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cifs: avoid potential races when handling multiple dfs tcons
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Now that a DFS tcon manages its own list of DFS referrals and
sessions, there is no point in having a single worker to refresh
referrals of all DFS tcons.  Make it faster and less prone to race
conditions when having several mounts by queueing a worker per DFS
tcon that will take care of refreshing only the DFS referrals related
to it.

Cc: stable@vger.kernel.org # v6.2+
Signed-off-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
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Paulo Alcantara authored and Steve French committed May 4, 2023
1 parent 3dc9c43 commit 6be2ea3
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Showing 5 changed files with 80 additions and 79 deletions.
2 changes: 1 addition & 1 deletion fs/cifs/cifsglob.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1238,8 +1238,8 @@ struct cifs_tcon {
struct cached_fids *cfids;
/* BB add field for back pointer to sb struct(s)? */
#ifdef CONFIG_CIFS_DFS_UPCALL
struct list_head ulist; /* cache update list */
struct list_head dfs_ses_list;
struct delayed_work dfs_cache_work;
#endif
struct delayed_work query_interfaces; /* query interfaces workqueue job */
};
Expand Down
7 changes: 6 additions & 1 deletion fs/cifs/connect.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2340,6 +2340,9 @@ cifs_put_tcon(struct cifs_tcon *tcon)

/* cancel polling of interfaces */
cancel_delayed_work_sync(&tcon->query_interfaces);
#ifdef CONFIG_CIFS_DFS_UPCALL
cancel_delayed_work_sync(&tcon->dfs_cache_work);
#endif

if (tcon->use_witness) {
int rc;
Expand Down Expand Up @@ -2587,7 +2590,9 @@ cifs_get_tcon(struct cifs_ses *ses, struct smb3_fs_context *ctx)
queue_delayed_work(cifsiod_wq, &tcon->query_interfaces,
(SMB_INTERFACE_POLL_INTERVAL * HZ));
}

#ifdef CONFIG_CIFS_DFS_UPCALL
INIT_DELAYED_WORK(&tcon->dfs_cache_work, dfs_cache_refresh);
#endif
spin_lock(&cifs_tcp_ses_lock);
list_add(&tcon->tcon_list, &ses->tcon_list);
spin_unlock(&cifs_tcp_ses_lock);
Expand Down
4 changes: 4 additions & 0 deletions fs/cifs/dfs.c
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Original file line number Diff line number Diff line change
Expand Up @@ -157,6 +157,8 @@ static int get_dfs_conn(struct cifs_mount_ctx *mnt_ctx, const char *ref_path, co
rc = cifs_is_path_remote(mnt_ctx);
}

dfs_cache_noreq_update_tgthint(ref_path + 1, tit);

if (rc == -EREMOTE && is_refsrv) {
rc2 = get_root_smb_session(mnt_ctx);
if (rc2)
Expand Down Expand Up @@ -259,6 +261,8 @@ static int __dfs_mount_share(struct cifs_mount_ctx *mnt_ctx)
if (list_empty(&tcon->dfs_ses_list)) {
list_replace_init(&mnt_ctx->dfs_ses_list,
&tcon->dfs_ses_list);
queue_delayed_work(dfscache_wq, &tcon->dfs_cache_work,
dfs_cache_get_ttl() * HZ);
} else {
dfs_put_root_smb_sessions(&mnt_ctx->dfs_ses_list);
}
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137 changes: 60 additions & 77 deletions fs/cifs/dfs_cache.c
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Original file line number Diff line number Diff line change
Expand Up @@ -20,12 +20,14 @@
#include "cifs_unicode.h"
#include "smb2glob.h"
#include "dns_resolve.h"
#include "dfs.h"

#include "dfs_cache.h"

#define CACHE_HTABLE_SIZE 32
#define CACHE_MAX_ENTRIES 64
#define CACHE_MIN_TTL 120 /* 2 minutes */
#define CACHE_HTABLE_SIZE 32
#define CACHE_MAX_ENTRIES 64
#define CACHE_MIN_TTL 120 /* 2 minutes */
#define CACHE_DEFAULT_TTL 300 /* 5 minutes */

#define IS_DFS_INTERLINK(v) (((v) & DFSREF_REFERRAL_SERVER) && !((v) & DFSREF_STORAGE_SERVER))

Expand All @@ -50,10 +52,9 @@ struct cache_entry {
};

static struct kmem_cache *cache_slab __read_mostly;
static struct workqueue_struct *dfscache_wq __read_mostly;
struct workqueue_struct *dfscache_wq;

static int cache_ttl;
static DEFINE_SPINLOCK(cache_ttl_lock);
atomic_t dfs_cache_ttl;

static struct nls_table *cache_cp;

Expand All @@ -65,10 +66,6 @@ static atomic_t cache_count;
static struct hlist_head cache_htable[CACHE_HTABLE_SIZE];
static DECLARE_RWSEM(htable_rw_lock);

static void refresh_cache_worker(struct work_struct *work);

static DECLARE_DELAYED_WORK(refresh_task, refresh_cache_worker);

/**
* dfs_cache_canonical_path - get a canonical DFS path
*
Expand Down Expand Up @@ -290,7 +287,9 @@ int dfs_cache_init(void)
int rc;
int i;

dfscache_wq = alloc_workqueue("cifs-dfscache", WQ_FREEZABLE | WQ_UNBOUND, 1);
dfscache_wq = alloc_workqueue("cifs-dfscache",
WQ_UNBOUND|WQ_FREEZABLE|WQ_MEM_RECLAIM,
0);
if (!dfscache_wq)
return -ENOMEM;

Expand All @@ -306,6 +305,7 @@ int dfs_cache_init(void)
INIT_HLIST_HEAD(&cache_htable[i]);

atomic_set(&cache_count, 0);
atomic_set(&dfs_cache_ttl, CACHE_DEFAULT_TTL);
cache_cp = load_nls("utf8");
if (!cache_cp)
cache_cp = load_nls_default();
Expand Down Expand Up @@ -480,6 +480,7 @@ static struct cache_entry *add_cache_entry_locked(struct dfs_info3_param *refs,
int rc;
struct cache_entry *ce;
unsigned int hash;
int ttl;

WARN_ON(!rwsem_is_locked(&htable_rw_lock));

Expand All @@ -496,15 +497,8 @@ static struct cache_entry *add_cache_entry_locked(struct dfs_info3_param *refs,
if (IS_ERR(ce))
return ce;

spin_lock(&cache_ttl_lock);
if (!cache_ttl) {
cache_ttl = ce->ttl;
queue_delayed_work(dfscache_wq, &refresh_task, cache_ttl * HZ);
} else {
cache_ttl = min_t(int, cache_ttl, ce->ttl);
mod_delayed_work(dfscache_wq, &refresh_task, cache_ttl * HZ);
}
spin_unlock(&cache_ttl_lock);
ttl = min_t(int, atomic_read(&dfs_cache_ttl), ce->ttl);
atomic_set(&dfs_cache_ttl, ttl);

hlist_add_head(&ce->hlist, &cache_htable[hash]);
dump_ce(ce);
Expand Down Expand Up @@ -616,7 +610,6 @@ static struct cache_entry *lookup_cache_entry(const char *path)
*/
void dfs_cache_destroy(void)
{
cancel_delayed_work_sync(&refresh_task);
unload_nls(cache_cp);
flush_cache_ents();
kmem_cache_destroy(cache_slab);
Expand Down Expand Up @@ -1142,6 +1135,7 @@ static bool target_share_equal(struct TCP_Server_Info *server, const char *s1, c
* target shares in @refs.
*/
static void mark_for_reconnect_if_needed(struct TCP_Server_Info *server,
const char *path,
struct dfs_cache_tgt_list *old_tl,
struct dfs_cache_tgt_list *new_tl)
{
Expand All @@ -1153,22 +1147,39 @@ static void mark_for_reconnect_if_needed(struct TCP_Server_Info *server,
nit = dfs_cache_get_next_tgt(new_tl, nit)) {
if (target_share_equal(server,
dfs_cache_get_tgt_name(oit),
dfs_cache_get_tgt_name(nit)))
dfs_cache_get_tgt_name(nit))) {
dfs_cache_noreq_update_tgthint(path, nit);
return;
}
}
}

cifs_dbg(FYI, "%s: no cached or matched targets. mark dfs share for reconnect.\n", __func__);
cifs_signal_cifsd_for_reconnect(server, true);
}

static bool is_ses_good(struct cifs_ses *ses)
{
struct TCP_Server_Info *server = ses->server;
struct cifs_tcon *tcon = ses->tcon_ipc;
bool ret;

spin_lock(&ses->ses_lock);
spin_lock(&ses->chan_lock);
ret = !cifs_chan_needs_reconnect(ses, server) &&
ses->ses_status == SES_GOOD &&
!tcon->need_reconnect;
spin_unlock(&ses->chan_lock);
spin_unlock(&ses->ses_lock);
return ret;
}

/* Refresh dfs referral of tcon and mark it for reconnect if needed */
static int __refresh_tcon(const char *path, struct cifs_tcon *tcon, bool force_refresh)
static int __refresh_tcon(const char *path, struct cifs_ses *ses, bool force_refresh)
{
struct dfs_cache_tgt_list old_tl = DFS_CACHE_TGT_LIST_INIT(old_tl);
struct dfs_cache_tgt_list new_tl = DFS_CACHE_TGT_LIST_INIT(new_tl);
struct cifs_ses *ses = CIFS_DFS_ROOT_SES(tcon->ses);
struct cifs_tcon *ipc = ses->tcon_ipc;
struct TCP_Server_Info *server = ses->server;
bool needs_refresh = false;
struct cache_entry *ce;
unsigned int xid;
Expand All @@ -1190,20 +1201,19 @@ static int __refresh_tcon(const char *path, struct cifs_tcon *tcon, bool force_r
goto out;
}

spin_lock(&ipc->tc_lock);
if (ipc->status != TID_GOOD) {
spin_unlock(&ipc->tc_lock);
cifs_dbg(FYI, "%s: skip cache refresh due to disconnected ipc\n", __func__);
ses = CIFS_DFS_ROOT_SES(ses);
if (!is_ses_good(ses)) {
cifs_dbg(FYI, "%s: skip cache refresh due to disconnected ipc\n",
__func__);
goto out;
}
spin_unlock(&ipc->tc_lock);

ce = cache_refresh_path(xid, ses, path, true);
if (!IS_ERR(ce)) {
rc = get_targets(ce, &new_tl);
up_read(&htable_rw_lock);
cifs_dbg(FYI, "%s: get_targets: %d\n", __func__, rc);
mark_for_reconnect_if_needed(tcon->ses->server, &old_tl, &new_tl);
mark_for_reconnect_if_needed(server, path, &old_tl, &new_tl);
}

out:
Expand All @@ -1216,10 +1226,11 @@ static int __refresh_tcon(const char *path, struct cifs_tcon *tcon, bool force_r
static int refresh_tcon(struct cifs_tcon *tcon, bool force_refresh)
{
struct TCP_Server_Info *server = tcon->ses->server;
struct cifs_ses *ses = tcon->ses;

mutex_lock(&server->refpath_lock);
if (server->leaf_fullpath)
__refresh_tcon(server->leaf_fullpath + 1, tcon, force_refresh);
__refresh_tcon(server->leaf_fullpath + 1, ses, force_refresh);
mutex_unlock(&server->refpath_lock);
return 0;
}
Expand Down Expand Up @@ -1263,60 +1274,32 @@ int dfs_cache_remount_fs(struct cifs_sb_info *cifs_sb)
return refresh_tcon(tcon, true);
}

/*
* Worker that will refresh DFS cache from all active mounts based on lowest TTL value
* from a DFS referral.
*/
static void refresh_cache_worker(struct work_struct *work)
/* Refresh all DFS referrals related to DFS tcon */
void dfs_cache_refresh(struct work_struct *work)
{
struct TCP_Server_Info *server;
struct cifs_tcon *tcon, *ntcon;
struct list_head tcons;
struct dfs_root_ses *rses;
struct cifs_tcon *tcon;
struct cifs_ses *ses;

INIT_LIST_HEAD(&tcons);
tcon = container_of(work, struct cifs_tcon, dfs_cache_work.work);
ses = tcon->ses;
server = ses->server;

spin_lock(&cifs_tcp_ses_lock);
list_for_each_entry(server, &cifs_tcp_ses_list, tcp_ses_list) {
spin_lock(&server->srv_lock);
if (!server->leaf_fullpath) {
spin_unlock(&server->srv_lock);
continue;
}
spin_unlock(&server->srv_lock);

list_for_each_entry(ses, &server->smb_ses_list, smb_ses_list) {
if (ses->tcon_ipc) {
ses->ses_count++;
list_add_tail(&ses->tcon_ipc->ulist, &tcons);
}
list_for_each_entry(tcon, &ses->tcon_list, tcon_list) {
if (!tcon->ipc) {
tcon->tc_count++;
list_add_tail(&tcon->ulist, &tcons);
}
}
}
}
spin_unlock(&cifs_tcp_ses_lock);

list_for_each_entry_safe(tcon, ntcon, &tcons, ulist) {
struct TCP_Server_Info *server = tcon->ses->server;

list_del_init(&tcon->ulist);
mutex_lock(&server->refpath_lock);
if (server->leaf_fullpath)
__refresh_tcon(server->leaf_fullpath + 1, ses, false);
mutex_unlock(&server->refpath_lock);

list_for_each_entry(rses, &tcon->dfs_ses_list, list) {
ses = rses->ses;
server = ses->server;
mutex_lock(&server->refpath_lock);
if (server->leaf_fullpath)
__refresh_tcon(server->leaf_fullpath + 1, tcon, false);
__refresh_tcon(server->leaf_fullpath + 1, ses, false);
mutex_unlock(&server->refpath_lock);

if (tcon->ipc)
cifs_put_smb_ses(tcon->ses);
else
cifs_put_tcon(tcon);
}

spin_lock(&cache_ttl_lock);
queue_delayed_work(dfscache_wq, &refresh_task, cache_ttl * HZ);
spin_unlock(&cache_ttl_lock);
queue_delayed_work(dfscache_wq, &tcon->dfs_cache_work,
atomic_read(&dfs_cache_ttl) * HZ);
}
9 changes: 9 additions & 0 deletions fs/cifs/dfs_cache.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,9 @@
#include <linux/uuid.h>
#include "cifsglob.h"

extern struct workqueue_struct *dfscache_wq;
extern atomic_t dfs_cache_ttl;

#define DFS_CACHE_TGT_LIST_INIT(var) { .tl_numtgts = 0, .tl_list = LIST_HEAD_INIT((var).tl_list), }

struct dfs_cache_tgt_list {
Expand Down Expand Up @@ -42,6 +45,7 @@ int dfs_cache_get_tgt_share(char *path, const struct dfs_cache_tgt_iterator *it,
char **prefix);
char *dfs_cache_canonical_path(const char *path, const struct nls_table *cp, int remap);
int dfs_cache_remount_fs(struct cifs_sb_info *cifs_sb);
void dfs_cache_refresh(struct work_struct *work);

static inline struct dfs_cache_tgt_iterator *
dfs_cache_get_next_tgt(struct dfs_cache_tgt_list *tl,
Expand Down Expand Up @@ -89,4 +93,9 @@ dfs_cache_get_nr_tgts(const struct dfs_cache_tgt_list *tl)
return tl ? tl->tl_numtgts : 0;
}

static inline int dfs_cache_get_ttl(void)
{
return atomic_read(&dfs_cache_ttl);
}

#endif /* _CIFS_DFS_CACHE_H */

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