_mutex_lock_class
> {
> @@ -866,7 +868,8 @@ enum inode_i_mutex_lock_class
> I_MUTEX_PARENT,
> I_MUTEX_CHILD,
> I_MUTEX_XATTR,
> - I_MUTEX_QUOTA
> + I_MUTEX_QUOTA,
> + I_MUTEX_RENAME_SOURCE
> };
>
> /*
> --
> 1.7.5.4
>
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