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From: Peter Zijlstra <peterz@infradead.org>
To: gor@linux.ibm.com, jpoimboe@redhat.com, jikos@kernel.org,
	mbenes@suse.cz, pmladek@suse.com, mingo@kernel.org
Cc: linux-kernel@vger.kernel.org, peterz@infradead.org,
	joe.lawrence@redhat.com, fweisbec@gmail.com, tglx@linutronix.de,
	hca@linux.ibm.com, svens@linux.ibm.com, sumanthk@linux.ibm.com,
	live-patching@vger.kernel.org, paulmck@kernel.org,
	rostedt@goodmis.org, x86@kernel.org
Subject: [RFC][PATCH v2 10/11] livepatch: Remove klp_synchronize_transition()
Date: Wed, 29 Sep 2021 17:17:33 +0200	[thread overview]
Message-ID: <20210929152429.125997206@infradead.org> (raw)
In-Reply-To: <20210929151723.162004989@infradead.org>

The whole premise is broken, any trace usage outside of RCU is a BUG
and should be fixed. Notable all code prior (and a fair bit after)
ct_user_exit() is noinstr and explicitly doesn't allow any tracing.

Use regular RCU, which has the benefit of actually respecting
NOHZ_FULL.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/livepatch/transition.c |   32 +++-----------------------------
 1 file changed, 3 insertions(+), 29 deletions(-)

--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -42,28 +42,6 @@ static void klp_transition_work_fn(struc
 static DECLARE_DELAYED_WORK(klp_transition_work, klp_transition_work_fn);
 
 /*
- * This function is just a stub to implement a hard force
- * of synchronize_rcu(). 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 ct_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.
  */
@@ -96,7 +74,7 @@ static void klp_complete_transition(void
 		 * func->transition gets cleared, the handler may choose a
 		 * removed function.
 		 */
-		klp_synchronize_transition();
+		synchronize_rcu();
 	}
 
 	klp_for_each_object(klp_transition_patch, obj)
@@ -105,7 +83,7 @@ static void klp_complete_transition(void
 
 	/* Prevent klp_ftrace_handler() from seeing KLP_UNDEFINED state */
 	if (klp_target_state == KLP_PATCHED)
-		klp_synchronize_transition();
+		synchronize_rcu();
 
 	read_lock(&tasklist_lock);
 	for_each_process_thread(g, task) {
@@ -168,10 +146,6 @@ noinstr void __klp_update_patch_state(st
  */
 void klp_update_patch_state(struct task_struct *task)
 {
-	/*
-	 * A variant of synchronize_rcu() is used to allow patching functions
-	 * where RCU is not watching, see klp_synchronize_transition().
-	 */
 	preempt_disable_notrace();
 
 	/*
@@ -626,7 +600,7 @@ 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 */
-	klp_synchronize_transition();
+	synchronize_rcu();
 
 	klp_start_transition();
 }



  parent reply	other threads:[~2021-09-29 16:08 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-29 15:17 [PATCH v2 00/11] sched,rcu,context_tracking,livepatch: Improve livepatch task transitions for idle and NOHZ_FULL Peter Zijlstra
2021-09-29 15:17 ` [PATCH v2 01/11] sched: Improve try_invoke_on_locked_down_task() Peter Zijlstra
2021-10-09 10:07   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-09-29 15:17 ` [PATCH v2 02/11] sched,rcu: Rework try_invoke_on_locked_down_task() Peter Zijlstra
2021-10-09 10:07   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-09-29 15:17 ` [PATCH v2 03/11] sched,livepatch: Use task_call_func() Peter Zijlstra
2021-10-05 11:40   ` Petr Mladek
2021-10-05 14:03     ` Peter Zijlstra
2021-10-06  8:59   ` Miroslav Benes
2021-10-09 10:07   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-09-29 15:17 ` [PATCH v2 04/11] sched: Simplify wake_up_*idle*() Peter Zijlstra
2021-10-09 10:07   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-10-13 14:32   ` [PATCH v2 04/11] " Qian Cai
2021-10-19  3:47     ` Qian Cai
2021-10-19  8:56       ` Peter Zijlstra
2021-10-19  9:10         ` Peter Zijlstra
2021-10-19 15:32           ` Qian Cai
2021-10-19 15:50             ` Peter Zijlstra
2021-10-19 19:22               ` Qian Cai
2021-10-19 20:27                 ` Peter Zijlstra
     [not found]   ` <CGME20211022134630eucas1p2e79e2816587d182c580459d567c1f2a9@eucas1p2.samsung.com>
2021-10-22 13:46     ` Marek Szyprowski
2021-09-29 15:17 ` [PATCH v2 05/11] sched,livepatch: Use wake_up_if_idle() Peter Zijlstra
2021-10-05 12:00   ` Petr Mladek
2021-10-06  9:16   ` Miroslav Benes
2021-10-07  9:18     ` Vasily Gorbik
2021-10-07 10:02       ` Peter Zijlstra
2021-10-13 19:37   ` Arnd Bergmann
2021-10-14 10:42     ` Peter Zijlstra
2021-09-29 15:17 ` [RFC][PATCH v2 06/11] context_tracking: Prefix user_{enter,exit}*() Peter Zijlstra
2021-09-29 15:17 ` [RFC][PATCH v2 07/11] context_tracking: Add an atomic sequence/state count Peter Zijlstra
2021-09-29 15:17 ` [RFC][PATCH v2 08/11] context_tracking,rcu: Replace RCU dynticks counter with context_tracking Peter Zijlstra
2021-09-29 18:37   ` Paul E. McKenney
2021-09-29 19:09     ` Peter Zijlstra
2021-09-29 19:11     ` Peter Zijlstra
2021-09-29 19:13     ` Peter Zijlstra
2021-09-29 19:24       ` Peter Zijlstra
2021-09-29 19:45         ` Paul E. McKenney
2021-09-29 18:54   ` Peter Zijlstra
2021-09-29 15:17 ` [RFC][PATCH v2 09/11] context_tracking,livepatch: Dont disturb NOHZ_FULL Peter Zijlstra
2021-10-06  8:12   ` Petr Mladek
2021-10-06  9:04     ` Peter Zijlstra
2021-10-06 10:29       ` Petr Mladek
2021-10-06 11:41         ` Peter Zijlstra
2021-10-06 11:48         ` Miroslav Benes
2021-09-29 15:17 ` Peter Zijlstra [this message]
2021-10-06 12:30   ` [RFC][PATCH v2 10/11] livepatch: Remove klp_synchronize_transition() Petr Mladek
2021-09-29 15:17 ` [RFC][PATCH v2 11/11] context_tracking,x86: Fix text_poke_sync() vs NOHZ_FULL Peter Zijlstra
2021-10-21 18:39   ` Marcelo Tosatti
2021-10-21 18:40     ` Marcelo Tosatti
2021-10-21 19:25     ` Peter Zijlstra
2021-10-21 19:57       ` Marcelo Tosatti
2021-10-21 20:18         ` Peter Zijlstra
2021-10-26 18:19           ` Marcelo Tosatti
2021-10-26 19:38             ` Peter Zijlstra
2021-09-29 18:03 ` [PATCH v2 00/11] sched,rcu,context_tracking,livepatch: Improve livepatch task transitions for idle and NOHZ_FULL Paul E. McKenney
2021-10-09 10:07 ` [tip: sched/core] sched,livepatch: Use wake_up_if_idle() tip-bot2 for Peter Zijlstra
2021-10-14 11:16 ` tip-bot2 for Peter Zijlstra

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