* Re: RCU-isms in fs/nfs/delegation.c
2010-04-19 15:33 RCU-isms in fs/nfs/delegation.c David Howells
@ 2010-04-19 17:32 ` Trond Myklebust
2010-04-20 8:48 ` David Howells
0 siblings, 1 reply; 5+ messages in thread
From: Trond Myklebust @ 2010-04-19 17:32 UTC (permalink / raw)
To: David Howells; +Cc: paulmck, linux-nfs, linux-kernel
On Mon, 2010-04-19 at 16:33 +0100, David Howells wrote:
> I'm trying to redo my NFS RCU warning fixup patch on top of Paul's patches,
> and I've found a small potential bug: nfs_inode_reclaim_delegation() doesn't
> use the appropriate accessors/locks to protect NFS_I(inode)->delegation, and
> nor does it use such to protect *delegation that I can see. It just
> overwrites the record.
Hmm... Yes, I think that function should probably take the
rcu_read_lock(), and then take the delegation->lock before modifying the
delegation. Furthermore, it should probably fall back to
nfs_inode_set_delegation() in case we race with a delegreturn. See
below...
> Furthermore, for consistency's sake, it should also protect accesses to
> delegation->cred within that function.
>
> Trond: can you confirm that both NFS_I(inode)->delegation and delegation->cred
> should be considered RCU-protected pointers?
With the above changes to nfs_inode_reclaim_delegation() I don't think
delegation->cred needs to be RCU-protected.
Cheers
Trond
----------------------------------------------------------------------------------------------------------
NFSv4: Fix the locking in nfs_inode_reclaim_delegation()
From: Trond Myklebust <Trond.Myklebust@netapp.com>
Ensure that we correctly rcu-dereference the delegation itself, and that
we protect against removal while we're changing the contents.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
---
fs/nfs/delegation.c | 37 ++++++++++++++++++++++++-------------
1 files changed, 24 insertions(+), 13 deletions(-)
diff --git a/fs/nfs/delegation.c b/fs/nfs/delegation.c
index 1567124..f9c6b63 100644
--- a/fs/nfs/delegation.c
+++ b/fs/nfs/delegation.c
@@ -129,21 +129,32 @@ again:
*/
void nfs_inode_reclaim_delegation(struct inode *inode, struct rpc_cred *cred, struct nfs_openres *res)
{
- struct nfs_delegation *delegation = NFS_I(inode)->delegation;
- struct rpc_cred *oldcred;
+ struct nfs_delegation *delegation;
+ struct rpc_cred *oldcred = NULL;
+ rcu_read_lock();
+ delegation = rcu_dereference(NFS_I(inode)->delegation);
if (delegation == NULL)
- return;
- memcpy(delegation->stateid.data, res->delegation.data,
- sizeof(delegation->stateid.data));
- delegation->type = res->delegation_type;
- delegation->maxsize = res->maxsize;
- oldcred = delegation->cred;
- delegation->cred = get_rpccred(cred);
- clear_bit(NFS_DELEGATION_NEED_RECLAIM, &delegation->flags);
- NFS_I(inode)->delegation_state = delegation->type;
- smp_wmb();
- put_rpccred(oldcred);
+ goto out;
+ spin_lock(&delegation->lock);
+ if (delegation->inode != NULL) {
+ memcpy(delegation->stateid.data, res->delegation.data,
+ sizeof(delegation->stateid.data));
+ delegation->type = res->delegation_type;
+ delegation->maxsize = res->maxsize;
+ oldcred = delegation->cred;
+ delegation->cred = get_rpccred(cred);
+ clear_bit(NFS_DELEGATION_NEED_RECLAIM, &delegation->flags);
+ NFS_I(inode)->delegation_state = delegation->type;
+ spin_unlock(&delegation->lock);
+ put_rpccred(oldcred);
+ } else {
+ /* We appear to have raced with a delegation return. */
+ spin_unlock(&delegation->lock);
+ nfs_inode_set_delegation(inode, cred, res);
+ }
+out:
+ rcu_read_unlock();
}
static int nfs_do_return_delegation(struct inode *inode, struct nfs_delegation *delegation, int issync)
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