linux-kernel - Re: [PATCH 5/5] lockdep,x86: account for irqs enabled in paranoid

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Date:	Sat, 18 Apr 2009 09:00:15 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlsta <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 5/5] lockdep,x86: account for irqs enabled in
	paranoid_exit


* Steven Rostedt <rostedt@...dmis.org> wrote:

> From: Steven Rostedt <srostedt@...hat.com>
> 
> I hit the check_flags error of lockdep:
> 
> WARNING: at kernel/lockdep.c:2893 check_flags+0x1a7/0x1d0()
> [...]
> hardirqs last  enabled at (12567): [<ffffffff8026206a>] local_bh_enable+0xaa/0x110
> hardirqs last disabled at (12569): [<ffffffff80610c76>] int3+0x16/0x40
> softirqs last  enabled at (12566): [<ffffffff80514d2b>] lock_sock_nested+0xfb/0x110
> softirqs last disabled at (12568): [<ffffffff8058454e>] tcp_prequeue_process+0x2e/0xa0
> 
> The check_flags warning of lockdep tells me that lockdep thought interrupts
> were disabled, but they were really enabled.
> 
> The numbers in the above parenthesis show the order of events:
> 
> 12566: softirqs last enabled:  lock_sock_nested
> 12567: hardirqs last enabled:  local_bh_enable
> 12568: softirqs last disabled: tcp_prequeue_process
> 12566: hardirqs last disabled: int3
> 
> int3 is a breakpoint!
> 
> Examining this further, I have CONFIG_NET_TCPPROBE enabled which adds
> break points into the kernel.
> 
> The paranoid_exit of the return of int3 does not account for enabling
> interrupts on return to kernel. This code is a bit tricky since it
> is also used by the nmi handler (when lockdep is off), and we must be
> careful about the swapgs. We can not call kernel code after the swapgs
> has been performed.
> 
> [ Impact: fix lockdep check_flags warning ]
> 
> Acked-by: Peter Zijlsta <a.p.zijlstra@...llo.nl>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> ---
>  arch/x86/kernel/entry_64.S |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
> index 1ac9986..987f91f 100644
> --- a/arch/x86/kernel/entry_64.S
> +++ b/arch/x86/kernel/entry_64.S
> @@ -1397,7 +1397,10 @@ ENTRY(paranoid_exit)
>  paranoid_swapgs:
>  	TRACE_IRQS_IRETQ 0
>  	SWAPGS_UNSAFE_STACK
> +	RESTORE_ALL 8
> +	jmp irq_return
>  paranoid_restore:
> +	TRACE_IRQS_IRETQ 0
>  	RESTORE_ALL 8
>  	jmp irq_return
>  paranoid_userspace:

Nice catch! This is also for upstream really - i'll cherry-pick it 
into the lockdep urgent queue as well.

	Ingo
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