Commit dd87cc63 authored Jun 13, 2019 by Tejun Heo Committed by Greg Kroah-Hartman Jul 26, 2019

blkcg: update blkcg_print_stat() to handle larger outputs



commit f539da82f2158916e154d206054e0efd5df7ab61 upstream.

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: 903d23f0 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 73efdc5d

block/blk-cgroup.c

+6 −2

Original line number	Diff line number	Diff line
		@@ -1016,8 +1016,12 @@ static int blkcg_print_stat(struct seq_file sf, void v)
		}
		next:
		if (has_stats) {
		if (off < size - 1) {
		off += scnprintf(buf+off, size-off, "\n");
		seq_commit(sf, off);
		} else {
		seq_commit(sf, -1);
		}
		}
		}