vfs: Add support to debug umount failures

When umount of a partition fails with EBUSY there is
no indication as to what is keeping the mount point busy.

Add support to print a kernel log showing what files
are open on this mount point.

Also add a new new config option CONFIG_FILE_TABLE_DEBUG to
enable this feature.

Change-Id: Id7a3f5e7291b22ffd0f265848ec0a9757f713561
Signed-off-by: Nikhilesh Reddy <reddyn@codeaurora.org>
Signed-off-by: Ankit Jain <ankijain@codeaurora.org>

fs/Kconfig

@@ -309,4 +309,9 @@ endif # NETWORK_FILESYSTEMS
 source "fs/nls/Kconfig"
 source "fs/dlm/Kconfig"
 
+config FILE_TABLE_DEBUG
+	bool "Enable FILE_TABLE_DEBUG"
+	help
+	  This option enables debug of the open files using a global filetable
+
 endmenu

fs/file_table.c

@@ -42,6 +42,141 @@ static struct kmem_cache *filp_cachep __read_mostly;
 
 static struct percpu_counter nr_files __cacheline_aligned_in_smp;
 
+#ifdef CONFIG_FILE_TABLE_DEBUG
+#include <linux/hashtable.h>
+#include <mount.h>
+static DEFINE_MUTEX(global_files_lock);
+static DEFINE_HASHTABLE(global_files_hashtable, 10);
+
+struct global_filetable_lookup_key {
+	struct work_struct work;
+	uintptr_t value;
+};
+
+void global_filetable_print_warning_once(void)
+{
+	pr_err_once("\n**********************************************************\n");
+	pr_err_once("**   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   **\n");
+	pr_err_once("**                                                      **\n");
+	pr_err_once("**      VFS FILE TABLE DEBUG is enabled .               **\n");
+	pr_err_once("**  Allocating extra memory and slowing access to files **\n");
+	pr_err_once("**                                                      **\n");
+	pr_err_once("** This means that this is a DEBUG kernel and it is     **\n");
+	pr_err_once("** unsafe for production use.                           **\n");
+	pr_err_once("**                                                      **\n");
+	pr_err_once("** If you see this message and you are not debugging    **\n");
+	pr_err_once("** the kernel, report this immediately to your vendor!  **\n");
+	pr_err_once("**                                                      **\n");
+	pr_err_once("**   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   **\n");
+	pr_err_once("**********************************************************\n");
+}
+
+void global_filetable_add(struct file *filp)
+{
+	struct mount *mnt;
+
+	if (filp->f_path.dentry->d_iname == NULL ||
+	    strlen(filp->f_path.dentry->d_iname) == 0)
+		return;
+
+	mnt = real_mount(filp->f_path.mnt);
+
+	mutex_lock(&global_files_lock);
+	hash_add(global_files_hashtable, &filp->f_hash, (uintptr_t)mnt);
+	mutex_unlock(&global_files_lock);
+}
+
+void global_filetable_del(struct file *filp)
+{
+	mutex_lock(&global_files_lock);
+	hash_del(&filp->f_hash);
+	mutex_unlock(&global_files_lock);
+}
+
+static void global_print_file(struct file *filp, char *path_buffer, int *count)
+{
+	char *pathname;
+
+	pathname = d_path(&filp->f_path, path_buffer, PAGE_SIZE);
+	if (IS_ERR(pathname))
+		pr_err("VFS: File %d Address : %pa partial filename: %s ref_count=%ld\n",
+			++(*count), &filp, filp->f_path.dentry->d_iname,
+			atomic_long_read(&filp->f_count));
+	else
+		pr_err("VFS: File %d Address : %pa full filepath: %s ref_count=%ld\n",
+			++(*count), &filp, pathname,
+			atomic_long_read(&filp->f_count));
+}
+
+static void global_filetable_print(uintptr_t lookup_mnt)
+{
+	struct hlist_node *tmp;
+	struct file *filp;
+	struct mount *mnt;
+	int index;
+	int count = 0;
+	char *path_buffer = (char *)__get_free_page(GFP_KERNEL);
+
+	mutex_lock(&global_files_lock);
+	pr_err("\n**********************************************************\n");
+	pr_err("**   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   **\n");
+
+	pr_err("\n");
+	pr_err("VFS: The following files hold a reference to the mount\n");
+	pr_err("\n");
+	hash_for_each_possible_safe(global_files_hashtable, filp, tmp, f_hash,
+				    lookup_mnt) {
+		mnt = real_mount(filp->f_path.mnt);
+		if ((uintptr_t)mnt == lookup_mnt)
+			global_print_file(filp, path_buffer, &count);
+	}
+	pr_err("\n");
+	pr_err("VFS: Found total of %d open files\n", count);
+	pr_err("\n");
+
+	count = 0;
+	pr_err("\n");
+	pr_err("VFS: The following files need to cleaned up\n");
+	pr_err("\n");
+	hash_for_each_safe(global_files_hashtable, index, tmp, filp, f_hash) {
+		if (atomic_long_read(&filp->f_count) == 0)
+			global_print_file(filp, path_buffer, &count);
+	}
+
+	pr_err("\n");
+	pr_err("VFS: Found total of %d files awaiting clean-up\n", count);
+	pr_err("\n");
+	pr_err("**   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   **\n");
+	pr_err("\n**********************************************************\n");
+
+	mutex_unlock(&global_files_lock);
+	free_page((unsigned long)path_buffer);
+}
+
+static void global_filetable_print_work_fn(struct work_struct *work)
+{
+	struct global_filetable_lookup_key *key;
+	uintptr_t lookup_mnt;
+
+	key = container_of(work, struct global_filetable_lookup_key, work);
+	lookup_mnt = key->value;
+	kfree(key);
+	global_filetable_print(lookup_mnt);
+}
+
+void global_filetable_delayed_print(struct mount *mnt)
+{
+	struct global_filetable_lookup_key *key;
+
+	key = kzalloc(sizeof(*key), GFP_KERNEL);
+	if (key == NULL)
+		return;
+	key->value = (uintptr_t)mnt;
+	INIT_WORK(&key->work, global_filetable_print_work_fn);
+	schedule_work(&key->work);
+}
+#endif /* CONFIG_FILE_TABLE_DEBUG */
+
 static void file_free_rcu(struct rcu_head *head)
 {
 	struct file *f = container_of(head, struct file, f_u.fu_rcuhead);
@@ -221,6 +356,7 @@ static void __fput(struct file *file)
 		put_write_access(inode);
 		__mnt_drop_write(mnt);
 	}
+	global_filetable_del(file);
 	file->f_path.dentry = NULL;
 	file->f_path.mnt = NULL;
 	file->f_inode = NULL;
@@ -320,6 +456,7 @@ void __init files_init(void)
 	filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
 			SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
 	percpu_counter_init(&nr_files, 0, GFP_KERNEL);
+	global_filetable_print_warning_once();
 }
 
 /*

fs/internal.h

@@ -186,3 +186,29 @@ loff_t iomap_apply(struct inode *inode, loff_t pos, loff_t length,
 
 /* direct-io.c: */
 int sb_init_dio_done_wq(struct super_block *sb);
+
+#ifdef CONFIG_FILE_TABLE_DEBUG
+void global_filetable_print_warning_once(void);
+void global_filetable_add(struct file *filp);
+void global_filetable_del(struct file *filp);
+void global_filetable_delayed_print(struct mount *mnt);
+
+#else /* i.e NOT CONFIG_FILE_TABLE_DEBUG */
+
+static inline void global_filetable_print_warning_once(void)
+{
+}
+
+static inline void global_filetable_add(struct file *filp)
+{
+}
+
+static inline void global_filetable_del(struct file *filp)
+{
+}
+
+static inline void global_filetable_delayed_print(struct mount *mnt)
+{
+}
+
+#endif /* CONFIG_FILE_TABLE_DEBUG */

fs/namei.c

@@ -3573,6 +3573,8 @@ out2:
 				error = -ESTALE;
 		}
 		file = ERR_PTR(error);
+	} else {
+		global_filetable_add(file);
 	}
 	return file;
 }

fs/namespace.c

@@ -1668,6 +1668,8 @@ static int do_umount(struct mount *mnt, int flags)
 	}
 	unlock_mount_hash();
 	namespace_unlock();
+	if (retval == -EBUSY)
+		global_filetable_delayed_print(mnt);
 	return retval;
 }
 

include/linux/fs.h

@@ -887,6 +887,9 @@ struct file {
 #endif /* #ifdef CONFIG_EPOLL */
 	struct address_space	*f_mapping;
 	errseq_t		f_wb_err;
+#ifdef CONFIG_FILE_TABLE_DEBUG
+	struct hlist_node f_hash;
+#endif /* #ifdef CONFIG_FILE_TABLE_DEBUG */
 } __randomize_layout
   __attribute__((aligned(4)));	/* lest something weird decides that 2 is OK */