From: Tejun Heo tj@kernel.org
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: 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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- block/blk-cgroup.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)
--- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -1005,8 +1005,12 @@ static int blkcg_print_stat(struct seq_f } 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); + } } }