From 332b302f92b67cb509ad30d9c930825c5c0c3270 Mon Sep 17 00:00:00 2001 From: normal Date: Mon, 20 Aug 2018 01:43:10 +0000 Subject: spec/ruby/core/io/select_spec.rb: workaround stuck IO.select Under pipe page memory pressure on Linux, a pipe may only be created with a single buffer[1]. And as of Linux v4.18, the fs/pipe.c::pipe_poll callback does not account for merging done in fs/pipe::pipe_write; only the number of usable buffers in the pipe. Thus it is possible for a pipe to be writable (if only by a small amount) despite IO.select saying it is not. With the default 16384 /proc/sys/fs/pipe-user-pages-soft value and the pipe having 16 pages of buffers, this issue is trivially reproducible by creating 1024 pipes in a background process before running the spec: $ ulimit -n 2053 # or something higher $ ./miniruby -e '1024.times.map { IO.pipe }; sleep' & $ make test-spec MSPECOPT=spec/ruby/core/io/select_spec.rb So, we create a new pipe we never write to for testing writability of IO.select. This may cause the test to fail with ENFILE on an overloaded system, but at least that's an obvious failure (unlike having a test get stuck). This should reduce failures on our overloaded CI machines: http://ci.rvm.jp/results/trunk-nopara@silicon-docker/1239426 [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/pipe.c?h=v4.18#n642 git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@64478 b2dd03c8-39d4-4d8f-98ff-823fe69b080e --- spec/ruby/core/io/select_spec.rb | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) diff --git a/spec/ruby/core/io/select_spec.rb b/spec/ruby/core/io/select_spec.rb index 74371275c6..e69669efd2 100644 --- a/spec/ruby/core/io/select_spec.rb +++ b/spec/ruby/core/io/select_spec.rb @@ -16,8 +16,10 @@ describe "IO.select" do it "returns immediately all objects that are ready for I/O when timeout is 0" do @wr.syswrite("be ready") - result = IO.select [@rd], [@wr], nil, 0 - result.should == [[@rd], [@wr], []] + IO.pipe do |_, wr| + result = IO.select [@rd], [wr], nil, 0 + result.should == [[@rd], [wr], []] + end end it "returns nil after timeout if there are no objects ready for I/O" do @@ -70,9 +72,11 @@ describe "IO.select" do obj.should_receive(:to_io).at_least(1).and_return(@rd) IO.select([obj]).should == [[obj], [], []] - obj = mock("write_io") - obj.should_receive(:to_io).at_least(1).and_return(@wr) - IO.select(nil, [obj]).should == [[], [obj], []] + IO.pipe do |_, wr| + obj = mock("write_io") + obj.should_receive(:to_io).at_least(1).and_return(wr) + IO.select(nil, [obj]).should == [[], [obj], []] + end end it "raises TypeError if supplied objects are not IO" do -- cgit v1.2.3