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authorLinus Torvalds <torvalds@linux-foundation.org>2017-06-21 12:02:48 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2017-06-21 12:02:48 -0700
commitdcba71086e0d1abf4f00cd381530b11d0db7fa1d (patch)
tree8f89180f41c3592529b9bfecb77e63a683b414fb
parent021f601980ccf07e65bc03e40d0321243f782d34 (diff)
parent842c08846420baa619fe3cb8c9af538efdb89428 (diff)
downloadlinux-stericsson-dcba71086e0d1abf4f00cd381530b11d0db7fa1d.tar.gz
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
-rw-r--r--kernel/livepatch/patch.c8
-rw-r--r--kernel/livepatch/transition.c36
2 files changed, 37 insertions, 7 deletions
diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c
index f8269036bf0b..52c4e907c14b 100644
--- a/kernel/livepatch/patch.c
+++ b/kernel/livepatch/patch.c
@@ -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();
}
/*
diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index adc0cc64aa4b..b004a1fb6032 100644
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -49,6 +49,28 @@ 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();
}