xfs
[Top] [All Lists]

Re: [PATCH 2/4] vfs: Protect write paths by sb_start_write - sb_end_writ

To: Jan Kara <jack@xxxxxxx>
Subject: Re: [PATCH 2/4] vfs: Protect write paths by sb_start_write - sb_end_write
From: Andreas Dilger <adilger@xxxxxxxxx>
Date: Thu, 12 Jan 2012 12:56:01 -0700
Cc: linux-fsdevel@xxxxxxxxxxxxxxx, LKML <linux-kernel@xxxxxxxxxxxxxxx>, linux-ext4@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, Eric Sandeen <sandeen@xxxxxxxxxxx>, Dave Chinner <dchinner@xxxxxxxxxx>, Surbhi Palande <csurbhi@xxxxxxxxx>, Kamal Mostafa <kamal@xxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>
In-reply-to: <1326331253-6497-3-git-send-email-jack@xxxxxxx>
References: <1326331253-6497-1-git-send-email-jack@xxxxxxx> <1326331253-6497-3-git-send-email-jack@xxxxxxx>
On 2012-01-11, at 6:20 PM, Jan Kara wrote:
> There are three entry points which dirty pages in a filesystem.  mmap (handled
> by block_page_mkwrite()), buffered write (handled by
> __generic_file_aio_write()), and truncate (it can dirty last partial page -
> handled by do_truncate()). Protect these places with sb_start_write() and
> sb_end_write().
> 
> Signed-off-by: Jan Kara <jack@xxxxxxx>
> ---
> fs/buffer.c  |   18 ++----------------
> fs/open.c    |    6 ++++++
> mm/filemap.c |    3 ++-
> 3 files changed, 10 insertions(+), 17 deletions(-)
> 
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 19d8eb7..8519405 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -2371,18 +2371,7 @@ int __block_page_mkwrite(struct vm_area_struct *vma, 
> struct vm_fault *vmf,

The comment for __block_page_mkwrite() needs to be updated to reference
sb_start_write() and sb_end_write() instead of vfs_check_frozen().

Cheers, Andreas

>       if (unlikely(ret < 0))
>               goto out_unlock;
> -     /*
> -      * Freezing in progress? We check after the page is marked dirty and
> -      * with page lock held so if the test here fails, we are sure freezing
> -      * code will wait during syncing until the page fault is done - at that
> -      * point page will be dirty and unlocked so freezing code will write it
> -      * and writeprotect it again.
> -      */
>       set_page_dirty(page);
> -     if (inode->i_sb->s_frozen != SB_UNFROZEN) {
> -             ret = -EAGAIN;
> -             goto out_unlock;
> -     }
>       wait_on_page_writeback(page);
>       return 0;
> out_unlock:
> @@ -2397,12 +2386,9 @@ int block_page_mkwrite(struct vm_area_struct *vma, 
> struct vm_fault *vmf,
>       int ret;
>       struct super_block *sb = vma->vm_file->f_path.dentry->d_inode->i_sb;
> 
> -     /*
> -      * This check is racy but catches the common case. The check in
> -      * __block_page_mkwrite() is reliable.
> -      */
> -     vfs_check_frozen(sb, SB_FREEZE_WRITE);
> +     sb_start_write(sb);
>       ret = __block_page_mkwrite(vma, vmf, get_block);
> +     sb_end_write(sb);
>       return block_page_mkwrite_return(ret);
> }
> EXPORT_SYMBOL(block_page_mkwrite);
> diff --git a/fs/open.c b/fs/open.c
> index 22c41b5..ee17c90 100644
> --- a/fs/open.c
> +++ b/fs/open.c
> @@ -55,8 +55,14 @@ int do_truncate(struct dentry *dentry, loff_t length, 
> unsigned int time_attrs,
>       if (ret)
>               newattrs.ia_valid |= ret | ATTR_FORCE;
> 
> +     /*
> +      * Truncate can dirty last partial page so we need protection against
> +      * filesystem freezing.
> +      */
>       mutex_lock(&dentry->d_inode->i_mutex);
> +     sb_start_write(dentry->d_sb);
>       ret = notify_change(dentry, &newattrs);
> +     sb_end_write(dentry->d_sb);
>       mutex_unlock(&dentry->d_inode->i_mutex);
>       return ret;
> }
> diff --git a/mm/filemap.c b/mm/filemap.c
> index c0018f2..6566c73 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -2529,7 +2529,7 @@ ssize_t __generic_file_aio_write(struct kiocb *iocb, 
> const struct iovec *iov,
>       count = ocount;
>       pos = *ppos;
> 
> -     vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
> +     sb_start_write(inode->i_sb);
> 
>       /* We can write back this queue in page reclaim */
>       current->backing_dev_info = mapping->backing_dev_info;
> @@ -2601,6 +2601,7 @@ ssize_t __generic_file_aio_write(struct kiocb *iocb, 
> const struct iovec *iov,
>                               pos, ppos, count, written);
>       }
> out:
> +     sb_end_write(inode->i_sb);
>       current->backing_dev_info = NULL;
>       return written ? written : err;
> }
> -- 
> 1.7.1
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at  http://vger.kernel.org/majordomo-info.html


<Prev in Thread] Current Thread [Next in Thread>