On Tue, 8 Oct 2019 15:35:34 -0400 Joe Lawrence <joe.lawrence@xxxxxxxxxx> wrote: > > I wonder if the opposite would be more intuitive: when ftrace_enabled is > not set, don't allow livepatches to register ftrace filters and > likewise, don't allow ftrace_enabled to be unset if any livepatches are > already registered. I guess you could make an argument either way, but > just offering another option. Perhaps livepatches should follow similar > behavior of other ftrace clients (like perf probes?) I believe I suggested the "PERMANENT" flag, but disabling ftrace_enable may be another approach. Might be much easier to maintain. > > As for the approach in this patchset, is it consistent that livepatches > loaded after setting ftrace_enabled to 0 will successfully load, but not > execute their new code... but then when ftrace_enabled is toggled, the > new livepatch code remains on? > > For example: > > 1 - Turn ftrace_enabled off and load the /proc/cmdline livepatch test > case, note that it reports a success patching transition, but > doesn't run new its code: > > % dmesg -C > % sysctl kernel.ftrace_enabled=0 > kernel.ftrace_enabled = 0 > % insmod lib/livepatch/test_klp_livepatch.ko > % echo $? > 0 > % dmesg > [ 450.579980] livepatch: enabling patch 'test_klp_livepatch' > [ 450.581243] livepatch: 'test_klp_livepatch': starting patching transition > [ 451.942971] livepatch: 'test_klp_livepatch': patching complete > % cat /proc/cmdline > BOOT_IMAGE=(hd0,msdos1)/boot/vmlinuz-5.4.0-rc2+ root=UUID=c42bb089-b5c1-4e17-82bd-132f55bee54c ro console=ttyS0 console=ttyS0,115200n8 no_timer_check net.ifnames=0 crashkernel=auto > > 2 - Turn ftrace_enabled on and see that the livepatch now works: > > % sysctl kernel.ftrace_enabled=1 > kernel.ftrace_enabled = 1 > % cat /proc/cmdline > test_klp_livepatch: this has been live patched > > 3 - Turn ftrace_enabled off and see that it's still enabled: > > % sysctl kernel.ftrace_enabled=0 > kernel.ftrace_enabled = 0 > % cat /proc/cmdline > test_klp_livepatch: this has been live patched > > Steps 2 and 3 match the behavior described by the patchset, but I was > particularly wondering what you thought about step 1. > > IMHO, I would expect step 1 to fully enable the livepatch, or at the > very least, not report a patch transition (though that may confuse > userspace tools waiting for that report). > I think I like your idea better. To prevent ftrace_enable from being disabled if a "permanent" option is set. Then we only need to have a permanent flag for the ftrace_ops, that will disable the ftrace_enable from being cleared. We can also prevent the ftrace_ops from being loaded if ftrace_enable is not set and the ftrace_ops has the PERMANENT flag set. -- Steve
