On Mon 2018-03-05 13:54:38, Miroslav Benes wrote: > On Mon, 5 Mar 2018, Evgenii Shatokhin wrote: > > > Hi, > > Hi, > > > > The atomic replace allows to create cumulative patches. They > > > are useful when you maintain many livepatches and want to remove > > > one that is lower on the stack. In addition it is very useful when > > > more patches touch the same function and there are dependencies > > > between them. > > > > I have experimented with this updated patchset a bit. > > It looks like replace operation fails if there is a loaded but disabled > > patch. > > > > Suppose there are 2 binary patches changing the same kernel functions. Load > > patch1, then disable it (echo 0 > /sys/kernel/livepatch/patch1/enabled), > > then > > try load patch2 with atomic replace. I get "Device or resource busy" error > > at > > this point. > > > > It seems, __klp_enable_patch() returns -EBUSY for some reason. I haven't dug > > deeper into that code yet. > > Yes, it is "enforce stacking" check in __klp_enable_patch(): > > /* enforce stacking: only the first disabled patch can be enabled */ > if (patch->list.prev != &klp_patches && > !list_prev_entry(patch, list)->enabled) > return -EBUSY; > > So not connected to this patch set. We've had the behaviour for quite some > time.
We actually wanted to enabled this for the patches with the replace flag. It is even described in Documentation/livepatch/cumulative-patches.txt. Of course, you could always unregister all the disabled patches that block the new one. But it might be inconvenient. I do not see any big reason why this should be disabled: + klp_add_nops() takes into account even disabled patches. In the worst case, we might enable some NOPs that are not really needed. + klp_throw_away_replaced_patches() removes all patches down the stack. I am going to enable this in a separate patch in v10. Best Regards, Petr