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From: Peter Zijlstra <peterz@infradead.org>
To: Waiman Long <longman@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Ingo Molnar <mingo@redhat.com>, Will Deacon <will.deacon@arm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
	the arch/x86 maintainers <x86@kernel.org>,
	Davidlohr Bueso <dave@stgolabs.net>,
	Tim Chen <tim.c.chen@linux.intel.com>,
	huang ying <huang.ying.caritas@gmail.com>,
	Roman Gushchin <guro@fb.com>, Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Steven Rostedt <rostedt@goodmis.org>
Subject: [PATCH] trace: Fix preempt_enable_no_resched() abuse
Date: Tue, 23 Apr 2019 22:03:18 +0200
Message-ID: <20190423200318.GY14281@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190423195559.GY4038@hirez.programming.kicks-ass.net>

On Tue, Apr 23, 2019 at 09:55:59PM +0200, Peter Zijlstra wrote:
> On Tue, Apr 23, 2019 at 03:41:32PM -0400, Waiman Long wrote:

> > I saw a number of instances of
> > preempt_enable_no_resched() without right next a schedule().
> 
> Look more closely.. and let me know, if true, those are bugs that need
> fixing.
> 
> Argghhh.. BPF...

/me shakes head, Steve...

---
Subject: trace: Fix preempt_enable_no_resched() abuse

Unless the very next line is schedule(), or implies it, one must not use
preempt_enable_no_resched(). It can cause a preemption to go missing and
thereby cause arbitrary delays, breaking the PREEMPT=y invariant.

Cc: Steven Rostedt <rostedt@goodmis.org>
Fixes: 37886f6a9f62 ("ring-buffer: add api to allow a tracer to change clock source")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/trace/ring_buffer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 41b6f96e5366..4ee8d8aa3d0f 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -762,7 +762,7 @@ u64 ring_buffer_time_stamp(struct ring_buffer *buffer, int cpu)
 
 	preempt_disable_notrace();
 	time = rb_time_stamp(buffer);
-	preempt_enable_no_resched_notrace();
+	preempt_enable_notrace();
 
 	return time;
 }

  reply index

Thread overview: 112+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-13 17:22 [PATCH v4 00/16] locking/rwsem: Rwsem rearchitecture part 2 Waiman Long
2019-04-13 17:22 ` [PATCH v4 01/16] locking/rwsem: Prevent unneeded warning during locking selftest Waiman Long
2019-04-18  8:04   ` [tip:locking/core] " tip-bot for Waiman Long
2019-04-13 17:22 ` [PATCH v4 02/16] locking/rwsem: Make owner available even if !CONFIG_RWSEM_SPIN_ON_OWNER Waiman Long
2019-04-13 17:22 ` [PATCH v4 03/16] locking/rwsem: Remove rwsem_wake() wakeup optimization Waiman Long
2019-04-13 17:22 ` [PATCH v4 04/16] locking/rwsem: Implement a new locking scheme Waiman Long
2019-04-16 13:22   ` Peter Zijlstra
2019-04-16 13:32     ` Waiman Long
2019-04-16 14:18       ` Peter Zijlstra
2019-04-16 14:42         ` Peter Zijlstra
2019-04-13 17:22 ` [PATCH v4 05/16] locking/rwsem: Merge rwsem.h and rwsem-xadd.c into rwsem.c Waiman Long
2019-04-13 17:22 ` [PATCH v4 06/16] locking/rwsem: Code cleanup after files merging Waiman Long
2019-04-16 16:01   ` Peter Zijlstra
2019-04-16 16:17     ` Peter Zijlstra
2019-04-16 19:45       ` Waiman Long
2019-04-13 17:22 ` [PATCH v4 07/16] locking/rwsem: Implement lock handoff to prevent lock starvation Waiman Long
2019-04-16 14:12   ` Peter Zijlstra
2019-04-16 20:26     ` Waiman Long
2019-04-16 21:07       ` Waiman Long
2019-04-17  7:13         ` Peter Zijlstra
2019-04-17 16:22           ` Waiman Long
2019-04-16 15:49   ` Peter Zijlstra
2019-04-16 16:15     ` Peter Zijlstra
2019-04-16 18:41       ` Waiman Long
2019-04-16 18:16     ` Waiman Long
2019-04-16 18:32       ` Peter Zijlstra
2019-04-17  7:35       ` Peter Zijlstra
2019-04-17 16:35         ` Waiman Long
2019-04-17  8:05       ` Peter Zijlstra
2019-04-17 16:39         ` Waiman Long
2019-04-18  8:22           ` Peter Zijlstra
2019-04-17  8:17   ` Peter Zijlstra
2019-04-13 17:22 ` [PATCH v4 08/16] locking/rwsem: Make rwsem_spin_on_owner() return owner state Waiman Long
2019-04-17  9:00   ` Peter Zijlstra
2019-04-17 16:42     ` Waiman Long
2019-04-17 10:19   ` Peter Zijlstra
2019-04-17 16:53     ` Waiman Long
2019-04-17 12:41   ` Peter Zijlstra
2019-04-17 12:47     ` Peter Zijlstra
2019-04-17 18:29       ` Waiman Long
2019-04-18  8:39         ` Peter Zijlstra
2019-04-17 13:00     ` Peter Zijlstra
2019-04-17 18:50       ` Waiman Long
2019-04-13 17:22 ` [PATCH v4 09/16] locking/rwsem: Ensure an RT task will not spin on reader Waiman Long
2019-04-17 13:18   ` Peter Zijlstra
2019-04-17 18:47     ` Waiman Long
2019-04-18  8:52       ` Peter Zijlstra
2019-04-18 13:27         ` Waiman Long
2019-04-13 17:22 ` [PATCH v4 10/16] locking/rwsem: Wake up almost all readers in wait queue Waiman Long
2019-04-16 16:50   ` Davidlohr Bueso
2019-04-16 17:37     ` Waiman Long
2019-04-17 13:39   ` Peter Zijlstra
2019-04-17 17:16     ` Waiman Long
2019-04-13 17:22 ` [PATCH v4 11/16] locking/rwsem: Enable readers spinning on writer Waiman Long
2019-04-17 13:56   ` Peter Zijlstra
2019-04-17 17:34     ` Waiman Long
2019-04-18  8:57       ` Peter Zijlstra
2019-04-18 14:35         ` Waiman Long
2019-04-17 13:58   ` Peter Zijlstra
2019-04-17 17:45     ` Waiman Long
2019-04-18  9:00       ` Peter Zijlstra
2019-04-18 13:40         ` Waiman Long
2019-04-17 14:05   ` Peter Zijlstra
2019-04-17 17:51     ` Waiman Long
2019-04-18  9:11       ` Peter Zijlstra
2019-04-18 14:37         ` Waiman Long
2019-04-13 17:22 ` [PATCH v4 12/16] locking/rwsem: Enable time-based spinning on reader-owned rwsem Waiman Long
2019-04-18 13:06   ` Peter Zijlstra
2019-04-18 15:15     ` Waiman Long
2019-04-19  7:56       ` Peter Zijlstra
2019-04-19 14:33         ` Waiman Long
2019-04-19 15:36           ` Waiman Long
2019-04-13 17:22 ` [PATCH v4 13/16] locking/rwsem: Add more rwsem owner access helpers Waiman Long
2019-04-13 17:22 ` [PATCH v4 14/16] locking/rwsem: Guard against making count negative Waiman Long
2019-04-18 13:51   ` Peter Zijlstra
2019-04-18 14:08     ` Waiman Long
2019-04-18 14:30       ` Peter Zijlstra
2019-04-18 14:40       ` Peter Zijlstra
2019-04-18 14:54         ` Waiman Long
2019-04-19 10:26           ` Peter Zijlstra
2019-04-19 12:02             ` Peter Zijlstra
2019-04-19 13:03               ` Peter Zijlstra
2019-04-19 13:15                 ` Peter Zijlstra
2019-04-19 19:39                   ` Waiman Long
2019-04-21 21:07                     ` Waiman Long
2019-04-23 14:17                       ` Peter Zijlstra
2019-04-23 14:31                         ` Waiman Long
2019-04-23 16:27                         ` Linus Torvalds
2019-04-23 19:12                           ` Waiman Long
2019-04-23 19:34                             ` Peter Zijlstra
2019-04-23 19:41                               ` Waiman Long
2019-04-23 19:55                                 ` [PATCH] bpf: Fix preempt_enable_no_resched() abuse Peter Zijlstra
2019-04-23 20:03                                   ` Peter Zijlstra [this message]
2019-04-23 23:58                                     ` [PATCH] trace: " Steven Rostedt
2019-04-29  6:39                                     ` [tip:sched/core] " tip-bot for Peter Zijlstra
2019-04-29 13:31                                       ` Steven Rostedt
2019-04-29 14:08                                         ` Ingo Molnar
2019-04-23 20:27                                   ` [PATCH] bpf: " Linus Torvalds
2019-04-23 20:35                                     ` Peter Zijlstra
2019-04-23 20:45                                       ` Linus Torvalds
2019-04-24 13:19                                       ` Peter Zijlstra
2019-04-25 21:23                                   ` Alexei Starovoitov
2019-04-26  7:14                                     ` Peter Zijlstra
2019-04-24  7:09                             ` [PATCH v4 14/16] locking/rwsem: Guard against making count negative Peter Zijlstra
2019-04-24 16:49                               ` Waiman Long
2019-04-24 17:01                                 ` Peter Zijlstra
2019-04-24 17:10                                   ` Waiman Long
2019-04-24 17:56                                   ` Linus Torvalds
2019-04-13 17:22 ` [PATCH v4 15/16] locking/rwsem: Merge owner into count on x86-64 Waiman Long
2019-04-18 14:28   ` Peter Zijlstra
2019-04-18 14:40     ` Waiman Long
2019-04-13 17:22 ` [PATCH v4 16/16] locking/rwsem: Remove redundant computation of writer lock word Waiman Long

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