On Thu, Aug 20, 2015 at 07:17:06AM -0400, Jeff Layton wrote:
> With the new file caching infrastructure in nfsd, we can end up holding
> files open for an indefinite period of time, even when they are still
> idle. This may prevent the kernel from handing out leases on the file,
> which we don't really want to block.
>
> Fix this by running a blocking notifier call chain whenever on any
> lease attempt. nfsd can then purge the cache for that inode before
> returning.
Could this be expensive? There's potentially a lease attempt on every
NFSv4 open.
Could we use the cache to decide whether a delegation's a good idea?
(So, skip requesting the delegation if the cache gives evidence of
recent activity on the file that would have conflicted with the
delegation we're about to grant.) That might avoid unnecessary cache
purges too.
--b.
>
> Signed-off-by: Jeff Layton <jeff.layton@xxxxxxxxxxxxxxx>
> ---
> fs/locks.c | 15 +++++++++++++++
> fs/nfsd/filecache.c | 27 +++++++++++++++++++++++++++
> include/linux/fs.h | 1 +
> 3 files changed, 43 insertions(+)
>
> diff --git a/fs/locks.c b/fs/locks.c
> index d3d558ba4da7..c81b96159e5c 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -167,6 +167,13 @@ DEFINE_STATIC_LGLOCK(file_lock_lglock);
> static DEFINE_PER_CPU(struct hlist_head, file_lock_list);
>
> /*
> + * Some subsystems would like to be notified if someone attempts to set a
> + * lease on a file. This notifier chain will be called whenever this occurs.
> + */
> +BLOCKING_NOTIFIER_HEAD(lease_notifier_chain);
> +EXPORT_SYMBOL_GPL(lease_notifier_chain);
> +
> +/*
> * The blocked_hash is used to find POSIX lock loops for deadlock detection.
> * It is protected by blocked_lock_lock.
> *
> @@ -1795,10 +1802,18 @@ EXPORT_SYMBOL(generic_setlease);
> *
> * The "priv" pointer is passed directly to the lm_setup function as-is. It
> * may be NULL if the lm_setup operation doesn't require it.
> + *
> + * Kernel subsystems can also register to be notified on any attempt to set
> + * a new lease with the lease_notifier_chain. This is used by (e.g.) nfsd
> + * to close files that it may have cached when there is an attempt to set a
> + * conflicting lease.
> */
> int
> vfs_setlease(struct file *filp, long arg, struct file_lock **lease, void **priv)
> {
> + if (arg != F_UNLCK)
> + blocking_notifier_call_chain(&lease_notifier_chain, arg, *lease);
> +
> if (filp->f_op->setlease)
> return filp->f_op->setlease(filp, arg, lease, priv);
> else
> diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
> index 669e62f6f4f6..77041967d8ff 100644
> --- a/fs/nfsd/filecache.c
> +++ b/fs/nfsd/filecache.c
> @@ -158,6 +158,22 @@ static struct shrinker nfsd_file_shrinker = {
> .seeks = 1,
> };
>
> +static int
> +nfsd_file_lease_notifier_call(struct notifier_block *nb, unsigned long arg,
> + void *data)
> +{
> + struct file_lock *fl = data;
> +
> + /* Don't close files if we're the one trying to set the lease */
> + if (fl->fl_type == FL_LEASE)
> + nfsd_file_close_inode(file_inode(fl->fl_file));
> + return 0;
> +}
> +
> +static struct notifier_block nfsd_file_lease_notifier = {
> + .notifier_call = nfsd_file_lease_notifier_call,
> +};
> +
> int
> nfsd_file_cache_init(void)
> {
> @@ -186,12 +202,21 @@ nfsd_file_cache_init(void)
> goto out_lru;
> }
>
> + ret = blocking_notifier_chain_register(&lease_notifier_chain,
> + &nfsd_file_lease_notifier);
> + if (ret) {
> + pr_err("nfsd: unable to register lease notifier: %d\n", ret);
> + goto out_shrinker;
> + }
> +
> for (i = 0; i < NFSD_FILE_HASH_SIZE; i++) {
> INIT_HLIST_HEAD(&nfsd_file_hashtbl[i].nfb_head);
> spin_lock_init(&nfsd_file_hashtbl[i].nfb_lock);
> }
> out:
> return ret;
> +out_shrinker:
> + unregister_shrinker(&nfsd_file_shrinker);
> out_lru:
> list_lru_destroy(&nfsd_file_lru);
> out_err:
> @@ -207,6 +232,8 @@ nfsd_file_cache_shutdown(void)
> struct nfsd_file *nf;
> LIST_HEAD(dispose);
>
> + blocking_notifier_chain_unregister(&lease_notifier_chain,
> + &nfsd_file_lease_notifier);
> unregister_shrinker(&nfsd_file_shrinker);
> for (i = 0; i < NFSD_FILE_HASH_SIZE; i++) {
> spin_lock(&nfsd_file_hashtbl[i].nfb_lock);
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 9a9d314f7b27..01bb82eae684 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1041,6 +1041,7 @@ extern int fcntl_setlease(unsigned int fd, struct file *filp, long arg);
> extern int fcntl_getlease(struct file *filp);
>
> /* fs/locks.c */
> +extern struct blocking_notifier_head lease_notifier_chain;
> void locks_free_lock_context(struct file_lock_context *ctx);
> void locks_free_lock(struct file_lock *fl);
> extern void locks_init_lock(struct file_lock *);
> --
> 2.4.3
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