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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
This commit is contained in:
Linus Torvalds 2017-06-21 12:02:48 -07:00
parent 021f601980 842c088464
commit dcba71086e
2 changed files with 37 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
kernel/livepatch/patch.c
View File

@ -59,7 +59,11 @@ static void notrace klp_ftrace_handler(unsigned long ip,
ops = container_of(fops, struct klp_ops, fops); 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, func = list_first_or_null_rcu(&ops->func_stack, struct klp_func,
stack_node); 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); klp_arch_set_pc(regs, (unsigned long)func->new_func);
unlock: unlock:
rcu_read_unlock(); preempt_enable_notrace();
} }
/* /*

36
kernel/livepatch/transition.c
View File

@ -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); 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 * The transition to the target patch state is complete. Clean up the data
* structures. * structures.
@ -73,7 +95,7 @@ static void klp_complete_transition(void)
* func->transition gets cleared, the handler may choose a * func->transition gets cleared, the handler may choose a
* removed function. * removed function.
*/ */
synchronize_rcu(); klp_synchronize_transition();
} }
if (klp_transition_patch->immediate) if (klp_transition_patch->immediate)
@ -92,7 +114,7 @@ static void klp_complete_transition(void)
/* Prevent klp_ftrace_handler() from seeing KLP_UNDEFINED state */ /* Prevent klp_ftrace_handler() from seeing KLP_UNDEFINED state */
if (klp_target_state == KLP_PATCHED) if (klp_target_state == KLP_PATCHED)
synchronize_rcu(); klp_synchronize_transition();
read_lock(&tasklist_lock); read_lock(&tasklist_lock);
for_each_process_thread(g, task) { for_each_process_thread(g, task) {
@ -136,7 +158,11 @@ void klp_cancel_transition(void)
*/ */
void klp_update_patch_state(struct task_struct *task) 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 * 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)) if (test_and_clear_tsk_thread_flag(task, TIF_PATCH_PENDING))
task->patch_state = READ_ONCE(klp_target_state); 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); clear_tsk_thread_flag(idle_task(cpu), TIF_PATCH_PENDING);
/* Let any remaining calls to klp_update_patch_state() complete */ /* Let any remaining calls to klp_update_patch_state() complete */
synchronize_rcu(); klp_synchronize_transition();
klp_start_transition(); klp_start_transition();
} }