[PATCH AUTOSEL 4.9 17/17] ocfs2: ocfs2_downconvert_lock failure results in deadlock

[Sasha Levin]

From: Gang He <ghe@xxxxxxxx>

[ Upstream commit 9673e0050c39b0534d0e2ca431223f52089f4959 ]

Usually, ocfs2_downconvert_lock() function always downconverts dlm lock to
the expected level for satisfy dlm bast requests from the other nodes.

But there is a rare situation.  When dlm lock conversion is being
canceled, ocfs2_downconvert_lock() function will return -EBUSY.  You need
to be aware that ocfs2_cancel_convert() function is asynchronous in fsdlm
implementation.

If we does not requeue this lockres entry, ocfs2 downconvert thread no
longer handles this dlm lock bast request.  Then, the other nodes will not
get the dlm lock again, the current node's process will be blocked when
acquire this dlm lock again.

Link: https://lkml.kernel.org/r/20210830044621.12544-1-ghe@xxxxxxxx
Signed-off-by: Gang He <ghe@xxxxxxxx>
Reviewed-by: Joseph Qi <joseph.qi@xxxxxxxxxxxxxxxxx>
Cc: Mark Fasheh <mark@xxxxxxxxxx>
Cc: Joel Becker <jlbec@xxxxxxxxxxxx>
Cc: Junxiao Bi <junxiao.bi@xxxxxxxxxx>
Cc: Changwei Ge <gechangwei@xxxxxxx>
Cc: Gang He <ghe@xxxxxxxx>
Cc: Jun Piao <piaojun@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 fs/ocfs2/dlmglue.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
index 2c3e975126b3..2e6aee19e536 100644
--- a/fs/ocfs2/dlmglue.c
+++ b/fs/ocfs2/dlmglue.c
@@ -32,6 +32,7 @@
 #include <linux/debugfs.h>
 #include <linux/seq_file.h>
 #include <linux/time.h>
+#include <linux/delay.h>
 #include <linux/quotaops.h>
 
 #define MLOG_MASK_PREFIX ML_DLM_GLUE
@@ -3677,6 +3678,17 @@ static int ocfs2_unblock_lock(struct ocfs2_super *osb,
 	spin_unlock_irqrestore(&lockres->l_lock, flags);
 	ret = ocfs2_downconvert_lock(osb, lockres, new_level, set_lvb,
 				     gen);
+	/* The dlm lock convert is being cancelled in background,
+	 * ocfs2_cancel_convert() is asynchronous in fs/dlm,
+	 * requeue it, try again later.
+	 */
+	if (ret == -EBUSY) {
+		ctl->requeue = 1;
+		mlog(ML_BASTS, "lockres %s, ReQ: Downconvert busy\n",
+		     lockres->l_name);
+		ret = 0;
+		msleep(20);
+	}
 
 leave:
 	if (ret)
-- 
2.30.2