fs/proc/vmcore: convert vmcore_cb_lock into vmcore_mutex

We want to protect vmcore modifications from concurrent opening of
the vmcore, and also serialize vmcore modification.

(a) We can currently modify the vmcore after it was opened. This can happen
    if a vmcoredd is added after the vmcore module was initialized and
    already opened by user space. We want to fix that and prepare for
    new code wanting to serialize against concurrent opening.

(b) To handle it cleanly we need to protect the modifications against
    concurrent opening. As the modifications end up allocating memory and
    can sleep, we cannot rely on the spinlock.

Let's convert the spinlock into a mutex to prepare for further changes.

Signed-off-by: David Hildenbrand <[email protected]>
Message-Id: <[email protected]>
Acked-by: Andrew Morton <[email protected]>
Signed-off-by: Michael S. Tsirkin <[email protected]>

Author: davidhildenbrand

fs/proc/vmcore.c

@@ -62,7 +62,8 @@ core_param(novmcoredd, vmcoredd_disabled, bool, 0);
 /* Device Dump Size */
 static size_t vmcoredd_orig_sz;
 
-static DEFINE_SPINLOCK(vmcore_cb_lock);
+static DEFINE_MUTEX(vmcore_mutex);
+
 DEFINE_STATIC_SRCU(vmcore_cb_srcu);
 /* List of registered vmcore callbacks. */
 static LIST_HEAD(vmcore_cb_list);
@@ -72,21 +73,21 @@ static bool vmcore_opened;
 void register_vmcore_cb(struct vmcore_cb *cb)
 {
 	INIT_LIST_HEAD(&cb->next);
-	spin_lock(&vmcore_cb_lock);
+	mutex_lock(&vmcore_mutex);
 	list_add_tail(&cb->next, &vmcore_cb_list);
 	/*
 	 * Registering a vmcore callback after the vmcore was opened is
 	 * very unusual (e.g., manual driver loading).
 	 */
 	if (vmcore_opened)
 		pr_warn_once("Unexpected vmcore callback registration\n");
-	spin_unlock(&vmcore_cb_lock);
+	mutex_unlock(&vmcore_mutex);
 }
 EXPORT_SYMBOL_GPL(register_vmcore_cb);
 
 void unregister_vmcore_cb(struct vmcore_cb *cb)
 {
-	spin_lock(&vmcore_cb_lock);
+	mutex_lock(&vmcore_mutex);
 	list_del_rcu(&cb->next);
 	/*
 	 * Unregistering a vmcore callback after the vmcore was opened is
@@ -95,7 +96,7 @@ void unregister_vmcore_cb(struct vmcore_cb *cb)
 	 */
 	if (vmcore_opened)
 		pr_warn_once("Unexpected vmcore callback unregistration\n");
-	spin_unlock(&vmcore_cb_lock);
+	mutex_unlock(&vmcore_mutex);
 
 	synchronize_srcu(&vmcore_cb_srcu);
 }
@@ -120,9 +121,9 @@ static bool pfn_is_ram(unsigned long pfn)
 
 static int open_vmcore(struct inode *inode, struct file *file)
 {
-	spin_lock(&vmcore_cb_lock);
+	mutex_lock(&vmcore_mutex);
 	vmcore_opened = true;
-	spin_unlock(&vmcore_cb_lock);
+	mutex_unlock(&vmcore_mutex);
 
 	return 0;
 }