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cgroup-v1: cgroup_pidlist_next should update position index 

[ Upstream commit db8dd96972 ]

if seq_file .next fuction does not change position index,
read after some lseek can generate unexpected output.

 # mount | grep cgroup
 # dd if=/mnt/cgroup.procs bs=1  # normal output
...
1294
1295
1296
1304
1382
584+0 records in
584+0 records out
584 bytes copied

dd: /mnt/cgroup.procs: cannot skip to specified offset
83  <<< generates end of last line
1383  <<< ... and whole last line once again
0+1 records in
0+1 records out
8 bytes copied

dd: /mnt/cgroup.procs: cannot skip to specified offset
1386  <<< generates last line anyway
0+1 records in
0+1 records out
5 bytes copied

https://bugzilla.kernel.org/show_bug.cgi?id=206283
Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
5.4-rM2-2.2.x-imx-squashed
Vasily Averin 2020-01-30 13:34:49 +03:00 committed by Greg Kroah-Hartman
parent 74f554af84
commit b51274fabe
1 changed files with 1 additions and 0 deletions
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kernel/cgroup/cgroup-v1.c
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@ -473,6 +473,7 @@ static void *cgroup_pidlist_next(struct seq_file *s, void *v, loff_t *pos)
*/
p++;
if (p >= end) {
(*pos)++;
return NULL;
} else {
*pos = *p;