On Fri, Oct 02, 2020 at 11:01:34PM +0530, Naresh Kamboju wrote:
On Thu, 24 Sep 2020 at 21:51, Christian Brauner firstname.lastname@example.org wrote:
On Thu, Sep 24, 2020 at 04:33:17PM +0200, Christian Brauner wrote:
On Wed, Sep 23, 2020 at 07:52:05PM +0530, Naresh Kamboju wrote:
selftests: pidfd: pidfd_wait hangs on linux next kernel on x86_64, i386 and arm64 Juno-r2 These devices are using NFS mounted rootfs. I have tested pidfd testcases independently and all test PASS.
The Hang or exit from test run noticed when run by run_kselftest.sh
pidfd_wait.c:208:wait_nonblock:Expected sys_waitid(P_PIDFD, pidfd, &info, WSTOPPED, NULL) (-1) == 0 (0) wait_nonblock: Test terminated by assertion
metadata: git branch: master git repo: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git git commit: e64997027d5f171148687e58b78c8b3c869a6158 git describe: next-20200922 make_kernelversion: 5.9.0-rc6 kernel-config: http://snapshots.linaro.org/openembedded/lkft/lkft/sumo/intel-core2-32/lkft/...
Reported-by: Naresh Kamboju email@example.com
Thanks for reproting this. I'm taking a look now!
Ok, this is a simple race in the selftests, that I overlooked and which is more likely to hit when there's a lot of processes running on the system. Basically the child process hasn't SIGSTOPed itself yet but the parent is already calling waitid() on a O_NONBLOCK pidfd. Since it doesn't find a WSTOPPED process it returns -EAGAIN correctly.
The fix for this is to move the line where we're removing the O_NONBLOCK property from the fd before the waitid() WSTOPPED call so we hang until the child becomes stopped.
So I believe the fix is:
I have tested this patch and the pidfd_wait test did not hang this time.
Tested-by: Naresh Kamboju firstname.lastname@example.org
test log link https://lkft.validation.linaro.org/scheduler/job/1813223
Thanks for testing, Naresh. I've applied the patch: https://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux.git/commit/?h=...