On Tue, 8 Oct 2019, Steven Rostedt wrote: > 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. You did. > > > > 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? No, it is not consistent and was not intended. > > 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). Yes. > > 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. Agreed. Joe's approach is better. Let me prepare v2. Thanks Miroslav
