88e1f16ba5
0Day/LKP observed that the kselftest blocks forever since one of the pidfd_wait doesn't terminate in 1 of 30 runs. After digging into the source, we found that it blocks at: ASSERT_EQ(sys_waitid(P_PIDFD, pidfd, &info, WCONTINUED, NULL), 0); wait_states has below testing flow: CHILD PARENT ---------------+-------------- 1 STOP itself 2 WAIT for CHILD STOPPED 3 SIGNAL CHILD to CONT 4 CONT 5 STOP itself 5' WAIT for CHILD CONT 6 WAIT for CHILD STOPPED The problem is that the kernel cannot ensure the order of 5 and 5', once 5 goes first, the test will fail. we can reproduce it by: $ while true; do make run_tests -C pidfd; done Introduce a blocking read in child process to make sure the parent can check its WCONTINUED. CC: Philip Li <philip.li@intel.com> Reported-by: kernel test robot <lkp@intel.com> Signed-off-by: Li Zhijian <lizhijian@fujitsu.com> Reviewed-by: Christian Brauner (Microsoft) <brauner@kernel.org> Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.