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Date: Tue, 25 Oct 2011 18:14:26 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>, "H. Peter Anvin" <hpa@zytor.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Christoph Hellwig <hch@infradead.org>,
        Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
        Thomas Gleixner <tglx@linutronix.de>, Andi Kleen <andi@firstfloor.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Jim Keniston <jkenisto@linux.vnet.ibm.com>,
        Roland McGrath <roland@hack.frob.com>, Shuah Khan <shuah.khan@hp.com>,
        Ingo Molnar <mingo@elte.hu>,
        Alexander van Heukelum <heukelum@fastmail.fm>,
        Russell King <rmk@arm.linux.org.uk>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RESEND] [RFC][PATCH X86_32 1/2]: Call do_notify_resume() with
	interrupts enabled
Message-ID: <20111025161426.GC17067@redhat.com>
References: <20111025141812.GA21225@linux.vnet.ibm.com>
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On 10/25, Srikar Dronamraju wrote:
>
> do_notify_resume() gets called with interrupts disabled on x86_32. This
> is different from the x86_64 behavior, where interrupts are enabled at
> the time.

And note that do_notify_resume() paths assume that irqs are enabled.
key_replace_session_keyring/get_signal_to_deliver start with _lock_irq.

IOW, I vote for this change even if I can't ack it (although it looks
"obviously correct" to me). In fact refrigerator() looks buggy without
this change. Yes, it enables irqs but only "by accident", via unlock_irq().
And we are going to remove this recalc_sigpending() from freezer.


> Queries on lkml on this issue hasn't yielded any clear answer. Lets make
> x86_32 behave the same as x86_64, unless there is a real reason to
> maintain status quo.
> 
> Please refer https://lkml.org/lkml/2011/9/27/130 for more details
> 
> A similar change was suggested in arm
> 	https://lkml.org/lkml/2011/8/25/231
> 
> My 32-bit machine works fine (tm) with the patch below
> 
> Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
> ---
>  arch/x86/kernel/entry_32.S |    4 ++++
>  1 files changed, 4 insertions(+)
> 
> diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
> index f3f6f53..22d0e21 100644
> --- a/arch/x86/kernel/entry_32.S
> +++ b/arch/x86/kernel/entry_32.S
> @@ -625,6 +625,8 @@ work_notifysig:				# deal with pending signals and
>  	movl %esp, %eax
>  	jne work_notifysig_v86		# returning to kernel-space or
>  					# vm86-space
> +	TRACE_IRQS_ON
> +	ENABLE_INTERRUPTS(CLBR_NONE)
>  	xorl %edx, %edx
>  	call do_notify_resume
>  	jmp resume_userspace_sig
> @@ -638,6 +640,8 @@ work_notifysig:				# deal with pending signals and
>  #else
>  	movl %esp, %eax
>  #endif
> +	TRACE_IRQS_ON
> +	ENABLE_INTERRUPTS(CLBR_NONE)
>  	xorl %edx, %edx
>  	call do_notify_resume
>  	jmp resume_userspace_sig
>