On Apr. 16, 2010, 19:04 +0300, "William A. (Andy) Adamson" <androsadamson@xxxxxxxxx> wrote:
> On Fri, Apr 16, 2010 at 11:52 AM, <andros@xxxxxxxxxx> wrote:
>> From: Andy Adamson <andros@xxxxxxxxxx>
>>
>> A shared RCU device ID cache servicing multiple mounts of a single layout type
>> per meta data server (struct nfs_client).
>>
>> Device IDs of type deviceid4 are required by all layout types, long lived and
>> read at each I/O. They are added to the deviceid cache at first reference by
>> a layout via GETDEVICEINFO and (currently) are only removed at umount.
>>
>> Reference count the device ID cache for each mounted file system
>> in the initialize_mountpoint layoutdriver_io_operation.
>>
>> Dereference the device id cache on file system in the uninitialize_mountpoint
>> layoutdriver_io_operation called at umount
>>
>> Signed-off-by: Andy Adamson <andros@xxxxxxxxxx>
>> ---
>> fs/nfs/pnfs.c | 119 +++++++++++++++++++++++++++++++++++++++++++++
>> include/linux/nfs4_pnfs.h | 27 ++++++++++
>> include/linux/nfs_fs_sb.h | 1 +
>> 3 files changed, 147 insertions(+), 0 deletions(-)
>>
>> diff --git a/fs/nfs/pnfs.c b/fs/nfs/pnfs.c
>> index 91572aa..8492aef 100644
>> --- a/fs/nfs/pnfs.c
>> +++ b/fs/nfs/pnfs.c
>> @@ -45,6 +45,7 @@
>> #include <linux/nfs4.h>
>> #include <linux/pnfs_xdr.h>
>> #include <linux/nfs4_pnfs.h>
>> +#include <linux/rculist.h>
>>
>> #include "internal.h"
>> #include "nfs4_fs.h"
>> @@ -2296,3 +2297,121 @@ struct pnfs_client_operations pnfs_ops = {
>>
>> EXPORT_SYMBOL(pnfs_unregister_layoutdriver);
>> EXPORT_SYMBOL(pnfs_register_layoutdriver);
>> +
>> +
>> +/* Device ID cache. Supports one layout type per struct nfs_client */
>> +int
>> +nfs4_alloc_init_deviceid_cache(struct nfs_client *clp,
>> + void (*free_callback)(struct rcu_head *))
>> +{
>> + struct nfs4_deviceid_cache *c;
>> +
>> + c = kzalloc(sizeof(struct nfs4_deviceid_cache), GFP_KERNEL);
>> + if (!c)
>> + return -ENOMEM;
>> + spin_lock(&clp->cl_lock);
>> + if (clp->cl_devid_cache != NULL) {
>> + kref_get(&clp->cl_devid_cache->dc_kref);
>> + spin_unlock(&clp->cl_lock);
>> + dprintk("%s [kref [%d]]\n", __func__,
>> + atomic_read(&clp->cl_devid_cache->dc_kref.refcount));
>> + kfree(c);
>> + } else {
>> + spin_lock_init(&c->dc_lock);
>> + INIT_LIST_HEAD(&c->dc_deviceids);
>> + kref_init(&c->dc_kref);
>> + c->dc_free_callback = free_callback;
>> + c->dc_clp = clp;
>> + clp->cl_devid_cache = c;
>> + spin_unlock(&clp->cl_lock);
>> + dprintk("%s [new]\n", __func__);
>> + }
>> + return 0;
>> +}
>> +EXPORT_SYMBOL(nfs4_alloc_init_deviceid_cache);
>> +
>> +void
>> +nfs4_init_deviceid_node(struct nfs4_deviceid *d)
>> +{
>> + INIT_LIST_HEAD(&d->de_node);
>> + INIT_RCU_HEAD(&d->de_rcu);
>> +}
>> +EXPORT_SYMBOL(nfs4_init_deviceid_node);
>> +
>> +struct nfs4_deviceid *
>> +nfs4_find_deviceid(struct nfs4_deviceid_cache *c, struct pnfs_deviceid *id)
>> +{
>> + struct nfs4_deviceid *d;
>> +
>> + rcu_read_lock();
>> + list_for_each_entry_rcu(d, &c->dc_deviceids, de_node) {
>> + if (!memcmp(&d->de_id, id, NFS4_PNFS_DEVICEID4_SIZE)) {
>> + rcu_read_unlock();
>> + return d;
>> + }
>> + }
>> + rcu_read_unlock();
I hope this is worth the added complexity...
Out of curiosity, do you have a benchmark comparing the cost
of rcu_read_lock (and unlock) vs. spin_lock(&c->dc_lock)?
>> + return NULL;
>> +}
>> +EXPORT_SYMBOL(nfs4_find_deviceid);
>> +
>> +/*
>> + * Add or kref_get a deviceid.
>> + * GETDEVICEINFOs for same deviceid can race. If deviceid is found, discard new
>> + */
>> +void
>> +nfs4_add_deviceid(struct nfs4_deviceid_cache *c, struct nfs4_deviceid *new)
>> +{
>> + struct nfs4_deviceid *d;
>> +
>> + spin_lock(&c->dc_lock);
>> + list_for_each_entry_rcu(d, &c->dc_deviceids, de_node) {
>> + if (!memcmp(&d->de_id, &new->de_id, NFS4_PNFS_DEVICEID4_SIZE)) {
>> + spin_unlock(&c->dc_lock);
>> + dprintk("%s [discard]\n", __func__);
>> + c->dc_free_callback(&new->de_rcu);
>> + }
>> + }
>> + list_add_rcu(&new->de_node, &c->dc_deviceids);
>> + spin_unlock(&c->dc_lock);
>> + dprintk("%s [new]\n", __func__);
>> +}
>> +EXPORT_SYMBOL(nfs4_add_deviceid);
>> +
>> +static int
>> +nfs4_remove_deviceid(struct nfs4_deviceid_cache *c)
>> +{
>> + struct nfs4_deviceid *d;
>> +
>> + spin_lock(&c->dc_lock);
>> + list_for_each_entry_rcu(d, &c->dc_deviceids, de_node) {
>> + list_del_rcu(&d->de_node);
>> + spin_unlock(&c->dc_lock);
>> + synchronize_rcu();
>> + c->dc_free_callback(&d->de_rcu);
>> + return 1;
>> + }
>> + spin_unlock(&c->dc_lock);
>> + return 0;
>> +}
>> +
>> +static void
>> +nfs4_free_deviceid_cache(struct kref *kref)
>> +{
>> + struct nfs4_deviceid_cache *cache =
>> + container_of(kref, struct nfs4_deviceid_cache, dc_kref);
>> + int more = 1;
>> +
>> + while (more)
>> + more = nfs4_remove_deviceid(cache);
>> + cache->dc_clp->cl_devid_cache = NULL;
>
> Need to take the cl_lock around this assignment
>
> spin_lock(&cache->dc_clp->cl_lock);
> cache->dc_clp->cl_devid_cache = NULL
> spin_unlock(&cache->dc_clp->cl_lock);
>
>
That must happen atomically before kref_put.
It's illegal to have cl_devid_cache be referenced by cache->dc_clp
without a reference count backing it up.
Otherwise, if accessed concurrently to this piece of code
someone might call kref_get while the refcount is zero.
Normally, you'd first clear the referencing pointer to prevent any
new reference to it and only then kref_put it, e.g.:
spin_lock(&cache->dc_clp->cl_lock);
tmp = cache->dc_clp->cl_devid_cache;
cache->dc_clp->cl_devid_cache = NULL
spin_unlock(&cache->dc_clp->cl_lock);
kref_put(&tmp->dc_kref, nfs4_free_deviceid_cache);
Benny
>> + kfree(cache);
>> +}
>> +
>> +void
>> +nfs4_put_deviceid_cache(struct nfs4_deviceid_cache *c)
>> +{
>> + dprintk("%s [%d]\n", __func__, atomic_read(&c->dc_kref.refcount));
>> + kref_put(&c->dc_kref, nfs4_free_deviceid_cache);
>> +}
>> +EXPORT_SYMBOL(nfs4_put_deviceid_cache);
>> diff --git a/include/linux/nfs4_pnfs.h b/include/linux/nfs4_pnfs.h
>> index 1d521f4..2a88a06 100644
>> --- a/include/linux/nfs4_pnfs.h
>> +++ b/include/linux/nfs4_pnfs.h
>> @@ -281,6 +281,33 @@ struct pnfs_devicelist {
>> struct pnfs_deviceid dev_id[NFS4_PNFS_GETDEVLIST_MAXNUM];
>> };
>>
>> +/*
>> + * Device ID RCU cache. A device ID is unique per client ID and layout type.
>> + */
>> +struct nfs4_deviceid_cache {
>> + spinlock_t dc_lock;
>> + struct list_head dc_deviceids;
>> + struct kref dc_kref;
>> + void (*dc_free_callback)(struct rcu_head *);
>> + struct nfs_client *dc_clp;
>> +};
>> +
>> +/* Device ID cache node */
>> +struct nfs4_deviceid {
>> + struct list_head de_node;
>> + struct rcu_head de_rcu;
>> + struct pnfs_deviceid de_id;
>> +};
>> +
>> +extern int nfs4_alloc_init_deviceid_cache(struct nfs_client *,
>> + void (*free_callback)(struct rcu_head *));
>> +extern void nfs4_put_deviceid_cache(struct nfs4_deviceid_cache *);
>> +extern void nfs4_init_deviceid_node(struct nfs4_deviceid *);
>> +extern struct nfs4_deviceid *nfs4_find_deviceid(struct nfs4_deviceid_cache *,
>> + struct pnfs_deviceid *);
>> +extern void nfs4_add_deviceid(struct nfs4_deviceid_cache *,
>> + struct nfs4_deviceid *);
>> +
>> /* pNFS client callback functions.
>> * These operations allow the layout driver to access pNFS client
>> * specific information or call pNFS client->server operations.
>> diff --git a/include/linux/nfs_fs_sb.h b/include/linux/nfs_fs_sb.h
>> index 8522461..ef2e18e 100644
>> --- a/include/linux/nfs_fs_sb.h
>> +++ b/include/linux/nfs_fs_sb.h
>> @@ -87,6 +87,7 @@ struct nfs_client {
>> u32 cl_exchange_flags;
>> struct nfs4_session *cl_session; /* sharred session */
>> struct list_head cl_lo_inodes; /* Inodes having layouts */
>> + struct nfs4_deviceid_cache *cl_devid_cache; /* pNFS deviceid cache */
>> #endif /* CONFIG_NFS_V4_1 */
>>
>> #ifdef CONFIG_NFS_FSCACHE
>> --
>> 1.6.6
>>
>> --
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