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SubjectRe: [PATCHSET] idr: implement idr_alloc() and convert existing users
On Sun, Feb 03, 2013 at 12:02:41PM -0500, J. Bruce Fields wrote:
> On Sat, Feb 02, 2013 at 05:20:01PM -0800, Tejun Heo wrote:
> > * Bruce, I couldn't convert nfsd. Can you please help? More on it
> > later.
> ...
> > I converted all in-kernel users except nfsd and staging drivers. nfsd
> > splits preloading and actual id allocation in a way that per-cpu
> > preloading can't be used. I couldn't follow the control flow to
> > verify whether the current code is correct either. I think the best
> > way would be allocating ID upfront without installing the handle and
> > then later using idr_replace() to install the pointer when the ID
> > actually gets used. Bruce, would something like that be possible?
>
> Actually, I'm not even sure if that's necessary, we can probably just
> do it all at the start.
>
> I'll try to have a patch doing that tomorrow.

So, something like this.

--b.

commit 9847160469b40345e1d78a7cbf9536761bb47d91
Author: J. Bruce Fields <bfields@redhat.com>
Date: Sun Feb 3 12:23:01 2013 -0500

nfsd4: simplify idr allocation

We don't really need to preallocate at all; just allocate and initialize
everything at once, but leave the sc_type field initially 0 to prevent
finding the stateid till it's fully initialized.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 4db46aa..485b1f7 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -261,33 +261,46 @@ static inline int get_new_stid(struct nfs4_stid *stid)
return new_stid;
}

-static void init_stid(struct nfs4_stid *stid, struct nfs4_client *cl, unsigned char type)
+static struct nfs4_stid *nfs4_alloc_stid(struct nfs4_client *cl, struct
+kmem_cache *slab)
{
- stateid_t *s = &stid->sc_stateid;
+ struct idr *stateids = &cl->cl_stateids;
+ static int min_stateid = 0;
+ struct nfs4_stid *stid;
int new_id;

- stid->sc_type = type;
+ stid = kmem_cache_alloc(slab, GFP_KERNEL);
+ if (!stid)
+ return NULL;
+
+ if (!idr_pre_get(stateids, GFP_KERNEL))
+ goto out_free;
+ if (idr_get_new_above(stateids, stid, min_stateid, &new_id))
+ goto out_free;
stid->sc_client = cl;
- s->si_opaque.so_clid = cl->cl_clientid;
- new_id = get_new_stid(stid);
- s->si_opaque.so_id = (u32)new_id;
+ stid->sc_type = 0;
+ stid->sc_stateid.si_opaque.so_id = new_id;
+ stid->sc_stateid.si_opaque.so_clid = cl->cl_clientid;
/* Will be incremented before return to client: */
- s->si_generation = 0;
-}
+ stid->sc_stateid.si_generation = 0;

-static struct nfs4_stid *nfs4_alloc_stid(struct nfs4_client *cl, struct kmem_cache *slab)
-{
- struct idr *stateids = &cl->cl_stateids;
-
- if (!idr_pre_get(stateids, GFP_KERNEL))
- return NULL;
/*
- * Note: if we fail here (or any time between now and the time
- * we actually get the new idr), we won't need to undo the idr
- * preallocation, since the idr code caps the number of
- * preallocated entries.
+ * It shouldn't be a problem to reuse an opaque stateid value.
+ * I don't think it is for 4.1. But with 4.0 I worry that, for
+ * example, a stray write retransmission could be accepted by
+ * the server when it should have been rejected. Therefore,
+ * adopt a trick from the sctp code to attempt to maximize the
+ * amount of time until an id is reused, by ensuring they always
+ * "increase" (mod INT_MAX):
*/
- return kmem_cache_alloc(slab, GFP_KERNEL);
+
+ min_stateid = new_id+1;
+ if (min_stateid == INT_MAX)
+ min_stateid = 0;
+ return stid;
+out_free:
+ kfree(stid);
+ return NULL;
}

static struct nfs4_ol_stateid * nfs4_alloc_stateid(struct nfs4_client *clp)
@@ -316,7 +329,7 @@ alloc_init_deleg(struct nfs4_client *clp, struct nfs4_ol_stateid *stp, struct sv
dp = delegstateid(nfs4_alloc_stid(clp, deleg_slab));
if (dp == NULL)
return dp;
- init_stid(&dp->dl_stid, clp, NFS4_DELEG_STID);
+ dp->dl_stid.sc_type = NFS4_DELEG_STID;
/*
* delegation seqid's are never incremented. The 4.1 special
* meaning of seqid 0 isn't meaningful, really, but let's avoid
@@ -337,13 +350,21 @@ alloc_init_deleg(struct nfs4_client *clp, struct nfs4_ol_stateid *stp, struct sv
return dp;
}

+void free_stid(struct nfs4_stid *s, struct kmem_cache *slab)
+{
+ struct idr *stateids = &s->sc_client->cl_stateids;
+
+ idr_remove(stateids, s->sc_stateid.si_opaque.so_id);
+ kmem_cache_free(slab, s);
+}
+
void
nfs4_put_delegation(struct nfs4_delegation *dp)
{
if (atomic_dec_and_test(&dp->dl_count)) {
dprintk("NFSD: freeing dp %p\n",dp);
put_nfs4_file(dp->dl_file);
- kmem_cache_free(deleg_slab, dp);
+ free_stid(&dp->dl_stid, deleg_slab);
num_delegations--;
}
}
@@ -360,9 +381,7 @@ static void nfs4_put_deleg_lease(struct nfs4_file *fp)

static void unhash_stid(struct nfs4_stid *s)
{
- struct idr *stateids = &s->sc_client->cl_stateids;
-
- idr_remove(stateids, s->sc_stateid.si_opaque.so_id);
+ s->sc_type = 0;
}

/* Called under the state lock. */
@@ -519,7 +538,7 @@ static void close_generic_stateid(struct nfs4_ol_stateid *stp)

static void free_generic_stateid(struct nfs4_ol_stateid *stp)
{
- kmem_cache_free(stateid_slab, stp);
+ free_stid(&stp->st_stid, stateid_slab);
}

static void release_lock_stateid(struct nfs4_ol_stateid *stp)
@@ -1258,7 +1277,12 @@ static void gen_confirm(struct nfs4_client *clp)

static struct nfs4_stid *find_stateid(struct nfs4_client *cl, stateid_t *t)
{
- return idr_find(&cl->cl_stateids, t->si_opaque.so_id);
+ struct nfs4_stid *ret;
+
+ ret = idr_find(&cl->cl_stateids, t->si_opaque.so_id);
+ if (!ret || !ret->sc_type)
+ return NULL;
+ return ret;
}

static struct nfs4_stid *find_stateid_by_type(struct nfs4_client *cl, stateid_t *t, char typemask)
@@ -2444,9 +2468,8 @@ alloc_init_open_stateowner(unsigned int strhashval, struct nfs4_client *clp, str

static void init_open_stateid(struct nfs4_ol_stateid *stp, struct nfs4_file *fp, struct nfsd4_open *open) {
struct nfs4_openowner *oo = open->op_openowner;
- struct nfs4_client *clp = oo->oo_owner.so_client;

- init_stid(&stp->st_stid, clp, NFS4_OPEN_STID);
+ stp->st_stid.sc_type = NFS4_OPEN_STID;
INIT_LIST_HEAD(&stp->st_lockowners);
list_add(&stp->st_perstateowner, &oo->oo_owner.so_stateids);
list_add(&stp->st_perfile, &fp->fi_stateids);
@@ -4032,7 +4055,7 @@ alloc_init_lock_stateid(struct nfs4_lockowner *lo, struct nfs4_file *fp, struct
stp = nfs4_alloc_stateid(clp);
if (stp == NULL)
return NULL;
- init_stid(&stp->st_stid, clp, NFS4_LOCK_STID);
+ stp->st_stid.sc_type = NFS4_LOCK_STID;
list_add(&stp->st_perfile, &fp->fi_stateids);
list_add(&stp->st_perstateowner, &lo->lo_owner.so_stateids);
stp->st_stateowner = &lo->lo_owner;

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