Commit 1023e90b authored by Paulo Alcantara's avatar Paulo Alcantara Committed by Steve French
Browse files

cifs: avoid starvation when refreshing dfs cache 



When refreshing the DFS cache, keep SMB2 IOCTL calls as much outside
critical sections as possible and avoid read/write starvation when
getting new DFS referrals by using broken or slow connections.

Signed-off-by: default avatarPaulo Alcantara (SUSE) <pc@cjr.nz>
Reviewed-by: default avatarAurelien Aptel <aaptel@suse.com>
Signed-off-by: default avatarSteve French <stfrench@microsoft.com>
parent 0d52df81

fs/cifs/dfs_cache.c

+105 −40
Original line number Diff line number Diff line
@@ -554,6 +554,8 @@ static void remove_oldest_entry_locked(void) 
	struct cache_entry *ce;

	struct cache_entry *to_del = NULL;



	WARN_ON(!rwsem_is_locked(&htable_rw_lock));



	for (i = 0; i < CACHE_HTABLE_SIZE; i++) {

		struct hlist_head *l = &cache_htable[i];
@@ -583,7 +585,13 @@ static int add_cache_entry_locked(struct dfs_info3_param *refs, int numrefs) 
	struct cache_entry *ce;

	unsigned int hash;



	convert_delimiter(refs[0].path_name, '\\');

	WARN_ON(!rwsem_is_locked(&htable_rw_lock));



	if (atomic_read(&cache_count) >= CACHE_MAX_ENTRIES) {

		cifs_dbg(FYI, "%s: reached max cache size (%d)\n", __func__, CACHE_MAX_ENTRIES);

		remove_oldest_entry_locked();

	}



	rc = cache_entry_hash(refs[0].path_name, strlen(refs[0].path_name), &hash);

	if (rc)

		return rc;
@@ -605,6 +613,8 @@ static int add_cache_entry_locked(struct dfs_info3_param *refs, int numrefs) 
	hlist_add_head(&ce->hlist, &cache_htable[hash]);

	dump_ce(ce);



	atomic_inc(&cache_count);



	return 0;

}
@@ -719,16 +729,13 @@ void dfs_cache_destroy(void) 
}



/* Update a cache entry with the new referral in @refs */

static int update_cache_entry_locked(const char *path, const struct dfs_info3_param *refs,

static int update_cache_entry_locked(struct cache_entry *ce, const struct dfs_info3_param *refs,

				     int numrefs)

{

	int rc;

	struct cache_entry *ce;

	char *s, *th = NULL;



	ce = lookup_cache_entry(path);

	if (IS_ERR(ce))

		return PTR_ERR(ce);

	WARN_ON(!rwsem_is_locked(&htable_rw_lock));



	if (ce->tgthint) {

		s = ce->tgthint->name;
@@ -750,18 +757,28 @@ static int update_cache_entry_locked(const char *path, const struct dfs_info3_pa 
static int get_dfs_referral(const unsigned int xid, struct cifs_ses *ses, const char *path,

			    struct dfs_info3_param **refs, int *numrefs)

{

	int rc;

	int i;



	cifs_dbg(FYI, "%s: get an DFS referral for %s\n", __func__, path);



	*refs = NULL;

	*numrefs = 0;



	if (!ses || !ses->server || !ses->server->ops->get_dfs_refer)

		return -EOPNOTSUPP;

	if (unlikely(!cache_cp))

		return -EINVAL;



	*refs = NULL;

	*numrefs = 0;



	return ses->server->ops->get_dfs_refer(xid, ses, path, refs, numrefs, cache_cp,

	rc =  ses->server->ops->get_dfs_refer(xid, ses, path, refs, numrefs, cache_cp,

					      NO_MAP_UNI_RSVD);

	if (!rc) {

		struct dfs_info3_param *ref = *refs;



		for (i = 0; i < *numrefs; i++)

			convert_delimiter(ref[i].path_name, '\\');

	}

	return rc;

}



/*
@@ -807,18 +824,11 @@ static int cache_refresh_path(const unsigned int xid, struct cifs_ses *ses, cons 
	dump_refs(refs, numrefs);



	if (!newent) {

		rc = update_cache_entry_locked(path, refs, numrefs);

		rc = update_cache_entry_locked(ce, refs, numrefs);

		goto out_unlock;

	}



	if (atomic_read(&cache_count) >= CACHE_MAX_ENTRIES) {

		cifs_dbg(FYI, "%s: reached max cache size (%d)\n", __func__, CACHE_MAX_ENTRIES);

		remove_oldest_entry_locked();

	}



	rc = add_cache_entry_locked(refs, numrefs);

	if (!rc)

		atomic_inc(&cache_count);



out_unlock:

	up_write(&htable_rw_lock);
@@ -1313,15 +1323,43 @@ static void refresh_mounts(struct cifs_ses **sessions) 


	list_for_each_entry_safe(tcon, ntcon, &tcons, ulist) {

		const char *path = tcon->dfs_path + 1;

		struct cache_entry *ce;

		struct dfs_info3_param *refs = NULL;

		int numrefs = 0;

		bool needs_refresh = false;

		int rc = 0;



		list_del_init(&tcon->ulist);



		ses = find_ipc_from_server_path(sessions, path);

		if (!IS_ERR(ses)) {

		if (IS_ERR(ses))

			goto next_tcon;



		down_read(&htable_rw_lock);

		ce = lookup_cache_entry(path);

		needs_refresh = IS_ERR(ce) || cache_entry_expired(ce);

		up_read(&htable_rw_lock);



		if (!needs_refresh)

			goto next_tcon;



		xid = get_xid();

			cache_refresh_path(xid, ses, path);

		rc = get_dfs_referral(xid, ses, path, &refs, &numrefs);

		free_xid(xid);



		/* Create or update a cache entry with the new referral */

		if (!rc) {

			down_write(&htable_rw_lock);

			ce = lookup_cache_entry(path);

			if (IS_ERR(ce))

				add_cache_entry_locked(refs, numrefs);

			else if (cache_entry_expired(ce))

				update_cache_entry_locked(ce, refs, numrefs);

			up_write(&htable_rw_lock);

		}



next_tcon:

		free_dfs_info_array(refs, numrefs);

		cifs_put_tcon(tcon);

	}

}
@@ -1331,41 +1369,68 @@ static void refresh_cache(struct cifs_ses **sessions) 
	int i;

	struct cifs_ses *ses;

	unsigned int xid;

	int rc;

	char *ref_paths[CACHE_MAX_ENTRIES];

	int count = 0;

	struct cache_entry *ce;



	/*

	 * Refresh all cached entries.

	 * Refresh all cached entries.  Get all new referrals outside critical section to avoid

	 * starvation while performing SMB2 IOCTL on broken or slow connections.



	 * The cache entries may cover more paths than the active mounts

	 * (e.g. domain-based DFS referrals or multi tier DFS setups).

	 */

	down_write(&htable_rw_lock);

	down_read(&htable_rw_lock);

	for (i = 0; i < CACHE_HTABLE_SIZE; i++) {

		struct cache_entry *ce;

		struct hlist_head *l = &cache_htable[i];



		hlist_for_each_entry(ce, l, hlist) {

			if (count == ARRAY_SIZE(ref_paths))

				goto out_unlock;

			if (hlist_unhashed(&ce->hlist) || !cache_entry_expired(ce) ||

			    IS_ERR(find_ipc_from_server_path(sessions, ce->path)))

				continue;

			ref_paths[count++] = kstrdup(ce->path, GFP_ATOMIC);

		}

	}



out_unlock:

	up_read(&htable_rw_lock);



	for (i = 0; i < count; i++) {

		char *path = ref_paths[i];

		struct dfs_info3_param *refs = NULL;

		int numrefs = 0;

		int rc = 0;



			if (hlist_unhashed(&ce->hlist) || !cache_entry_expired(ce))

		if (!path)

			continue;



			ses = find_ipc_from_server_path(sessions, ce->path);

		ses = find_ipc_from_server_path(sessions, path);

		if (IS_ERR(ses))

				continue;

			goto next_referral;



		xid = get_xid();

			rc = get_dfs_referral(xid, ses, ce->path, &refs, &numrefs);

		rc = get_dfs_referral(xid, ses, path, &refs, &numrefs);

		free_xid(xid);



			if (!rc)

				update_cache_entry_locked(ce->path, refs, numrefs);

		if (!rc) {

			down_write(&htable_rw_lock);

			ce = lookup_cache_entry(path);

			/*

			 * We need to re-check it because other tasks might have it deleted or

			 * updated.

			 */

			if (!IS_ERR(ce) && cache_entry_expired(ce))

				update_cache_entry_locked(ce, refs, numrefs);

			up_write(&htable_rw_lock);

		}



next_referral:

		kfree(path);

		free_dfs_info_array(refs, numrefs);

	}

}

	up_write(&htable_rw_lock);

}



/*

 * Worker that will refresh DFS cache and active mounts based on lowest TTL value from a DFS