Hello, with the glibc self-tests I was able to trigger the "this should not happen" warning ;) below on s390 (with panic_on_warn=1 set). It looks like it is hardly reproducible. This one happened with commit d146194f31c9 for compiling the kernel. Config can be re-created with "make ARCH=s390 performance_defconfig". [ 649.596938] WARNING: CPU: 0 PID: 58886 at kernel/futex.c:1418 do_futex+0xa9a/0xc50 [ 649.596946] Kernel panic - not syncing: panic_on_warn set ... [ 649.596951] CPU: 0 PID: 58886 Comm: ld64.so.1 Not tainted 4.20.0-20181125.rc3.git0.d146194f31c9.300.fc29.s390x+git #1 [ 649.596953] Hardware name: IBM 2964 NC9 702 (z/VM 6.4.0) [ 649.596956] Call Trace: [ 649.596963] ([<0000000000113050>] show_stack+0x58/0x70) [ 649.596970] [<0000000000a62a92>] dump_stack+0x7a/0xa8 [ 649.596975] [<0000000000144012>] panic+0x11a/0x258 [ 649.596978] [<0000000000143e70>] __warn+0xf8/0x118 [ 649.596981] [<0000000000a61c20>] report_bug+0xd8/0x150 [ 649.596985] [<00000000001014ac>] do_report_trap+0xc4/0xe0 [ 649.596988] [<0000000000101680>] illegal_op+0x138/0x150 [ 649.596994] [<0000000000a82bec>] pgm_check_handler+0x1cc/0x220 [ 649.596998] [<00000000001e89b2>] do_futex+0xa9a/0xc50 [ 649.597002] ([<00000000001e8b16>] do_futex+0xbfe/0xc50) [ 649.597006] [<00000000001e8c4c>] sys_futex+0xe4/0x170 [ 649.597010] [<0000000000a82800>] system_call+0xdc/0x2c8 Thanks, Heiko
