On 10/25, Chuck Lever wrote:
>
> > Another question is why we can't simply turn nn->writeverf into seqcount_t.
> > I guess we can't because nfsd_reset_write_verifier() needs spin_lock() to
> > serialise with itself, right?
>
> "reset" is supposed to be very rare operation. Using a lock in that
> case is probably quite acceptable, as long as reading the verifier
> is wait-free and guaranteed to be untorn.
>
> But a seqcount_t is only 32 bits.
Again, I don't understand you.
Once again, we can turn writeverf into seqcount_t, see the patch below.
But this way nfsd_reset_write_verifier() can race with itself, no?
Oleg
---
diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
index ec49b200b797..3e2adf3eb15f 100644
--- a/fs/nfsd/netns.h
+++ b/fs/nfsd/netns.h
@@ -110,7 +110,7 @@ struct nfsd_net {
bool nfsd_net_up;
bool lockd_up;
- seqlock_t writeverf_lock;
+ seqcount_t writeverf_lock;
unsigned char writeverf[8];
/*
diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index 7ed02fb88a36..6320491018f8 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -1523,7 +1523,7 @@ static __net_init int nfsd_net_init(struct net *net)
nn->nfsd4_minorversions = NULL;
nfsd4_init_leases_net(nn);
get_random_bytes(&nn->siphash_key, sizeof(nn->siphash_key));
- seqlock_init(&nn->writeverf_lock);
+ seqcount_init(&nn->writeverf_lock);
return 0;
diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
index c7af1095f6b5..fc4e31411508 100644
--- a/fs/nfsd/nfssvc.c
+++ b/fs/nfsd/nfssvc.c
@@ -359,13 +359,12 @@ static bool nfsd_needs_lockd(struct nfsd_net *nn)
*/
void nfsd_copy_write_verifier(__be32 verf[2], struct nfsd_net *nn)
{
- int seq = 0;
+ int seq;
do {
- read_seqbegin_or_lock(&nn->writeverf_lock, &seq);
+ seq = read_seqcount_begin(&nn->writeverf_lock);
memcpy(verf, nn->writeverf, sizeof(nn->writeverf));
- } while (need_seqretry(&nn->writeverf_lock, seq));
- done_seqretry(&nn->writeverf_lock, seq);
+ } while (read_seqcount_retry(&nn->writeverf_lock, seq));
}
static void nfsd_reset_write_verifier_locked(struct nfsd_net *nn)
@@ -397,9 +396,9 @@ static void nfsd_reset_write_verifier_locked(struct nfsd_net *nn)
*/
void nfsd_reset_write_verifier(struct nfsd_net *nn)
{
- write_seqlock(&nn->writeverf_lock);
+ write_seqcount_begin(&nn->writeverf_lock);
nfsd_reset_write_verifier_locked(nn);
- write_sequnlock(&nn->writeverf_lock);
+ write_seqcount_end(&nn->writeverf_lock);
}
/*
