[PATCH 2/2] ext4: Handle nested ext4_journal_start/stop calls without a journal

[PATCH 2/2] ext4: Handle nested ext4_journal_start/stop calls without a journal

[Curt Wohlgemuth]

This patch fixes a problem with handling nested calls to
ext4_journal_start/ext4_journal_stop, when there is no journal present.

	Signed-off-by: Curt Wohlgemuth <curtw@google.com>
---

Instead of using the special value of

        (handle_t *)0x1

to represent a handle when there is no journal present, we now use a real
handle_t, so we can use its ref counting.  The h_transaction field now
determines if there is a journal present or not.

Note that ext4_handle_valid() previously returned 1 if a NULL handle was
sent in -- which is a bad use of this routine.  Instead now, we'll get a
NULL pointer dereference...


diff -uprN orig/fs/ext4/ext4_jbd2.h new/fs/ext4/ext4_jbd2.h
--- orig/fs/ext4/ext4_jbd2.h	2009-09-17 14:32:13.000000000 -0700
+++ new/fs/ext4/ext4_jbd2.h	2009-09-17 14:31:01.000000000 -0700
@@ -161,11 +161,11 @@ int __ext4_handle_dirty_metadata(const c
 handle_t *ext4_journal_start_sb(struct super_block *sb, int nblocks);
 int __ext4_journal_stop(const char *where, handle_t *handle);

-#define EXT4_NOJOURNAL_HANDLE	((handle_t *) 0x1)
+#define EXT4_NOJOURNAL_TRANSACTION ((transaction_t *) 0x1)

 static inline int ext4_handle_valid(handle_t *handle)
 {
--	if (handle == EXT4_NOJOURNAL_HANDLE)
+	if (handle->h_transaction == EXT4_NOJOURNAL_TRANSACTION)
 		return 0;
 	return 1;
 }
diff -uprN orig/fs/ext4/inode.c new/fs/ext4/inode.c
--- orig/fs/ext4/inode.c	2009-09-17 14:14:43.000000000 -0700
+++ new/fs/ext4/inode.c	2009-09-17 14:32:58.000000000 -0700
@@ -4931,12 +4931,14 @@ int ext4_write_inode(struct inode *inode
 		err = ext4_force_commit(inode->i_sb);
 	} else {
 		struct ext4_iloc iloc;
+		handle_t *handle = ext4_journal_start(inode, 1);

 		err = ext4_get_inode_loc(inode, &iloc);
 		if (err)
 			return err;
-		err = ext4_do_update_inode(EXT4_NOJOURNAL_HANDLE,
-					   inode, &iloc, wait);
+		err = ext4_do_update_inode(handle, inode, &iloc, wait);
+
+		ext4_journal_stop(handle);
 	}
 	return err;
 }
diff -uprN orig/fs/ext4/namei.c new/fs/ext4/namei.c
--- orig/fs/ext4/namei.c	2009-09-17 14:29:57.000000000 -0700
+++ new/fs/ext4/namei.c	2009-09-17 14:33:06.000000000 -0700
@@ -2076,7 +2076,8 @@ int ext4_orphan_del(handle_t *handle, st
 	struct ext4_iloc iloc;
 	int err = 0;

-	if (!ext4_handle_valid(handle))
+	/* ext4_handle_valid() assumes a valid handle_t pointer */
+	if (handle && !ext4_handle_valid(handle))
 		return 0;

 	mutex_lock(&EXT4_SB(inode->i_sb)->s_orphan_lock);
diff -uprN orig/fs/ext4/super.c new/fs/ext4/super.c
--- orig/fs/ext4/super.c	2009-09-17 14:30:02.000000000 -0700
+++ new/fs/ext4/super.c	2009-09-17 14:33:06.000000000 -0700
@@ -198,6 +198,43 @@ void ext4_itable_unused_set(struct super
 		bg->bg_itable_unused_hi = cpu_to_le16(count >> 16);
 }

+
+/* If the current tasks journal_info is NULL, create a new one, else
+ * bump its ref count */
+static handle_t *ext4_get_nojournal(void)
+{
+	handle_t *handle = current->journal_info;
+
+	if (handle) {
+		BUG_ON(handle->h_transaction != EXT4_NOJOURNAL_TRANSACTION);
+		handle->h_ref++;
+		return handle;
+	}
+
+	handle = jbd2_alloc_handle(GFP_NOFS);
+	if (!handle)
+		return NULL;
+
+	memset(handle, 0, sizeof(*handle));
+	handle->h_ref = 1;
+	handle->h_transaction = EXT4_NOJOURNAL_TRANSACTION;
+
+	current->journal_info = handle;
+	return handle;
+}
+
+
+/* Decrement the ref count, delete if now 0. */
+static void ext4_put_nojournal(handle_t *handle)
+{
+	BUG_ON(handle->h_transaction != EXT4_NOJOURNAL_TRANSACTION);
+	if (--handle->h_ref > 0)
+		return;
+
+	jbd2_free_handle(handle);
+	current->journal_info = NULL;
+}
+
 /*
  * Wrappers for jbd2_journal_start/end.
  *
@@ -224,11 +261,7 @@ handle_t *ext4_journal_start_sb(struct s
 		}
 		return jbd2_journal_start(journal, nblocks);
 	}
-	/*
-	 * We're not journaling, return the appropriate indication.
-	 */
-	current->journal_info = EXT4_NOJOURNAL_HANDLE;
-	return current->journal_info;
+	return ext4_get_nojournal();
 }

 /*
@@ -244,11 +277,7 @@ int __ext4_journal_stop(const char *wher
 	int rc;

 	if (!ext4_handle_valid(handle)) {
-		/*
-		 * Do this here since we don't call jbd2_journal_stop() in
-		 * no-journal mode.
-		 */
-		current->journal_info = NULL;
+		ext4_put_nojournal(handle);
 		return 0;
 	}
 	sb = handle->h_transaction->t_journal->j_private;

Re: [PATCH 2/2] ext4: Handle nested ext4_journal_start/stop calls without a journal

[Andreas Dilger]

On Sep 17, 2009  14:55 -0700, Curt Wohlgemuth wrote:
> This patch fixes a problem with handling nested calls to
> ext4_journal_start/ext4_journal_stop, when there is no journal present.
> 
> 	Signed-off-by: Curt Wohlgemuth <curtw@google.com>
> ---
> 
> Instead of using the special value of
> 
>         (handle_t *)0x1
> 
> to represent a handle when there is no journal present, we now use a real
> handle_t, so we can use its ref counting.  The h_transaction field now
> determines if there is a journal present or not.

You _could_ just use the "handle" value as a refcount, and anything less
than, say, 4096 is considered a "special" handle.  I can't imagine the
refcount being more than 3 or 4 even in extreme cases.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

Re: [PATCH 2/2] ext4: Handle nested ext4_journal_start/stop calls without a journal

[Curt Wohlgemuth]

On Thu, Sep 17, 2009 at 10:50 PM, Andreas Dilger <adilger@sun.com> wrote:
> On Sep 17, 2009  14:55 -0700, Curt Wohlgemuth wrote:
>> This patch fixes a problem with handling nested calls to
>> ext4_journal_start/ext4_journal_stop, when there is no journal present.
>>
>>       Signed-off-by: Curt Wohlgemuth <curtw@google.com>
>> ---
>>
>> Instead of using the special value of
>>
>>         (handle_t *)0x1
>>
>> to represent a handle when there is no journal present, we now use a real
>> handle_t, so we can use its ref counting.  The h_transaction field now
>> determines if there is a journal present or not.
>
> You _could_ just use the "handle" value as a refcount, and anything less
> than, say, 4096 is considered a "special" handle.  I can't imagine the
> refcount being more than 3 or 4 even in extreme cases.

That's an elegant idea; thanks.  I'll work this up and send a patch out for it.

Thanks,
Curt

>
> Cheers, Andreas
> --
> Andreas Dilger
> Sr. Staff Engineer, Lustre Group
> Sun Microsystems of Canada, Inc.
>
>
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Re: [PATCH 2/2] ext4: Handle nested ext4_journal_start/stop calls without a journal

[Curt Wohlgemuth]

Here's version 2, thanks to Andreas' suggestion.

Curt


This patch fixes a problem with handling nested calls to
ext4_journal_start/ext4_journal_stop, when there is no journal present.

	Signed-off-by: Curt Wohlgemuth <curtw@google.com>
---

Taking Andreas' suggestion, what I'm calling "an allocated handle that
doesn't use a journal" is now identified by a value in the range

   [1, 4095]

A handle with value 0 (NULL) still represents "an unallocated handle."

I added a comment atop ext4_handle_valid() to indicate that sending it a
NULL pointer was just wrong.

diff -uprN orig/fs/ext4/ext4_jbd2.h new/fs/ext4/ext4_jbd2.h
--- orig/fs/ext4/ext4_jbd2.h	2009-09-18 14:04:15.000000000 -0700
+++ new/fs/ext4/ext4_jbd2.h	2009-09-18 14:17:31.000000000 -0700
@@ -161,11 +161,13 @@ int __ext4_handle_dirty_metadata(const c
 handle_t *ext4_journal_start_sb(struct super_block *sb, int nblocks);
 int __ext4_journal_stop(const char *where, handle_t *handle);

-#define EXT4_NOJOURNAL_HANDLE	((handle_t *) 0x1)
+#define EXT4_NOJOURNAL_MAX_REF_COUNT ((unsigned long) 4096)

+/* Note:  Do not use this for NULL handles.  This is only to determine if
+ * a properly allocated handle is using a journal or not. */
 static inline int ext4_handle_valid(handle_t *handle)
 {
-	if (handle == EXT4_NOJOURNAL_HANDLE)
+	if ((unsigned long)handle < EXT4_NOJOURNAL_MAX_REF_COUNT)
 		return 0;
 	return 1;
 }
diff -uprN orig/fs/ext4/inode.c new/fs/ext4/inode.c
--- orig/fs/ext4/inode.c	2009-09-18 14:04:15.000000000 -0700
+++ new/fs/ext4/inode.c	2009-09-18 14:17:31.000000000 -0700
@@ -4931,12 +4931,14 @@ int ext4_write_inode(struct inode *inode
 		err = ext4_force_commit(inode->i_sb);
 	} else {
 		struct ext4_iloc iloc;
+		handle_t *handle = ext4_journal_start(inode, 1);

 		err = ext4_get_inode_loc(inode, &iloc);
 		if (err)
 			return err;
-		err = ext4_do_update_inode(EXT4_NOJOURNAL_HANDLE,
-					   inode, &iloc, wait);
+		err = ext4_do_update_inode(handle, inode, &iloc, wait);
+
+		ext4_journal_stop(handle);
 	}
 	return err;
 }
diff -uprN orig/fs/ext4/namei.c new/fs/ext4/namei.c
--- orig/fs/ext4/namei.c	2009-09-18 14:04:15.000000000 -0700
+++ new/fs/ext4/namei.c	2009-09-18 14:17:31.000000000 -0700
@@ -2076,7 +2076,8 @@ int ext4_orphan_del(handle_t *handle, st
 	struct ext4_iloc iloc;
 	int err = 0;

-	if (!ext4_handle_valid(handle))
+	/* ext4_handle_valid() assumes a valid handle_t pointer */
+	if (handle && !ext4_handle_valid(handle))
 		return 0;

 	mutex_lock(&EXT4_SB(inode->i_sb)->s_orphan_lock);
diff -uprN orig/fs/ext4/super.c new/fs/ext4/super.c
--- orig/fs/ext4/super.c	2009-09-18 14:04:15.000000000 -0700
+++ new/fs/ext4/super.c	2009-09-18 14:17:31.000000000 -0700
@@ -198,6 +198,36 @@ void ext4_itable_unused_set(struct super
 		bg->bg_itable_unused_hi = cpu_to_le16(count >> 16);
 }

+
+/* Just increment the non-pointer handle value */
+static handle_t *ext4_get_nojournal(void)
+{
+	handle_t *handle = current->journal_info;
+	unsigned long ref_cnt = (unsigned long)handle;
+
+	BUG_ON(ref_cnt >= EXT4_NOJOURNAL_MAX_REF_COUNT);
+
+	ref_cnt++;
+	handle = (handle_t *)ref_cnt;
+
+	current->journal_info = handle;
+	return handle;
+}
+
+
+/* Decrement the non-pointer handle value */
+static void ext4_put_nojournal(handle_t *handle)
+{
+	unsigned long ref_cnt = (unsigned long)handle;
+
+	BUG_ON(ref_cnt == 0);
+
+	ref_cnt--;
+	handle = (handle_t *)ref_cnt;
+
+	current->journal_info = handle;
+}
+
 /*
  * Wrappers for jbd2_journal_start/end.
  *
@@ -224,11 +254,7 @@ handle_t *ext4_journal_start_sb(struct s
 		}
 		return jbd2_journal_start(journal, nblocks);
 	}
-	/*
-	 * We're not journaling, return the appropriate indication.
-	 */
-	current->journal_info = EXT4_NOJOURNAL_HANDLE;
-	return current->journal_info;
+	return ext4_get_nojournal();
 }

 /*
@@ -244,11 +270,7 @@ int __ext4_journal_stop(const char *wher
 	int rc;

 	if (!ext4_handle_valid(handle)) {
-		/*
-		 * Do this here since we don't call jbd2_journal_stop() in
-		 * no-journal mode.
-		 */
-		current->journal_info = NULL;
+		ext4_put_nojournal(handle);
 		return 0;
 	}
 	sb = handle->h_transaction->t_journal->j_private;

Re: [PATCH 2/2] ext4: Handle nested ext4_journal_start/stop calls without a journal

[Curt Wohlgemuth]

Ted, do you have any comments or suggestions on this patch?
No-journal use of ext4 is definitely broken without it; we've seen
numerous crashes with the existing code, which doesn't ref count the
no-journal handle.

Thanks,
Curt


On Fri, Sep 18, 2009 at 2:33 PM, Curt Wohlgemuth <curtw@google.com> wrote:
> Here's version 2, thanks to Andreas' suggestion.
>
> Curt
>
>
> This patch fixes a problem with handling nested calls to
> ext4_journal_start/ext4_journal_stop, when there is no journal present.
>
>        Signed-off-by: Curt Wohlgemuth <curtw@google.com>
> ---
>
> Taking Andreas' suggestion, what I'm calling "an allocated handle that
> doesn't use a journal" is now identified by a value in the range
>
>   [1, 4095]
>
> A handle with value 0 (NULL) still represents "an unallocated handle."
>
> I added a comment atop ext4_handle_valid() to indicate that sending it a
> NULL pointer was just wrong.
>
> diff -uprN orig/fs/ext4/ext4_jbd2.h new/fs/ext4/ext4_jbd2.h
> --- orig/fs/ext4/ext4_jbd2.h    2009-09-18 14:04:15.000000000 -0700
> +++ new/fs/ext4/ext4_jbd2.h     2009-09-18 14:17:31.000000000 -0700
> @@ -161,11 +161,13 @@ int __ext4_handle_dirty_metadata(const c
>  handle_t *ext4_journal_start_sb(struct super_block *sb, int nblocks);
>  int __ext4_journal_stop(const char *where, handle_t *handle);
>
> -#define EXT4_NOJOURNAL_HANDLE  ((handle_t *) 0x1)
> +#define EXT4_NOJOURNAL_MAX_REF_COUNT ((unsigned long) 4096)
>
> +/* Note:  Do not use this for NULL handles.  This is only to determine if
> + * a properly allocated handle is using a journal or not. */
>  static inline int ext4_handle_valid(handle_t *handle)
>  {
> -       if (handle == EXT4_NOJOURNAL_HANDLE)
> +       if ((unsigned long)handle < EXT4_NOJOURNAL_MAX_REF_COUNT)
>                return 0;
>        return 1;
>  }
> diff -uprN orig/fs/ext4/inode.c new/fs/ext4/inode.c
> --- orig/fs/ext4/inode.c        2009-09-18 14:04:15.000000000 -0700
> +++ new/fs/ext4/inode.c 2009-09-18 14:17:31.000000000 -0700
> @@ -4931,12 +4931,14 @@ int ext4_write_inode(struct inode *inode
>                err = ext4_force_commit(inode->i_sb);
>        } else {
>                struct ext4_iloc iloc;
> +               handle_t *handle = ext4_journal_start(inode, 1);
>
>                err = ext4_get_inode_loc(inode, &iloc);
>                if (err)
>                        return err;
> -               err = ext4_do_update_inode(EXT4_NOJOURNAL_HANDLE,
> -                                          inode, &iloc, wait);
> +               err = ext4_do_update_inode(handle, inode, &iloc, wait);
> +
> +               ext4_journal_stop(handle);
>        }
>        return err;
>  }
> diff -uprN orig/fs/ext4/namei.c new/fs/ext4/namei.c
> --- orig/fs/ext4/namei.c        2009-09-18 14:04:15.000000000 -0700
> +++ new/fs/ext4/namei.c 2009-09-18 14:17:31.000000000 -0700
> @@ -2076,7 +2076,8 @@ int ext4_orphan_del(handle_t *handle, st
>        struct ext4_iloc iloc;
>        int err = 0;
>
> -       if (!ext4_handle_valid(handle))
> +       /* ext4_handle_valid() assumes a valid handle_t pointer */
> +       if (handle && !ext4_handle_valid(handle))
>                return 0;
>
>        mutex_lock(&EXT4_SB(inode->i_sb)->s_orphan_lock);
> diff -uprN orig/fs/ext4/super.c new/fs/ext4/super.c
> --- orig/fs/ext4/super.c        2009-09-18 14:04:15.000000000 -0700
> +++ new/fs/ext4/super.c 2009-09-18 14:17:31.000000000 -0700
> @@ -198,6 +198,36 @@ void ext4_itable_unused_set(struct super
>                bg->bg_itable_unused_hi = cpu_to_le16(count >> 16);
>  }
>
> +
> +/* Just increment the non-pointer handle value */
> +static handle_t *ext4_get_nojournal(void)
> +{
> +       handle_t *handle = current->journal_info;
> +       unsigned long ref_cnt = (unsigned long)handle;
> +
> +       BUG_ON(ref_cnt >= EXT4_NOJOURNAL_MAX_REF_COUNT);
> +
> +       ref_cnt++;
> +       handle = (handle_t *)ref_cnt;
> +
> +       current->journal_info = handle;
> +       return handle;
> +}
> +
> +
> +/* Decrement the non-pointer handle value */
> +static void ext4_put_nojournal(handle_t *handle)
> +{
> +       unsigned long ref_cnt = (unsigned long)handle;
> +
> +       BUG_ON(ref_cnt == 0);
> +
> +       ref_cnt--;
> +       handle = (handle_t *)ref_cnt;
> +
> +       current->journal_info = handle;
> +}
> +
>  /*
>  * Wrappers for jbd2_journal_start/end.
>  *
> @@ -224,11 +254,7 @@ handle_t *ext4_journal_start_sb(struct s
>                }
>                return jbd2_journal_start(journal, nblocks);
>        }
> -       /*
> -        * We're not journaling, return the appropriate indication.
> -        */
> -       current->journal_info = EXT4_NOJOURNAL_HANDLE;
> -       return current->journal_info;
> +       return ext4_get_nojournal();
>  }
>
>  /*
> @@ -244,11 +270,7 @@ int __ext4_journal_stop(const char *wher
>        int rc;
>
>        if (!ext4_handle_valid(handle)) {
> -               /*
> -                * Do this here since we don't call jbd2_journal_stop() in
> -                * no-journal mode.
> -                */
> -               current->journal_info = NULL;
> +               ext4_put_nojournal(handle);
>                return 0;
>        }
>        sb = handle->h_transaction->t_journal->j_private;
>
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