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Commit dcba7108 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/livepatching 

Pull livepatching fix from Jiri Kosina:
 "Fix the way how livepatches are being stacked with respect to RCU,
  from Petr Mladek"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/livepatching:
  livepatch: Fix stacking of patches with respect to RCU
parents 021f6019 842c0884

kernel/livepatch/patch.c

+6 −2
Original line number Diff line number Diff line
@@ -59,7 +59,11 @@ static void notrace klp_ftrace_handler(unsigned long ip, 


	ops = container_of(fops, struct klp_ops, fops);



	rcu_read_lock();

	/*

	 * A variant of synchronize_sched() is used to allow patching functions

	 * where RCU is not watching, see klp_synchronize_transition().

	 */

	preempt_disable_notrace();



	func = list_first_or_null_rcu(&ops->func_stack, struct klp_func,

				      stack_node);
@@ -115,7 +119,7 @@ static void notrace klp_ftrace_handler(unsigned long ip, 


	klp_arch_set_pc(regs, (unsigned long)func->new_func);

unlock:

	rcu_read_unlock();

	preempt_enable_notrace();

}



/*

kernel/livepatch/transition.c

+31 −5
Original line number Diff line number Diff line
@@ -48,6 +48,28 @@ static void klp_transition_work_fn(struct work_struct *work) 
}

static DECLARE_DELAYED_WORK(klp_transition_work, klp_transition_work_fn);



/*

 * This function is just a stub to implement a hard force

 * of synchronize_sched(). This requires synchronizing

 * tasks even in userspace and idle.

 */

static void klp_sync(struct work_struct *work)

{

}



/*

 * We allow to patch also functions where RCU is not watching,

 * e.g. before user_exit(). We can not rely on the RCU infrastructure

 * to do the synchronization. Instead hard force the sched synchronization.

 *

 * This approach allows to use RCU functions for manipulating func_stack

 * safely.

 */

static void klp_synchronize_transition(void)

{

	schedule_on_each_cpu(klp_sync);

}



/*

 * The transition to the target patch state is complete.  Clean up the data

 * structures.
@@ -73,7 +95,7 @@ static void klp_complete_transition(void) 
		 * func->transition gets cleared, the handler may choose a

		 * removed function.

		 */

		synchronize_rcu();

		klp_synchronize_transition();

	}



	if (klp_transition_patch->immediate)
@@ -92,7 +114,7 @@ static void klp_complete_transition(void) 


	/* Prevent klp_ftrace_handler() from seeing KLP_UNDEFINED state */

	if (klp_target_state == KLP_PATCHED)

		synchronize_rcu();

		klp_synchronize_transition();



	read_lock(&tasklist_lock);

	for_each_process_thread(g, task) {
@@ -136,7 +158,11 @@ void klp_cancel_transition(void) 
 */

void klp_update_patch_state(struct task_struct *task)

{

	rcu_read_lock();

	/*

	 * A variant of synchronize_sched() is used to allow patching functions

	 * where RCU is not watching, see klp_synchronize_transition().

	 */

	preempt_disable_notrace();



	/*

	 * This test_and_clear_tsk_thread_flag() call also serves as a read
@@ -153,7 +179,7 @@ void klp_update_patch_state(struct task_struct *task) 
	if (test_and_clear_tsk_thread_flag(task, TIF_PATCH_PENDING))

		task->patch_state = READ_ONCE(klp_target_state);



	rcu_read_unlock();

	preempt_enable_notrace();

}



/*
@@ -539,7 +565,7 @@ void klp_reverse_transition(void) 
		clear_tsk_thread_flag(idle_task(cpu), TIF_PATCH_PENDING);



	/* Let any remaining calls to klp_update_patch_state() complete */

	synchronize_rcu();

	klp_synchronize_transition();



	klp_start_transition();

}