linux-kernel - [PATCH 2/2] ceph: pagecache writeback fault injection switch

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Date:   Tue, 25 Jul 2017 10:50:42 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     "Yan, Zheng" <zyan@...hat.com>, Sage Weil <sage@...hat.com>,
        Ilya Dryomov <idryomov@...il.com>
Cc:     ceph-devel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] ceph: pagecache writeback fault injection switch

From: Jeff Layton <jlayton@...hat.com>

Testing ceph for proper writeback error handling turns out to be quite
difficult. I tried using iptables to block traffic but that didn't
give reliable results.

I hacked in this wb_fault switch that makes the filesystem pretend that
writeback failed, even when it succeeds. With this, I could verify that
cephfs fsync error reporting does work properly.

Signed-off-by: Jeff Layton <jlayton@...hat.com>
---
 fs/ceph/addr.c    | 7 +++++++
 fs/ceph/debugfs.c | 8 +++++++-
 fs/ceph/super.h   | 2 ++
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
index 50836280a6f8..a3831d100e16 100644
--- a/fs/ceph/addr.c
+++ b/fs/ceph/addr.c
@@ -584,6 +584,10 @@ static int writepage_nounlock(struct page *page, struct writeback_control *wbc)
 				   page_off, len,
 				   truncate_seq, truncate_size,
 				   &inode->i_mtime, &page, 1);
+
+	if (fsc->wb_fault && err >= 0)
+		err = -EIO;
+
 	if (err < 0) {
 		struct writeback_control tmp_wbc;
 		if (!wbc)
@@ -666,6 +670,9 @@ static void writepages_finish(struct ceph_osd_request *req)
 	struct ceph_fs_client *fsc = ceph_inode_to_client(inode);
 	bool remove_page;
 
+	if (fsc->wb_fault && rc >= 0)
+		rc = -EIO;
+
 	dout("writepages_finish %p rc %d\n", inode, rc);
 	if (rc < 0) {
 		mapping_set_error(mapping, rc);
diff --git a/fs/ceph/debugfs.c b/fs/ceph/debugfs.c
index 4e2d112c982f..e1e6eaa12031 100644
--- a/fs/ceph/debugfs.c
+++ b/fs/ceph/debugfs.c
@@ -197,7 +197,6 @@ CEPH_DEFINE_SHOW_FUNC(caps_show)
 CEPH_DEFINE_SHOW_FUNC(dentry_lru_show)
 CEPH_DEFINE_SHOW_FUNC(mds_sessions_show)
 
-
 /*
  * debugfs
  */
@@ -231,6 +230,7 @@ void ceph_fs_debugfs_cleanup(struct ceph_fs_client *fsc)
 	debugfs_remove(fsc->debugfs_caps);
 	debugfs_remove(fsc->debugfs_mdsc);
 	debugfs_remove(fsc->debugfs_dentry_lru);
+	debugfs_remove(fsc->debugfs_wb_fault);
 }
 
 int ceph_fs_debugfs_init(struct ceph_fs_client *fsc)
@@ -298,6 +298,12 @@ int ceph_fs_debugfs_init(struct ceph_fs_client *fsc)
 	if (!fsc->debugfs_dentry_lru)
 		goto out;
 
+	fsc->debugfs_wb_fault = debugfs_create_bool("wb_fault",
+					0600, fsc->client->debugfs_dir,
+					&fsc->wb_fault);
+	if (!fsc->debugfs_wb_fault)
+		goto out;
+
 	return 0;
 
 out:
diff --git a/fs/ceph/super.h b/fs/ceph/super.h
index f02a2225fe42..a38fd6203b77 100644
--- a/fs/ceph/super.h
+++ b/fs/ceph/super.h
@@ -84,6 +84,7 @@ struct ceph_fs_client {
 
 	unsigned long mount_state;
 	int min_caps;                  /* min caps i added */
+	bool wb_fault;
 
 	struct ceph_mds_client *mdsc;
 
@@ -100,6 +101,7 @@ struct ceph_fs_client {
 	struct dentry *debugfs_bdi;
 	struct dentry *debugfs_mdsc, *debugfs_mdsmap;
 	struct dentry *debugfs_mds_sessions;
+	struct dentry *debugfs_wb_fault;
 #endif
 
 #ifdef CONFIG_CEPH_FSCACHE
-- 
2.13.3