linux-kernel - Re: [PATCH] usbhid: Fix lockdep unannotated irqs-off warning

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Date:	Mon, 7 Mar 2016 18:15:49 +0100
From:	Sedat Dilek <sedat.dilek@...il.com>
To:	Jiri Kosina <jikos@...nel.org>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Tejun Heo <tj@...nel.org>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Benjamin Tissoires <benjamin.tissoires@...hat.com>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Andy Lutomirski <luto@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	USB list <linux-usb@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] usbhid: Fix lockdep unannotated irqs-off warning

On Mon, Mar 7, 2016 at 6:05 PM, Jiri Kosina <jikos@...nel.org> wrote:
> On Mon, 7 Mar 2016, Alan Stern wrote:
>
>> >      319:       9c                      pushfq
>> >      31a:       41 5c                   pop    %r12
>> >      31c:       48 89 df                mov    %rbx,%rdi
>> >      31f:       e8 00 00 00 00          callq  324 <usbhid_close+0x44>
>> >      324:       41 54                   push   %r12
>> >      326:       9d                      popfq
>>
>> spin_unlock_irq(&usbhid->lock); while attempting to preserve the Z
>> flag.  The problem is that this code sequence will also preserve the
>> Interrupt Flag!
>
> You are right Alan, thanks a lot, for reason I could not understand I
> completely missed the pushf/popf last time I was looking at the generated
> assembly!
>
> OK, a little bit of googling revealed related discussion on LLVM
> mailinglist:
>
>         http://lists.llvm.org/pipermail/llvm-dev/2015-July/088780.html
>
> Seems like it has been reported already, but noone dared to fix it yet.
>
> This basically makes LLVM unusable for compiling the kernel.
>

OK, OK.

Did someone look at the next/follow-ups in this thread?
For example: D6629 "x86: Emit LAHF/SAHF instead of PUSHF/POPF" [2]?

- Sedat -

[1] http://lists.llvm.org/pipermail/llvm-dev/2015-July/088874.html
[2] http://reviews.llvm.org/D6629