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[RFC PATCH 2/6] xfs: use i_mmaplock on read faults

To: xfs@xxxxxxxxxxx
Subject: [RFC PATCH 2/6] xfs: use i_mmaplock on read faults
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Thu, 8 Jan 2015 09:25:39 +1100
Cc: linux-fsdevel@xxxxxxxxxxxxxxx, linux-mm@xxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1420669543-8093-1-git-send-email-david@xxxxxxxxxxxxx>
References: <1420669543-8093-1-git-send-email-david@xxxxxxxxxxxxx>
From: Dave Chinner <dchinner@xxxxxxxxxx>

Take the i_mmaplock over read page faults. These come through the
->fault callout, so we need to wrap the generic implementation
with the i_mmaplock. While there, add tracepoints for the read
fault as it passes through XFS.

This gives us a lock order of mmap_sem -> i_mmaplock -> page_lock
-> i_lock.

Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
---
 fs/xfs/xfs_file.c  | 28 +++++++++++++++++++++++++++-
 fs/xfs/xfs_trace.h |  2 ++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 13e974e..87535e6 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -1349,6 +1349,32 @@ xfs_file_llseek(
        }
 }
 
+/*
+ * Locking for serialisation of IO during page faults. This results in a lock
+ * ordering of:
+ *
+ * mmap_sem (MM)
+ *   i_mmap_lock (XFS - truncate serialisation)
+ *     page_lock (MM)
+ *       i_lock (XFS - extent map serialisation)
+ */
+STATIC int
+xfs_filemap_fault(
+       struct vm_area_struct   *vma,
+       struct vm_fault         *vmf)
+{
+       struct xfs_inode        *ip = XFS_I(vma->vm_file->f_mapping->host);
+       int                     error;
+
+       trace_xfs_filemap_fault(ip);
+
+       xfs_ilock(ip, XFS_MMAPLOCK_SHARED);
+       error = filemap_fault(vma, vmf);
+       xfs_iunlock(ip, XFS_MMAPLOCK_SHARED);
+
+       return error;
+}
+
 const struct file_operations xfs_file_operations = {
        .llseek         = xfs_file_llseek,
        .read           = new_sync_read,
@@ -1381,7 +1407,7 @@ const struct file_operations xfs_dir_file_operations = {
 };
 
 static const struct vm_operations_struct xfs_file_vm_ops = {
-       .fault          = filemap_fault,
+       .fault          = xfs_filemap_fault,
        .map_pages      = filemap_map_pages,
        .page_mkwrite   = xfs_vm_page_mkwrite,
        .remap_pages    = generic_file_remap_pages,
diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
index 51372e3..c496153 100644
--- a/fs/xfs/xfs_trace.h
+++ b/fs/xfs/xfs_trace.h
@@ -685,6 +685,8 @@ DEFINE_INODE_EVENT(xfs_inode_set_eofblocks_tag);
 DEFINE_INODE_EVENT(xfs_inode_clear_eofblocks_tag);
 DEFINE_INODE_EVENT(xfs_inode_free_eofblocks_invalid);
 
+DEFINE_INODE_EVENT(xfs_filemap_fault);
+
 DECLARE_EVENT_CLASS(xfs_iref_class,
        TP_PROTO(struct xfs_inode *ip, unsigned long caller_ip),
        TP_ARGS(ip, caller_ip),
-- 
2.0.0

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