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From:   Vasily Averin <vvs@virtuozzo.com>
Subject: [PATCH 1/1] jbd2_seq_info_next should increase position index
To:     linux-ext4@vger.kernel.org, Theodore Ts'o <tytso@mit.edu>
Cc:     Jan Kara <jack@suse.com>
Message-ID: <d13805e5-695e-8ac3-b678-26ca2313629f@virtuozzo.com>
Date:   Thu, 23 Jan 2020 12:05:10 +0300
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if seq_file .next fuction does not change position index,
read after some lseek can generate unexpected output.

Script below generates endless output
 $ q=;while read -r r;do echo "$((++q)) $r";done </proc/fs/jbd2/DEV/info

https://bugzilla.kernel.org/show_bug.cgi?id=206283
Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
---
 fs/jbd2/journal.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 5e408ee..b3e2433 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -982,6 +982,7 @@ static void *jbd2_seq_info_start(struct seq_file *seq, loff_t *pos)
 
 static void *jbd2_seq_info_next(struct seq_file *seq, void *v, loff_t *pos)
 {
+	(*pos)++;
 	return NULL;
 }
 
-- 
1.8.3.1