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Date: Wed, 23 Sep 2009 07:39:43 -0700
From: Curt Wohlgemuth <curtw@...gle.com>
To: ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 2/2] ext4: Handle nested ext4_journal_start/stop calls
without a journal
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@...gle.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@...gle.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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