s390/debug: fix debug area life cycle

[ Upstream commit 9372a82892c2caa6bccab9a4081166fa769699f8 ]

Currently allocation and registration of s390dbf debug areas are tied
together. As a result, a debug area cannot be unregistered and
re-registered while any process has an associated debugfs file open.

Fix this by splitting alloc/release from register/unregister.

Signed-off-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/s390/kernel/debug.c b/arch/s390/kernel/debug.c
index e392d3e..89fbfb3 100644 (file)
--- a/arch/s390/kernel/debug.c
+++ b/arch/s390/kernel/debug.c
@@ -314,24 +314,6 @@ static debug_info_t *debug_info_create(const char *name, int pages_per_area,
                goto out;
 
        rc->mode = mode & ~S_IFMT;
-
-       /* create root directory */
-       rc->debugfs_root_entry = debugfs_create_dir(rc->name,
-                                                   debug_debugfs_root_entry);
-
-       /* append new element to linked list */
-       if (!debug_area_first) {
-               /* first element in list */
-               debug_area_first = rc;
-               rc->prev = NULL;
-       } else {
-               /* append element to end of list */
-               debug_area_last->next = rc;
-               rc->prev = debug_area_last;
-       }
-       debug_area_last = rc;
-       rc->next = NULL;
-
        refcount_set(&rc->ref_count, 1);
 out:
        return rc;
@@ -391,27 +373,10 @@ static void debug_info_get(debug_info_t *db_info)
  */
 static void debug_info_put(debug_info_t *db_info)
 {
-       int i;
-
        if (!db_info)
                return;
-       if (refcount_dec_and_test(&db_info->ref_count)) {
-               for (i = 0; i < DEBUG_MAX_VIEWS; i++) {
-                       if (!db_info->views[i])
-                               continue;
-                       debugfs_remove(db_info->debugfs_entries[i]);
-               }
-               debugfs_remove(db_info->debugfs_root_entry);
-               if (db_info == debug_area_first)
-                       debug_area_first = db_info->next;
-               if (db_info == debug_area_last)
-                       debug_area_last = db_info->prev;
-               if (db_info->prev)
-                       db_info->prev->next = db_info->next;
-               if (db_info->next)
-                       db_info->next->prev = db_info->prev;
+       if (refcount_dec_and_test(&db_info->ref_count))
                debug_info_free(db_info);
-       }
 }
 
 /*
@@ -635,6 +600,31 @@ static int debug_close(struct inode *inode, struct file *file)
        return 0; /* success */
 }
 
+/* Create debugfs entries and add to internal list. */
+static void _debug_register(debug_info_t *id)
+{
+       /* create root directory */
+       id->debugfs_root_entry = debugfs_create_dir(id->name,
+                                                   debug_debugfs_root_entry);
+
+       /* append new element to linked list */
+       if (!debug_area_first) {
+               /* first element in list */
+               debug_area_first = id;
+               id->prev = NULL;
+       } else {
+               /* append element to end of list */
+               debug_area_last->next = id;
+               id->prev = debug_area_last;
+       }
+       debug_area_last = id;
+       id->next = NULL;
+
+       debug_register_view(id, &debug_level_view);
+       debug_register_view(id, &debug_flush_view);
+       debug_register_view(id, &debug_pages_view);
+}
+
 /**
  * debug_register_mode() - creates and initializes debug area.
  *
@@ -664,19 +654,16 @@ debug_info_t *debug_register_mode(const char *name, int pages_per_area,
        if ((uid != 0) || (gid != 0))
                pr_warn("Root becomes the owner of all s390dbf files in sysfs\n");
        BUG_ON(!initialized);
-       mutex_lock(&debug_mutex);
 
        /* create new debug_info */
        rc = debug_info_create(name, pages_per_area, nr_areas, buf_size, mode);
-       if (!rc)
-               goto out;
-       debug_register_view(rc, &debug_level_view);
-       debug_register_view(rc, &debug_flush_view);
-       debug_register_view(rc, &debug_pages_view);
-out:
-       if (!rc)
+       if (rc) {
+               mutex_lock(&debug_mutex);
+               _debug_register(rc);
+               mutex_unlock(&debug_mutex);
+       } else {
                pr_err("Registering debug feature %s failed\n", name);
-       mutex_unlock(&debug_mutex);
+       }
        return rc;
 }
 EXPORT_SYMBOL(debug_register_mode);
@@ -705,6 +692,27 @@ debug_info_t *debug_register(const char *name, int pages_per_area,
 }
 EXPORT_SYMBOL(debug_register);
 
+/* Remove debugfs entries and remove from internal list. */
+static void _debug_unregister(debug_info_t *id)
+{
+       int i;
+
+       for (i = 0; i < DEBUG_MAX_VIEWS; i++) {
+               if (!id->views[i])
+                       continue;
+               debugfs_remove(id->debugfs_entries[i]);
+       }
+       debugfs_remove(id->debugfs_root_entry);
+       if (id == debug_area_first)
+               debug_area_first = id->next;
+       if (id == debug_area_last)
+               debug_area_last = id->prev;
+       if (id->prev)
+               id->prev->next = id->next;
+       if (id->next)
+               id->next->prev = id->prev;
+}
+
 /**
  * debug_unregister() - give back debug area.
  *
@@ -718,8 +726,10 @@ void debug_unregister(debug_info_t *id)
        if (!id)
                return;
        mutex_lock(&debug_mutex);
-       debug_info_put(id);
+       _debug_unregister(id);
        mutex_unlock(&debug_mutex);
+
+       debug_info_put(id);
 }
 EXPORT_SYMBOL(debug_unregister);