diff options
author | Paulo Alcantara <pc@cjr.nz> | 2023-01-18 01:00:37 +0300 |
---|---|---|
committer | Steve French <stfrench@microsoft.com> | 2023-01-18 19:45:40 +0300 |
commit | 9fb0db40513e27537fde63287aea920b60557a69 (patch) | |
tree | e76129a7dcf2b7f5ecd5515557e9dfd2d6a2cb7a /fs/cifs/dfs_cache.c | |
parent | 5dc4c995db9eb45f6373a956eb1f69460e69e6d4 (diff) | |
download | linux-9fb0db40513e27537fde63287aea920b60557a69.tar.xz |
cifs: fix potential deadlock in cache_refresh_path()
Avoid getting DFS referral from an exclusive lock in
cache_refresh_path() because the tcon IPC used for getting the
referral could be disconnected and thus causing a deadlock as shown
below:
task A task B
====== ======
cifs_demultiplex_thread() dfs_cache_find()
cifs_handle_standard() cache_refresh_path()
reconnect_dfs_server() down_write()
dfs_cache_noreq_find() get_dfs_referral()
down_read() <- deadlock smb2_get_dfs_refer()
SMB2_ioctl()
cifs_send_recv()
compound_send_recv()
wait_for_response()
where task A cannot wake up task B because it is blocked on
down_read() due to the exclusive lock held in cache_refresh_path() and
therefore not being able to make progress.
Fixes: c9f711039905 ("cifs: keep referral server sessions alive")
Reviewed-by: Aurélien Aptel <aurelien.aptel@gmail.com>
Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Signed-off-by: Steve French <stfrench@microsoft.com>
Diffstat (limited to 'fs/cifs/dfs_cache.c')
-rw-r--r-- | fs/cifs/dfs_cache.c | 42 |
1 files changed, 23 insertions, 19 deletions
diff --git a/fs/cifs/dfs_cache.c b/fs/cifs/dfs_cache.c index e20f8880363f..a6d7ae5f49a4 100644 --- a/fs/cifs/dfs_cache.c +++ b/fs/cifs/dfs_cache.c @@ -770,26 +770,27 @@ static int get_dfs_referral(const unsigned int xid, struct cifs_ses *ses, const */ static int cache_refresh_path(const unsigned int xid, struct cifs_ses *ses, const char *path) { - int rc; - struct cache_entry *ce; struct dfs_info3_param *refs = NULL; + struct cache_entry *ce; int numrefs = 0; - bool newent = false; + int rc; cifs_dbg(FYI, "%s: search path: %s\n", __func__, path); - down_write(&htable_rw_lock); + down_read(&htable_rw_lock); ce = lookup_cache_entry(path); - if (!IS_ERR(ce)) { - if (!cache_entry_expired(ce)) { - dump_ce(ce); - up_write(&htable_rw_lock); - return 0; - } - } else { - newent = true; + if (!IS_ERR(ce) && !cache_entry_expired(ce)) { + up_read(&htable_rw_lock); + return 0; } + /* + * Unlock shared access as we don't want to hold any locks while getting + * a new referral. The @ses used for performing the I/O could be + * reconnecting and it acquires @htable_rw_lock to look up the dfs cache + * in order to failover -- if necessary. + */ + up_read(&htable_rw_lock); /* * Either the entry was not found, or it is expired. @@ -797,19 +798,22 @@ static int cache_refresh_path(const unsigned int xid, struct cifs_ses *ses, cons */ rc = get_dfs_referral(xid, ses, path, &refs, &numrefs); if (rc) - goto out_unlock; + goto out; dump_refs(refs, numrefs); - if (!newent) { - rc = update_cache_entry_locked(ce, refs, numrefs); - goto out_unlock; + down_write(&htable_rw_lock); + /* Re-check as another task might have it added or refreshed already */ + ce = lookup_cache_entry(path); + if (!IS_ERR(ce)) { + if (cache_entry_expired(ce)) + rc = update_cache_entry_locked(ce, refs, numrefs); + } else { + rc = add_cache_entry_locked(refs, numrefs); } - rc = add_cache_entry_locked(refs, numrefs); - -out_unlock: up_write(&htable_rw_lock); +out: free_dfs_info_array(refs, numrefs); return rc; } |