Re: [PATCH] NFS: Fix RCU warnings in nfs_inode_return_delegation_noreclaim() [ver #2]

From: David Howells
Date: Wed Apr 07 2010 - 09:23:14 EST

Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> wrote:

> +#define rcu_access_pointer(p, c) \

Why is there a need for 'c'?

> +#define rcu_dereference_protect(p, c) \

I'd prefer rcu_dereference_protected(), I think. This macro doesn't protect
anything. Also, again, why the need for 'c'?

For instance, in:

static struct nfs_delegation *nfs_detach_delegation_locked(struct nfs_inode *nfsi, const nfs4_stateid *stateid)
struct nfs_delegation *delegation =
rcu_dereference_protected(nfsi->delegation, ????);

what would be the condition? That the spinlock is held? That's a condition
for calling the function.

And in:

void nfs_inode_return_delegation_noreclaim(struct inode *inode)
struct nfs_client *clp = NFS_SERVER(inode)->nfs_client;
struct nfs_inode *nfsi = NFS_I(inode);
struct nfs_delegation *delegation;

if (rcu_access_pointer(nfsi->delegation, ????) != NULL) {

what would be the condition here? There's no lock to check - that's the whole
point of the macro. I also can't give it nfsi->delegation to check as the
value may change between the two accesses.

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