[PATCH 5.11 053/601] md: Fix missing unused status line of /proc/mdstat

Greg Kroah-Hartman
2021-05-12T16:53:24Z

From: Jan Glauber <jglauber@digitalocean.com>

commit 7abfabaf5f805f5171d133ce6af9b65ab766e76a upstream.

Reading /proc/mdstat with a read buffer size that would not
fit the unused status line in the first read will skip this
line from the output.

So 'dd if=/proc/mdstat bs=64 2>/dev/null' will not print something
like: unused devices: <none>

Don't return NULL immediately in start() for v=2 but call
show() once to print the status line also for multiple reads.

Cc: stable@vger.kernel.org
Fixes: 1f4aace60b0e ("fs/seq_file.c: simplify seq_file iteration code and interface")
Signed-off-by: Jan Glauber <jglauber@digitalocean.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/md/md.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -8187,7 +8187,11 @@ static void *md_seq_start(struct seq_fil
loff_t l = *pos;
struct mddev *mddev;

- if (l >= 0x10000)
+ if (l == 0x10000) {
+ ++*pos;
+ return (void *)2;
+ }
+ if (l > 0x10000)
return NULL;
if (!l--)
/* header */