linux-kernel - [PATCH] ocfs2: fix check if list iterator did find an element

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Date:   Sat, 19 Mar 2022 21:31:06 +0100
From:   Jakob Koschel <jakobkoschel@...il.com>
To:     Mark Fasheh <mark@...heh.com>
Cc:     Jakob Koschel <jakobkoschel@...il.com>,
        linux-kernel@...r.kernel.org, ocfs2-devel@....oracle.com,
        Joel Becker <jlbec@...lplan.org>,
        Joseph Qi <joseph.qi@...ux.alibaba.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Miguel Ojeda <ojeda@...nel.org>,
        Mike Rapoport <rppt@...nel.org>,
        "Brian Johannesmeyer" <bjohannesmeyer@...il.com>,
        Cristiano Giuffrida <c.giuffrida@...nl>,
        "Bos, H.J." <h.j.bos@...nl>
Subject: [PATCH] ocfs2: fix check if list iterator did find an element

Instead of setting 'res' to NULL, it should only be set if
the suitable element was found.

In the original code 'res' would have been set to an incorrect pointer
if the list is empty.

In preparation to limit the scope of the list iterator to the list
traversal loop, use a dedicated pointer pointing to the found element [1].

Link: https://lore.kernel.org/all/YhdfEIwI4EdtHdym@kroah.com/
Signed-off-by: Jakob Koschel <jakobkoschel@...il.com>
---
 fs/ocfs2/dlm/dlmdebug.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/fs/ocfs2/dlm/dlmdebug.c b/fs/ocfs2/dlm/dlmdebug.c
index d442cf5dda8a..be5e9ed7da8d 100644
--- a/fs/ocfs2/dlm/dlmdebug.c
+++ b/fs/ocfs2/dlm/dlmdebug.c
@@ -541,7 +541,7 @@ static void *lockres_seq_start(struct seq_file *m, loff_t *pos)
 	struct debug_lockres *dl = m->private;
 	struct dlm_ctxt *dlm = dl->dl_ctxt;
 	struct dlm_lock_resource *oldres = dl->dl_res;
-	struct dlm_lock_resource *res = NULL;
+	struct dlm_lock_resource *res = NULL, *iter;
 	struct list_head *track_list;

 	spin_lock(&dlm->track_lock);
@@ -556,11 +556,11 @@ static void *lockres_seq_start(struct seq_file *m, loff_t *pos)
 		}
 	}

-	list_for_each_entry(res, track_list, tracking) {
-		if (&res->tracking == &dlm->tracking_list)
-			res = NULL;
-		else
-			dlm_lockres_get(res);
+	list_for_each_entry(iter, track_list, tracking) {
+		if (&iter->tracking != &dlm->tracking_list) {
+			dlm_lockres_get(iter);
+			res = iter;
+		}
 		break;
 	}
 	spin_unlock(&dlm->track_lock);

base-commit: 34e047aa16c0123bbae8e2f6df33e5ecc1f56601
--
2.25.1