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[PATCH 4/5] xfs: fix splice_write locking

To: Al Viro <viro@xxxxxxxxxxxxxxxxxx>, Jens Axboe <axboe@xxxxxxxxx>, Mark Fasheh <mfasheh@xxxxxxxx>, Joel Becker <jlbec@xxxxxxxxxxxx>
Subject: [PATCH 4/5] xfs: fix splice_write locking
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Thu, 12 Dec 2013 10:15:03 -0800
Cc: linux-fsdevel@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
References: <20131212181459.994196463@xxxxxxxxxxxxxxxxxxxxxx>
User-agent: quilt/0.60-1
Call splice_from_pipe directly from XFS so that we can do our normal
I/O path locking.  This fixes a rare to hit deadlock vs direct I/O
as reported by Dave Chinner long time ago.

Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
 fs/xfs/xfs_file.c |   26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 52c91e1..9d0da98 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -43,6 +43,7 @@
 #include <linux/dcache.h>
 #include <linux/falloc.h>
 #include <linux/pagevec.h>
+#include <linux/splice.h>
 
 static const struct vm_operations_struct xfs_file_vm_ops;
 
@@ -348,14 +349,6 @@ xfs_file_splice_read(
        return ret;
 }
 
-/*
- * xfs_file_splice_write() does not use xfs_rw_ilock() because
- * generic_file_splice_write() takes the i_mutex itself. This, in theory,
- * couuld cause lock inversions between the aio_write path and the splice path
- * if someone is doing concurrent splice(2) based writes and write(2) based
- * writes to the same inode. The only real way to fix this is to re-implement
- * the generic code here with correct locking orders.
- */
 STATIC ssize_t
 xfs_file_splice_write(
        struct pipe_inode_info  *pipe,
@@ -377,15 +370,22 @@ xfs_file_splice_write(
        if (XFS_FORCED_SHUTDOWN(ip->i_mount))
                return -EIO;
 
-       xfs_ilock(ip, XFS_IOLOCK_EXCL);
-
+       xfs_rw_ilock(ip, XFS_IOLOCK_EXCL);
        trace_xfs_file_splice_write(ip, count, *ppos, ioflags);
+       ret = splice_from_pipe(pipe, outfilp, ppos, count, flags, pipe_to_file);
+       xfs_rw_iunlock(ip, XFS_IOLOCK_EXCL);
+
+       if (ret > 0) {
+               int err;
 
-       ret = generic_file_splice_write(pipe, outfilp, ppos, count, flags);
-       if (ret > 0)
                XFS_STATS_ADD(xs_write_bytes, ret);
 
-       xfs_iunlock(ip, XFS_IOLOCK_EXCL);
+               err = generic_write_sync(outfilp, *ppos, ret);
+               if (err)
+                       return err;
+               *ppos += ret;
+       }
+
        return ret;
 }
 
-- 
1.7.10.4


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