Re: [PATCH 1/2] vfs: split generic splice code from i_mutex locking

Jan Kara
2011-08-09T11:36:46Z

On Mon 08-08-11 16:45:26, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> XFS holds locks that should be nested inside the inode->i_mutex when
> generic_file_splice_write is called. This function takes the
> i_mutex, and so we get a lock inversion that triggers lockdep
> warnings and has been found to cause real deadlocks.
>
> XFS does not need the splice code to take the i_mutex to do the page
> cache manipulation, so modify the generic splice code to use an
> actor function for the code that currently requires the i_mutex to
> be taken. Convert generic_file_splice_write() to use this new
> interface supplying a generic actor function that performs the same
> actions as the existing code.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
The patch looks good to me.
Reviewed-by: Jan Kara <jack@suse.cz>

Honza
> ---
> fs/splice.c | 58 ++++++++++++++++++++++++++++++++++++++----------
> include/linux/splice.h | 5 ++++
> 2 files changed, 51 insertions(+), 12 deletions(-)
>
> diff --git a/fs/splice.c b/fs/splice.c
> index fa2defa..a02dddc 100644
> --- a/fs/splice.c
> +++ b/fs/splice.c
> @@ -967,24 +967,24 @@ ssize_t splice_from_pipe(struct pipe_inode_info *pipe, struct file *out,
> }
>
> /**
> - * generic_file_splice_write - splice data from a pipe to a file
> + * splice_write_to_file - splice data from a pipe to a file
> * @pipe: pipe info
> * @out: file to write to
> * @ppos: position in @out
> * @len: number of bytes to splice
> * @flags: splice modifier flags
> + * @actor: worker that does the splicing from the pipe to the file
> *
> * Description:
> * Will either move or copy pages (determined by @flags options) from
> * the given pipe inode to the given file.
> *
> */
> -ssize_t
> -generic_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
> - loff_t *ppos, size_t len, unsigned int flags)
> +ssize_t splice_write_to_file(struct pipe_inode_info *pipe, struct file *out,
> + loff_t *ppos, size_t len, unsigned int flags,
> + splice_write_actor actor)
> {
> struct address_space *mapping = out->f_mapping;
> - struct inode *inode = mapping->host;
> struct splice_desc sd = {
> .total_len = len,
> .flags = flags,
> @@ -1001,13 +1001,8 @@ generic_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
> if (ret <= 0)
> break;
>
> - mutex_lock_nested(&inode->i_mutex, I_MUTEX_CHILD);
> - ret = file_remove_suid(out);
> - if (!ret) {
> - file_update_time(out);
> - ret = splice_from_pipe_feed(pipe, &sd, pipe_to_file);
> - }
> - mutex_unlock(&inode->i_mutex);
> + ret = actor(pipe, &sd);
> +
> } while (ret > 0);
> splice_from_pipe_end(pipe, &sd);
>
> @@ -1032,7 +1027,46 @@ generic_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
>
> return ret;
> }
> +EXPORT_SYMBOL(splice_write_to_file);
>
> +static ssize_t generic_file_splice_write_actor(struct pipe_inode_info *pipe,
> + struct splice_desc *sd)
> +{
> + struct file *out = sd->u.file;
> + struct inode *inode = out->f_mapping->host;
> + ssize_t ret;
> +
> + mutex_lock_nested(&inode->i_mutex, I_MUTEX_CHILD);
> + ret = file_remove_suid(out);
> + if (!ret) {
> + file_update_time(out);
> + ret = splice_from_pipe_feed(pipe, sd, pipe_to_file);
> + }
> + mutex_unlock(&inode->i_mutex);
> +
> + return ret;
> +}
> +
> +/**
> + * generic_file_splice_write - splice data from a pipe to a file
> + * @pipe: pipe info
> + * @out: file to write to
> + * @ppos: position in @out
> + * @len: number of bytes to splice
> + * @flags: splice modifier flags
> + *
> + * Description:
> + * Will either move or copy pages (determined by @flags options) from
> + * the given pipe inode to the given file.
> + *
> + */
> +ssize_t
> +generic_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
> + loff_t *ppos, size_t len, unsigned int flags)
> +{
> + return splice_write_to_file(pipe, out, ppos, len, flags,
> + generic_file_splice_write_actor);
> +}
> EXPORT_SYMBOL(generic_file_splice_write);
>
> static int write_pipe_buf(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
> diff --git a/include/linux/splice.h b/include/linux/splice.h
> index 26e5b61..bd14281 100644
> --- a/include/linux/splice.h
> +++ b/include/linux/splice.h
> @@ -61,6 +61,8 @@ typedef int (splice_actor)(struct pipe_inode_info *, struct pipe_buffer *,
> struct splice_desc *);
> typedef int (splice_direct_actor)(struct pipe_inode_info *,
> struct splice_desc *);
> +typedef ssize_t (splice_write_actor)(struct pipe_inode_info *,
> + struct splice_desc *);
>
> extern ssize_t splice_from_pipe(struct pipe_inode_info *, struct file *,
> loff_t *, size_t, unsigned int,
> @@ -82,6 +84,9 @@ extern ssize_t splice_to_pipe(struct pipe_inode_info *,
> extern ssize_t splice_direct_to_actor(struct file *, struct splice_desc *,
> splice_direct_actor *);
>
> +extern ssize_t splice_write_to_file(struct pipe_inode_info *, struct file *,
> + loff_t *, size_t, unsigned int,
> + splice_write_actor *);
> /*
> * for dynamic pipe sizing
> */
> --
> 1.7.5.4
>
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--
Jan Kara <jack@suse.cz>
SUSE Labs, CR