On Wed, Jul 13, 2016 at 04:40:14PM -0400, Chuck Lever wrote:
> nfsd4_release_lockowner finds a lock owner that has no lock state,
> and drops cl_lock. Then release_lockowner picks up cl_lock and
> unhashes the lock owner.
>
> During the window where cl_lock is dropped, I don't see anything
> preventing a concurrent nfsd4_lock from finding that same lock owner
> and adding lock state to it.
>
> Move release_lockowner() into nfsd4_release_lockowner and hang onto
> the cl_lock until after the lock owner's state cannot be found
> again.
>
> Fixes: 2c41beb0e5cf ("nfsd: reduce cl_lock thrashing in ... ")
> Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
Makes sense. Applying with just one line added to the changelog, in
case it's useful to someone: "Found by inspection, we don't currently
have a reproducer."
> ---
> Hi Bruce-
>
> Noticed this recently. I've been running with this patch on my test
> NFS server for over a week. Haven't noticed any issues, but I wonder
> if my clients or tests actually exercise this code in parallel.
>
> The reason I was looking at this area is that one of our internal
> testers encountered a related problem with NFSv4.1. LOCK and
> FREE_STATEID are racing: LOCK returns an existing lock stateid, then
> FREE_STATEID frees that stateid (NFS4_OK). FREE_STATEID should
> return NFS4ERR_LOCKS_HELD in this case?
Looks like free_stateid is deciding whether to return LOCKS_HELD by
inspecting the list of vfs locks, but nfsd4_lock creates the lock
stateid before the vfs lock, so maybe there's a race like:
create lock stateid
free_stateid
vfs_lock_file
but I haven't checked that in detail.
I haven't thought about the protocol side--does hitting this race
require an incorrect client?
--b.
>
> I have not been able to reproduce this, but our tester is able to
> hit it fairly reliably with Oracle's v4.1-based kernel running on
> his server. Recent upstream kernels make the issue rare, but it is
> still encountered on occasion.
>
>
> fs/nfsd/nfs4state.c | 40 +++++++++++++++++-----------------------
> 1 file changed, 17 insertions(+), 23 deletions(-)
>
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index f5f82e1..31c993f 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -1200,27 +1200,6 @@ free_ol_stateid_reaplist(struct list_head *reaplist)
> }
> }
>
> -static void release_lockowner(struct nfs4_lockowner *lo)
> -{
> - struct nfs4_client *clp = lo->lo_owner.so_client;
> - struct nfs4_ol_stateid *stp;
> - struct list_head reaplist;
> -
> - INIT_LIST_HEAD(&reaplist);
> -
> - spin_lock(&clp->cl_lock);
> - unhash_lockowner_locked(lo);
> - while (!list_empty(&lo->lo_owner.so_stateids)) {
> - stp = list_first_entry(&lo->lo_owner.so_stateids,
> - struct nfs4_ol_stateid, st_perstateowner);
> - WARN_ON(!unhash_lock_stateid(stp));
> - put_ol_stateid_locked(stp, &reaplist);
> - }
> - spin_unlock(&clp->cl_lock);
> - free_ol_stateid_reaplist(&reaplist);
> - nfs4_put_stateowner(&lo->lo_owner);
> -}
> -
> static void release_open_stateid_locks(struct nfs4_ol_stateid *open_stp,
> struct list_head *reaplist)
> {
> @@ -5938,6 +5917,7 @@ nfsd4_release_lockowner(struct svc_rqst *rqstp,
> __be32 status;
> struct nfsd_net *nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
> struct nfs4_client *clp;
> + LIST_HEAD (reaplist);
>
> dprintk("nfsd4_release_lockowner clientid: (%08x/%08x):\n",
> clid->cl_boot, clid->cl_id);
> @@ -5968,9 +5948,23 @@ nfsd4_release_lockowner(struct svc_rqst *rqstp,
> nfs4_get_stateowner(sop);
> break;
> }
> + if (!lo) {
> + spin_unlock(&clp->cl_lock);
> + return status;
> + }
> +
> + unhash_lockowner_locked(lo);
> + while (!list_empty(&lo->lo_owner.so_stateids)) {
> + stp = list_first_entry(&lo->lo_owner.so_stateids,
> + struct nfs4_ol_stateid,
> + st_perstateowner);
> + WARN_ON(!unhash_lock_stateid(stp));
> + put_ol_stateid_locked(stp, &reaplist);
> + }
> spin_unlock(&clp->cl_lock);
> - if (lo)
> - release_lockowner(lo);
> + free_ol_stateid_reaplist(&reaplist);
> + nfs4_put_stateowner(&lo->lo_owner);
> +
> return status;
> }
>
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