On Wed, 16 Feb 2022, David Vernet wrote: > livepatch has a set of selftests that are used to validate the behavior of > the livepatching subsystem. One of the testcases in the livepatch > testsuite is test-ftrace.sh, which among other things, validates that > livepatching gracefully fails when ftrace is disabled. In the event that > ftrace cannot be disabled using 'sysctl kernel.ftrace_enabled=0', the test > will fail later due to it unexpectedly successfully loading the > test_klp_livepatch module. > > While the livepatch selftests are careful to remove any of the livepatch > test modules between testcases to avoid this situation, ftrace may still > fail to be disabled if another trace is active on the system that was > enabled with FTRACE_OPS_FL_PERMANENT. For example, any active BPF programs > that use trampolines will cause this test to fail due to the trampoline > being implemented with register_ftrace_direct(). The following is an > example of such a trace: > > tcp_drop (1) R I D tramp: ftrace_regs_caller+0x0/0x58 > (call_direct_funcs+0x0/0x30) > direct-->bpf_trampoline_6442550536_0+0x0/0x1000 > > In order to make the test more resilient to system state that is out of its > control, this patch updates set_ftrace_enabled() to detect sysctl failures, > and skip the testrun when appropriate. > > Suggested-by: Petr Mladek <pmladek@xxxxxxxx> > Signed-off-by: David Vernet <void@xxxxxxxxxxxxx> Acked-by: Miroslav Benes <mbenes@xxxxxxx> M
