pstore: Convert "records_list" locking to mutex

The pstorefs internal list lock doesn't need to be a spinlock and will
create problems when trying to access the list in the subsequent patch
that will walk the pstorefs records during pstore_unregister(). Change
this to a mutex to avoid may_sleep() warnings when unregistering devices.

Link: https://lore.kernel.org/lkml/20200506152114.50375-6-keescook@chromium.org/
Signed-off-by: Kees Cook <keescook@chromium.org>

fs/pstore/inode.c

@@ -22,14 +22,13 @@
 #include <linux/magic.h>
 #include <linux/pstore.h>
 #include <linux/slab.h>
-#include <linux/spinlock.h>
 #include <linux/uaccess.h>
 
 #include "internal.h"
 
 #define	PSTORE_NAMELEN	64
 
-static DEFINE_SPINLOCK(records_list_lock);
+static DEFINE_MUTEX(records_list_lock);
 static LIST_HEAD(records_list);
 
 struct pstore_private {
@@ -192,13 +191,12 @@ static int pstore_unlink(struct inode *dir, struct dentry *dentry)
 static void pstore_evict_inode(struct inode *inode)
 {
 	struct pstore_private	*p = inode->i_private;
-	unsigned long		flags;
 
 	clear_inode(inode);
 	if (p) {
-		spin_lock_irqsave(&records_list_lock, flags);
+		mutex_lock(&records_list_lock);
 		list_del(&p->list);
-		spin_unlock_irqrestore(&records_list_lock, flags);
+		mutex_unlock(&records_list_lock);
 		free_pstore_private(p);
 	}
 }
@@ -297,12 +295,11 @@ int pstore_mkfile(struct dentry *root, struct pstore_record *record)
 	int			rc = 0;
 	char			name[PSTORE_NAMELEN];
 	struct pstore_private	*private, *pos;
-	unsigned long		flags;
 	size_t			size = record->size + record->ecc_notice_size;
 
 	WARN_ON(!inode_is_locked(d_inode(root)));
 
-	spin_lock_irqsave(&records_list_lock, flags);
+	mutex_lock(&records_list_lock);
 	list_for_each_entry(pos, &records_list, list) {
 		if (pos->record->type == record->type &&
 		    pos->record->id == record->id &&
@@ -311,7 +308,7 @@ int pstore_mkfile(struct dentry *root, struct pstore_record *record)
 			break;
 		}
 	}
-	spin_unlock_irqrestore(&records_list_lock, flags);
+	mutex_unlock(&records_list_lock);
 	if (rc)
 		return rc;
 
@@ -343,9 +340,9 @@ int pstore_mkfile(struct dentry *root, struct pstore_record *record)
 
 	d_add(dentry, inode);
 
-	spin_lock_irqsave(&records_list_lock, flags);
+	mutex_lock(&records_list_lock);
 	list_add(&private->list, &records_list);
-	spin_unlock_irqrestore(&records_list_lock, flags);
+	mutex_unlock(&records_list_lock);
 
 	return 0;