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

Dave Chinner
2011-08-08T06:45:47Z

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>
---
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