On Thu, 17 Jul 2014 15:12:29 -0400
Jeff Layton <jlayton@xxxxxxxxxxxxxxx> wrote:
> Move more of the delegation fields to be protected by the fi_lock. It's
> more granular than the state_lock and in later patches we'll want to
> be able to rely on it in addition to the state_lock.
>
> Also, the current code in nfs4_setlease calls vfs_setlease and uses the
> client_mutex to ensure that it doesn't disappear before we can hash the
> delegation. With the client_mutex gone, we'll have a potential race
> condition.
>
> It's possible that the delegation could be recalled after we acquire the
> lease but before we ever get around to hashing it. If that happens, then
> we'd have a nfs4_file that *thinks* it has a delegation, when it
> actually has none.
>
> Attempt to acquire a delegation. If that succeeds, take the spinlocks
> and then check to see if the file has had a conflict show up since then.
> If it has, then we assume that the lease is no longer valid and that
> we shouldn't hand out a delegation.
>
> Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
> ---
> fs/nfsd/nfs4state.c | 54 +++++++++++++++++++++++++++++++++++++++--------------
> 1 file changed, 40 insertions(+), 14 deletions(-)
>
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index fd4deb049ddf..9bc896720db3 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -624,6 +624,8 @@ nfs4_put_delegation(struct nfs4_delegation *dp)
>
> static void nfs4_put_deleg_lease(struct nfs4_file *fp)
> {
> + lockdep_assert_held(&state_lock);
> +
> if (!fp->fi_lease)
> return;
> if (atomic_dec_and_test(&fp->fi_delegees)) {
> @@ -643,11 +645,10 @@ static void
> hash_delegation_locked(struct nfs4_delegation *dp, struct nfs4_file *fp)
> {
> lockdep_assert_held(&state_lock);
> + lockdep_assert_held(&fp->fi_lock);
>
> dp->dl_stid.sc_type = NFS4_DELEG_STID;
> - spin_lock(&fp->fi_lock);
> list_add(&dp->dl_perfile, &fp->fi_delegations);
> - spin_unlock(&fp->fi_lock);
> list_add(&dp->dl_perclnt, &dp->dl_stid.sc_client->cl_delegations);
> }
>
> @@ -659,17 +660,18 @@ unhash_delegation(struct nfs4_delegation *dp)
>
> spin_lock(&state_lock);
> dp->dl_stid.sc_type = NFS4_CLOSED_DELEG_STID;
> + spin_lock(&fp->fi_lock);
> list_del_init(&dp->dl_perclnt);
> list_del_init(&dp->dl_recall_lru);
> - spin_lock(&fp->fi_lock);
> list_del_init(&dp->dl_perfile);
> spin_unlock(&fp->fi_lock);
> - spin_unlock(&state_lock);
> if (fp) {
> nfs4_put_deleg_lease(fp);
> - put_nfs4_file(fp);
> dp->dl_file = NULL;
> }
> + spin_unlock(&state_lock);
> + if (fp)
> + put_nfs4_file(fp);
> }
>
> static void destroy_revoked_delegation(struct nfs4_delegation *dp)
> @@ -3143,8 +3145,8 @@ static void nfsd_break_deleg_cb(struct file_lock *fl)
> */
> fl->fl_break_time = 0;
>
> - fp->fi_had_conflict = true;
> spin_lock(&fp->fi_lock);
> + fp->fi_had_conflict = true;
> list_for_each_entry(dp, &fp->fi_delegations, dl_perfile)
> nfsd_break_one_deleg(dp);
> spin_unlock(&fp->fi_lock);
> @@ -3493,7 +3495,7 @@ static int nfs4_setlease(struct nfs4_delegation *dp)
> {
> struct nfs4_file *fp = dp->dl_file;
> struct file_lock *fl;
> - int status;
> + int status = 0;
>
> fl = nfs4_alloc_init_lease(fp, NFS4_OPEN_DELEGATE_READ);
> if (!fl)
> @@ -3501,15 +3503,31 @@ static int nfs4_setlease(struct nfs4_delegation *dp)
> fl->fl_file = find_readable_file(fp);
> status = vfs_setlease(fl->fl_file, fl->fl_type, &fl);
> if (status)
> - goto out_free;
> + goto out_fput;
> + spin_lock(&state_lock);
> + spin_lock(&fp->fi_lock);
> + /* Did the lease get broken before we took the lock? */
> + status = -EAGAIN;
> + if (fp->fi_had_conflict)
> + goto out_unlock;
So, fwiw -- I think this is a little closer to what HCH was suggesting.
We're not using an atomic flag, per-se but rather a bog standard bool
inside the fi_lock spinlock.
I do have a minor concern that you could have fp->fi_had_conflict flip
to true just before you call vfs_setlease. If that happens you could
end up getting a lease but not hashing the delegation for it.
It seems like an unlikely race though -- if that happens, vfs_setlease
would likely return error, I'd think.
Thoughts?
> + /* Race breaker */
> + if (fp->fi_lease) {
> + status = 0;
> + atomic_inc(&fp->fi_delegees);
> + hash_delegation_locked(dp, fp);
> + goto out_unlock;
> + }
> fp->fi_lease = fl;
> fp->fi_deleg_file = fl->fl_file;
> atomic_set(&fp->fi_delegees, 1);
> - spin_lock(&state_lock);
> hash_delegation_locked(dp, fp);
> + spin_unlock(&fp->fi_lock);
> spin_unlock(&state_lock);
> return 0;
> -out_free:
> +out_unlock:
> + spin_unlock(&fp->fi_lock);
> + spin_unlock(&state_lock);
> +out_fput:
> if (fl->fl_file)
> fput(fl->fl_file);
> locks_free_lock(fl);
> @@ -3518,19 +3536,27 @@ out_free:
>
> static int nfs4_set_delegation(struct nfs4_delegation *dp, struct nfs4_file *fp)
> {
> + int status = 0;
> +
> if (fp->fi_had_conflict)
> return -EAGAIN;
> get_nfs4_file(fp);
> + spin_lock(&state_lock);
> + spin_lock(&fp->fi_lock);
> dp->dl_file = fp;
> - if (!fp->fi_lease)
> + if (!fp->fi_lease) {
> + spin_unlock(&fp->fi_lock);
> + spin_unlock(&state_lock);
> return nfs4_setlease(dp);
> - spin_lock(&state_lock);
> + }
> atomic_inc(&fp->fi_delegees);
> if (fp->fi_had_conflict) {
> - spin_unlock(&state_lock);
> - return -EAGAIN;
> + status = -EAGAIN;
> + goto out_unlock;
> }
> hash_delegation_locked(dp, fp);
> +out_unlock:
> + spin_unlock(&fp->fi_lock);
> spin_unlock(&state_lock);
> return 0;
> }
--
Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
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