From: Dave Chinner <dchinner@xxxxxxxxxx>
lockdep reports splice vs direct-io write lock inversions due to
generic_file_splice_write() taking the inode->i_mutex inside
XFS_IOLOCK_EXCL context. These lock contexts are inverted, hence can
deadlock. Remove the XFS_IOLOCK_EXCL locking context from the outer
function and drive it inwards to the actor function that only locks
the inode when the lock is really needed,
Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
---
fs/xfs/xfs_file.c | 40 +++++++++++++++++++++++++++++-----------
1 file changed, 29 insertions(+), 11 deletions(-)
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 2e79c54..21b6f0b 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -39,6 +39,7 @@
#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;
@@ -344,13 +345,33 @@ xfs_file_splice_read(
return ret;
}
+static ssize_t
+xfs_file_splice_write_actor(
+ struct pipe_inode_info *pipe,
+ struct splice_desc *sd)
+{
+ struct file *out = sd->u.file;
+ struct xfs_inode *ip = XFS_I(out->f_mapping->host);
+ ssize_t ret;
+
+ xfs_rw_ilock(ip, XFS_IOLOCK_EXCL);
+ ret = file_remove_suid(out);
+ if (!ret) {
+ ret = file_update_time(out);
+ if (!ret)
+ ret = splice_from_pipe_feed(pipe, sd, pipe_to_file);
+ }
+ xfs_rw_iunlock(ip, XFS_IOLOCK_EXCL);
+
+ 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.
+ * xfs_file_splice_write() does not use the generic file splice write path
+ * because that takes the i_mutex, causing lock inversions with the IOLOCK.
+ * Instead, we call splice_write_to_file() directly with our own actor that does
+ * not take the i_mutex. This allows us to use the xfs_rw_ilock() functions like
+ * the rest of the code and hence avoid lock inversions and deadlocks.
*/
STATIC ssize_t
xfs_file_splice_write(
@@ -373,15 +394,12 @@ xfs_file_splice_write(
if (XFS_FORCED_SHUTDOWN(ip->i_mount))
return -EIO;
- xfs_ilock(ip, XFS_IOLOCK_EXCL);
-
trace_xfs_file_splice_write(ip, count, *ppos, ioflags);
- ret = generic_file_splice_write(pipe, outfilp, ppos, count, flags);
+ ret = splice_write_to_file(pipe, outfilp, ppos, count, flags,
+ xfs_file_splice_write_actor);
if (ret > 0)
XFS_STATS_ADD(xs_write_bytes, ret);
-
- xfs_iunlock(ip, XFS_IOLOCK_EXCL);
return ret;
}
--
1.7.10
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