blkcg: update blkcg_print_stat() to handle larger outputs
Depending on the number of devices, blkcg stats can go over the
default seqfile buf size. seqfile normally retries with a larger
buffer but since the ->pd_stat() addition, blkcg_print_stat() doesn't
tell seqfile that overflow has happened and the output gets printed
truncated. Fix it by calling seq_commit() w/ -1 on possible
overflows.
Signed-off-by: Tejun Heo <tj@kernel.org>
Fixes: 903d23f0a354 ("blk-cgroup: allow controllers to output their own stats")
Cc: stable@vger.kernel.org # v4.19+
Cc: Josef Bacik <jbacik@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 1f7127b..e4715b3 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1006,8 +1006,12 @@ static int blkcg_print_stat(struct seq_file *sf, void *v)
}
next:
if (has_stats) {
- off += scnprintf(buf+off, size-off, "\n");
- seq_commit(sf, off);
+ if (off < size - 1) {
+ off += scnprintf(buf+off, size-off, "\n");
+ seq_commit(sf, off);
+ } else {
+ seq_commit(sf, -1);
+ }
}
}
