From mboxrd@z Thu Jan  1 00:00:00 1970
Subject: Re: Enable/Disable of ftrace events crashes kernel
References: <CAFLxGvzoCXUq_QFMT=b54nnLd8Oeu3XfFeiCKoCj3a0Q3Xg8yA@mail.gmail.com>
 <3b8bf95c-5170-d229-b27f-1577a2e0942b@siemens.com>
 <CAFLxGvzgCuoaG+O9EyiJZG_YD-2KQxVWd1LG-FepiEAjebqJnQ@mail.gmail.com>
From: Jan Kiszka <jan.kiszka@siemens.com>
Message-ID: <fb2a4587-5180-663b-1dee-e2b7b114fc63@siemens.com>
Date: Thu, 11 Jul 2019 20:30:55 +0200
MIME-Version: 1.0
In-Reply-To: <CAFLxGvzgCuoaG+O9EyiJZG_YD-2KQxVWd1LG-FepiEAjebqJnQ@mail.gmail.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
List-Id: Discussions about the Xenomai project <xenomai.xenomai.org>
List-Unsubscribe: <https://xenomai.org/mailman/options/xenomai>,
 <mailto:xenomai-request@xenomai.org?subject=unsubscribe>
List-Archive: <http://xenomai.org/pipermail/xenomai/>
List-Post: <mailto:xenomai@xenomai.org>
List-Help: <mailto:xenomai-request@xenomai.org?subject=help>
List-Subscribe: <https://xenomai.org/mailman/listinfo/xenomai>,
 <mailto:xenomai-request@xenomai.org?subject=subscribe>
To: Richard Weinberger <richard.weinberger@gmail.com>
Cc: xenomai@xenomai.org

On 11.07.19 12:25, Richard Weinberger wrote:
> On Thu, Jul 11, 2019 at 12:21 PM Jan Kiszka <jan.kiszka@siemens.com> wrote:
>> Can't reproduce so far, even with a while-true loop. Can you share your .config?
> 
> Sure, see attachment.
> 

This seems to fix the issue here:

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 119fd66d111e..8f647c208cf2 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -997,8 +997,8 @@ apicinterrupt IRQ_WORK_VECTOR			irq_work_interrupt		smp_irq_work_interrupt
 \skip_label:
 	UNWIND_HINT_REGS
 	DISABLE_INTERRUPTS(CLBR_ANY)
-	testl	%ebx, %ebx	/* %ebx: return to kernel mode */
-	jnz	retint_kernel_early
+	testb	$3, CS(%rsp)
+	jz	retint_kernel_early
 	jmp	retint_user_early
 	.endif
 1001:

Tests welcome!

Interestingly, 4.14 should have the same problem, but I failed to
reproduce there so far.

Jan

-- 
Siemens AG, Corporate Technology, CT RDA IOT SES-DE
Corporate Competence Center Embedded Linux