From: Paulo Alcantara pc@cjr.nz
[ Upstream commit 9fb0db40513e27537fde63287aea920b60557a69 ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- fs/cifs/dfs_cache.c | 42 +++++++++++++++++++++++------------------- 1 file changed, 23 insertions(+), 19 deletions(-)
diff --git a/fs/cifs/dfs_cache.c b/fs/cifs/dfs_cache.c index e70915ad7541..4302dc75843c 100644 --- a/fs/cifs/dfs_cache.c +++ b/fs/cifs/dfs_cache.c @@ -792,26 +792,27 @@ 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. @@ -819,19 +820,22 @@ 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; }