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livepatch: Don't block the removal of patches loaded after a forced transition

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module_put() is currently never called in klp_complete_transition() when
klp_force is set. As a result, we might keep the reference count even when
klp_enable_patch() fails and klp_cancel_transition() is called.

This might give the impression that a module might get blocked in some
strange init state. Fortunately, it is not the case. The reference count
is ignored when mod->init fails and erroneous modules are always removed.

Anyway, this might be confusing. Instead, this patch moves
the global klp_forced flag into struct klp_patch. As a result,
we block only modules that might still be in use after a forced
transition. Newly loaded livepatches might be eventually completely
removed later.

It is not a big deal. But the code is at least consistent with
the reality.

Signed-off-by: Petr Mladek <pmladek@suse.com>
Acked-by: Joe Lawrence <joe.lawrence@redhat.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
This commit is contained in:
Petr Mladek 2019-01-09 13:43:22 +01:00 • committed by Jiri Kosina
parent 0430f78bf3
commit 68007289bf
4 changed files with 11 additions and 6 deletions
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10
kernel/livepatch/transition.c
View file

@ -33,8 +33,6 @@ struct klp_patch *klp_transition_patch;
static int klp_target_state = KLP_UNDEFINED;
static bool klp_forced = false;
/*
* This work can be performed periodically to finish patching or unpatching any
* "straggler" tasks which failed to transition in the first attempt.
@ -137,10 +135,10 @@ static void klp_complete_transition(void)
klp_target_state == KLP_PATCHED ? "patching" : "unpatching");
/*
* klp_forced set implies unbounded increase of module's ref count if
* patch->forced set implies unbounded increase of module's ref count if
* the module is disabled/enabled in a loop.
*/
if (!klp_forced && klp_target_state == KLP_UNPATCHED)
if (!klp_transition_patch->forced && klp_target_state == KLP_UNPATCHED)
module_put(klp_transition_patch->mod);
klp_target_state = KLP_UNDEFINED;
@ -620,6 +618,7 @@ void klp_send_signals(void)
*/
void klp_force_transition(void)
{
struct klp_patch *patch;
struct task_struct *g, *task;
unsigned int cpu;
@ -633,5 +632,6 @@ void klp_force_transition(void)
for_each_possible_cpu(cpu)
klp_update_patch_state(idle_task(cpu));
klp_forced = true;
list_for_each_entry(patch, &klp_patches, list)
patch->forced = true;
}