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cifs: avoid starvation when refreshing dfs cache
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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: Paulo Alcantara (SUSE) <[email protected]>
Reviewed-by: Aurelien Aptel <[email protected]>
Signed-off-by: Steve French <[email protected]>
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@pcacjr
pcacjr authored and Steve French committed Jun 21, 2021
1 parent 0d52df8 commit 1023e90
Showing 1 changed file with 105 additions and 40 deletions.
145 changes: 105 additions & 40 deletions fs/cifs/dfs_cache.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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];

Expand Down Expand Up @@ -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;
Expand All @@ -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;
}

Expand Down Expand Up @@ -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;
Expand All @@ -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;
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;

return ses->server->ops->get_dfs_refer(xid, ses, path, refs, numrefs, cache_cp,
NO_MAP_UNI_RSVD);
for (i = 0; i < *numrefs; i++)
convert_delimiter(ref[i].path_name, '\\');
}
return rc;
}

/*
Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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)) {
xid = get_xid();
cache_refresh_path(xid, ses, path);
free_xid(xid);
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();
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);
}
}
Expand All @@ -1331,40 +1369,67 @@ 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) {
struct dfs_info3_param *refs = NULL;
int numrefs = 0;

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

ses = find_ipc_from_server_path(sessions, ce->path);
if (IS_ERR(ses))
continue;
out_unlock:
up_read(&htable_rw_lock);

xid = get_xid();
rc = get_dfs_referral(xid, ses, ce->path, &refs, &numrefs);
free_xid(xid);
for (i = 0; i < count; i++) {
char *path = ref_paths[i];
struct dfs_info3_param *refs = NULL;
int numrefs = 0;
int rc = 0;

if (!rc)
update_cache_entry_locked(ce->path, refs, numrefs);
if (!path)
continue;

free_dfs_info_array(refs, numrefs);
ses = find_ipc_from_server_path(sessions, path);
if (IS_ERR(ses))
goto next_referral;

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

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);
}

/*
Expand Down

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