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From:   Vasily Averin <vvs@virtuozzo.com>
Subject: [PATCH] seq_read: info message about buggy .next functions
To:     linux-kernel@vger.kernel.org
Cc:     NeilBrown <neilb@suse.com>
References: <244674e5-760c-86bd-d08a-047042881748@virtuozzo.com>
Message-ID: <7c24087c-e280-e580-5b0c-0cdaeb14cd18@virtuozzo.com>
Date:   Fri, 24 Jan 2020 10:47:13 +0300
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It helps to detect missed or out-of-tree incorect .next seq_file functions

https://bugzilla.kernel.org/show_bug.cgi?id=206283
Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
---
 fs/seq_file.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/seq_file.c b/fs/seq_file.c
index 1600034..07c6909 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -256,9 +256,12 @@ ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
 		loff_t pos = m->index;
 
 		p = m->op->next(m, p, &m->index);
-		if (pos == m->index)
-			/* Buggy ->next function */
+		if (pos == m->index) {
+			pr_info("buggy seq_file .next function %ps "
+				"did not updated position index\n",
+				m->op->next);
 			m->index++;
+		}
 		if (!p || IS_ERR(p)) {
 			err = PTR_ERR(p);
 			break;
-- 
1.8.3.1