smb: client: fix (remove) drop_dir_cache module parameter

Being a module parameter, it's possible to do:

  # modprobe cifs drop_dir_cache=1

Which will lead to a crash, because cifs_tcp_ses_list hasn't been
initialized yet:

  [  168.242624] BUG: kernel NULL pointer dereference, address: 0000000000000010
  [  168.242952] #PF: supervisor read access in kernel mode
  [  168.243175] #PF: error_code(0x0000) - not-present page
  [  168.243394] PGD 0 P4D 0
  [  168.243524] Oops: Oops: 0000 [#1] SMP NOPTI
  [  168.243703] CPU: 2 UID: 0 PID: 1105 Comm: modprobe Not tainted 7.0.0-lku #5 PREEMPT(lazy)
  [  168.244054] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.17.0-2-g4f253b9b-prebuilt.qemu.org 04/01/2014
  [  168.244557] RIP: 0010:cifs_param_set_drop_dir_cache+0x7c/0x100 [cifs]
  ...
  [  168.248785] Call Trace:
  [  168.248915]  <TASK>
  [  168.249023]  parse_args+0x285/0x3a0
  [  168.249204]  ? __pfx_unknown_module_param_cb+0x10/0x10
  [  168.249448]  load_module+0x192b/0x1bb0
  [  168.249637]  ? __pfx_unknown_module_param_cb+0x10/0x10
  [  168.249882]  ? kernel_read_file+0x27d/0x2b0
  [  168.250088]  init_module_from_file+0xce/0xf0
  [  168.250291]  idempotent_init_module+0xfb/0x2f0
  [  168.250496]  __x64_sys_finit_module+0x5a/0xa0
  [  168.250694]  do_syscall_64+0xe0/0x5a0
  [  168.250863]  ? exc_page_fault+0x65/0x160
  [  168.251050]  entry_SYSCALL_64_after_hwframe+0x77/0x7f
  [  168.251284] RIP: 0033:0x7fcaa12b774d

Instead of fixing this with some kind of "is module initialized"
approach, this patch instead moves that functionality to procfs,
setting a write op for the existing open_dirs entry, where
writing a 0 to it will drop the cached directory entries.

Also make it available only when CONFIG_CIFS_DEBUG=y.

A small change needed now is to not call flush_delayed_work()
on invalidate_all_cached_dirs() when called from procfs (can't sleep in
that context).
So add a @sync arg to invalidate_all_cached_dirs() to control when to
flush the delayed works.

Fixes: dde6667fa3c8 ("smb: client: add drop_dir_cache module parameter to invalidate cached dirents")
Signed-off-by: Enzo Matsumiya <ematsumiya@suse.de>
Signed-off-by: Steve French <stfrench@microsoft.com>

6 files changed, 59 insertions, 45 deletions

diff --git a/fs/smb/client/cached_dir.c b/fs/smb/client/cached_dir.c
index 04bb95091f49..02791ec3c5a1 100644
--- a/fs/smb/client/cached_dir.c
+++ b/fs/smb/client/cached_dir.c
@@ -593,7 +593,7 @@ done:
  * Invalidate all cached dirs when a TCON has been reset
  * due to a session loss.
  */
-void invalidate_all_cached_dirs(struct cifs_tcon *tcon)
+void invalidate_all_cached_dirs(struct cifs_tcon *tcon, bool sync)
 {
 	struct cached_fids *cfids = tcon->cfids;
 	struct cached_fid *cfid, *q;
@@ -625,7 +625,8 @@ void invalidate_all_cached_dirs(struct cifs_tcon *tcon)
 
 	/* run laundromat unconditionally now as there might have been previously queued work */
 	mod_delayed_work(cfid_put_wq, &cfids->laundromat_work, 0);
-	flush_delayed_work(&cfids->laundromat_work);
+	if (sync)
+		flush_delayed_work(&cfids->laundromat_work);
 }
 
 static void
diff --git a/fs/smb/client/cached_dir.h b/fs/smb/client/cached_dir.h
index 19d5592512e4..fc756836da95 100644
--- a/fs/smb/client/cached_dir.h
+++ b/fs/smb/client/cached_dir.h
@@ -90,7 +90,7 @@ void close_cached_dir(struct cached_fid *cfid);
 void drop_cached_dir_by_name(const unsigned int xid, struct cifs_tcon *tcon,
 			     const char *name, struct cifs_sb_info *cifs_sb);
 void close_all_cached_dirs(struct cifs_sb_info *cifs_sb);
-void invalidate_all_cached_dirs(struct cifs_tcon *tcon);
+void invalidate_all_cached_dirs(struct cifs_tcon *tcon, bool sync);
 bool cached_dir_lease_break(struct cifs_tcon *tcon, __u8 lease_key[16]);
 
 #endif			/* _CACHED_DIR_H */
diff --git a/fs/smb/client/cifs_debug.c b/fs/smb/client/cifs_debug.c
index 0691d2a3e04b..4ed4f55a0bb7 100644
--- a/fs/smb/client/cifs_debug.c
+++ b/fs/smb/client/cifs_debug.c
@@ -306,6 +306,9 @@ static int cifs_debug_dirs_proc_show(struct seq_file *m, void *v)
 	LIST_HEAD(entry);
 
 	seq_puts(m, "# Version:1\n");
+#ifdef CONFIG_CIFS_DEBUG
+	seq_puts(m, "# Write 0 to this file to drop all cached directory entries\n");
+#endif /* CONFIG_CIFS_DEBUG */
 	seq_puts(m, "# Format:\n");
 	seq_puts(m, "# <tree id> <sess id> <persistent fid> <lease-key> <path>\n");
 
@@ -353,6 +356,51 @@ static int cifs_debug_dirs_proc_show(struct seq_file *m, void *v)
 	return 0;
 }
 
+#ifdef CONFIG_CIFS_DEBUG
+static int cifs_debug_dirs_proc_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, cifs_debug_dirs_proc_show, NULL);
+}
+
+/* Drop all cached directory entries across all CIFS mounts. */
+static ssize_t cifs_debug_dirs_proc_write(struct file *file, const char __user *buffer,
+					  size_t count, loff_t *ppos)
+{
+	int rc, v;
+
+	rc = kstrtoint_from_user(buffer, count, 10, &v);
+	if (rc)
+		return rc;
+
+	if (v == 0) {
+		struct TCP_Server_Info *server;
+		struct cifs_ses *ses;
+		struct cifs_tcon *tcon;
+
+		spin_lock(&cifs_tcp_ses_lock);
+		list_for_each_entry(server, &cifs_tcp_ses_list, tcp_ses_list) {
+			list_for_each_entry(ses, &server->smb_ses_list, smb_ses_list) {
+				if (cifs_ses_exiting(ses))
+					continue;
+				list_for_each_entry(tcon, &ses->tcon_list, tcon_list)
+					invalidate_all_cached_dirs(tcon, false);
+			}
+		}
+		spin_unlock(&cifs_tcp_ses_lock);
+	}
+
+	return count;
+}
+
+static const struct proc_ops cifs_debug_dirs_proc_ops = {
+	.proc_open	= cifs_debug_dirs_proc_open,
+	.proc_read	= seq_read,
+	.proc_lseek	= seq_lseek,
+	.proc_release	= single_release,
+	.proc_write	= cifs_debug_dirs_proc_write,
+};
+#endif /* CONFIG_CIFS_DEBUG */
+
 static __always_inline const char *compression_alg_str(__le16 alg)
 {
 	switch (alg) {
@@ -885,9 +933,11 @@ cifs_proc_init(void)
 	proc_create_single("open_files", 0400, proc_fs_cifs,
 			cifs_debug_files_proc_show);
 
-	proc_create_single("open_dirs", 0400, proc_fs_cifs,
-			cifs_debug_dirs_proc_show);
-
+#ifdef CONFIG_CIFS_DEBUG
+	proc_create("open_dirs", 0600, proc_fs_cifs, &cifs_debug_dirs_proc_ops);
+#else /* CONFIG_CIFS_DEBUG */
+	proc_create_single("open_dirs", 0400, proc_fs_cifs, cifs_debug_dirs_proc_show);
+#endif /* !CONFIG_CIFS_DEBUG */
 	proc_create("Stats", 0644, proc_fs_cifs, &cifs_stats_proc_ops);
 	proc_create("cifsFYI", 0644, proc_fs_cifs, &cifsFYI_proc_ops);
 	proc_create("traceSMB", 0644, proc_fs_cifs, &traceSMB_proc_ops);
diff --git a/fs/smb/client/cifsfs.c b/fs/smb/client/cifsfs.c
index 2025739f070a..2e92c7fa2c5d 100644
--- a/fs/smb/client/cifsfs.c
+++ b/fs/smb/client/cifsfs.c
@@ -127,43 +127,6 @@ atomic64_t cifs_dircache_bytes_used = ATOMIC64_INIT(0);
 atomic_t cifs_sillycounter;
 atomic_t cifs_tmpcounter;
 
-/*
- * Write-only module parameter to drop all cached directory entries across
- * all CIFS mounts. Echo a non-zero value to trigger.
- */
-static void cifs_drop_all_dir_caches(void)
-{
-	struct TCP_Server_Info *server;
-	struct cifs_ses *ses;
-	struct cifs_tcon *tcon;
-
-	spin_lock(&cifs_tcp_ses_lock);
-	list_for_each_entry(server, &cifs_tcp_ses_list, tcp_ses_list) {
-		list_for_each_entry(ses, &server->smb_ses_list, smb_ses_list) {
-			if (cifs_ses_exiting(ses))
-				continue;
-			list_for_each_entry(tcon, &ses->tcon_list, tcon_list)
-				invalidate_all_cached_dirs(tcon);
-		}
-	}
-	spin_unlock(&cifs_tcp_ses_lock);
-}
-
-static int cifs_param_set_drop_dir_cache(const char *val, const struct kernel_param *kp)
-{
-	bool bv;
-	int rc = kstrtobool(val, &bv);
-
-	if (rc)
-		return rc;
-	if (bv)
-		cifs_drop_all_dir_caches();
-	return 0;
-}
-
-module_param_call(drop_dir_cache, cifs_param_set_drop_dir_cache, NULL, NULL, 0200);
-MODULE_PARM_DESC(drop_dir_cache, "Write 1 to drop all cached directory entries across all CIFS mounts");
-
 #ifdef CONFIG_CIFS_STATS2
 unsigned int slow_rsp_threshold = 1;
 module_param(slow_rsp_threshold, uint, 0644);
diff --git a/fs/smb/client/file.c b/fs/smb/client/file.c
index f743f058667f..664a2c223089 100644
--- a/fs/smb/client/file.c
+++ b/fs/smb/client/file.c
@@ -393,7 +393,7 @@ cifs_mark_open_files_invalid(struct cifs_tcon *tcon)
 	}
 	spin_unlock(&tcon->open_file_lock);
 
-	invalidate_all_cached_dirs(tcon);
+	invalidate_all_cached_dirs(tcon, true);
 	spin_lock(&tcon->tc_lock);
 	if (tcon->status == TID_IN_FILES_INVALIDATE)
 		tcon->status = TID_NEED_TCON;
diff --git a/fs/smb/client/smb2pdu.c b/fs/smb/client/smb2pdu.c
index cd8b49722149..cb61051f9af3 100644
--- a/fs/smb/client/smb2pdu.c
+++ b/fs/smb/client/smb2pdu.c
@@ -2257,7 +2257,7 @@ SMB2_tdis(const unsigned int xid, struct cifs_tcon *tcon)
 	}
 	spin_unlock(&ses->chan_lock);
 
-	invalidate_all_cached_dirs(tcon);
+	invalidate_all_cached_dirs(tcon, true);
 
 	rc = smb2_plain_req_init(SMB2_TREE_DISCONNECT, tcon, server,
 				 (void **) &req,