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

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Message-ID: <20160302113535.6abe9a2c@gandalf.local.home>
Date:	Wed, 2 Mar 2016 11:35:35 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Sedat Dilek <sedat.dilek@...il.com>,
	Jiri Kosina <jikos@...nel.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>, linux-usb@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Felipe Balbi <balbi@...com>, Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] usbhid: Fix lockdep unannotated irqs-off warning

On Wed, 2 Mar 2016 17:24:12 +0100
Peter Zijlstra <peterz@...radead.org> wrote:

> On Wed, Mar 02, 2016 at 04:53:36PM +0100, Sedat Dilek wrote:
> > ffffffff8110f570 <del_timer_sync>:
> > ffffffff8110f570:	55                   	push   %rbp
> > ffffffff8110f571:	48 89 e5             	mov    %rsp,%rbp
> > ffffffff8110f574:	41 57                	push   %r15
> > ffffffff8110f576:	41 56                	push   %r14
> > ffffffff8110f578:	53                   	push   %rbx
> > ffffffff8110f579:	48 83 ec 28          	sub    $0x28,%rsp  
> 
> stack offset is 0x28 bytes [*]

Actually, isn't it really 0x40 bytes? The stack pushed 3 words (8 bytes
each) before doing the subtract. 0x28 == 40 bytes, 3 * 8 = 24,
40 + 24 = 64 == 0x40.

> 
> > ffffffff8110f57d:	48 89 fb             	mov    %rdi,%rbx
> > ffffffff8110f580:	e8 6b 6e 80 00       	callq  ffffffff819163f0 <mcount>
> > ffffffff8110f585:	e8 66 6e 80 00       	callq  ffffffff819163f0 <mcount>
> > ffffffff8110f58a:	e8 61 6e 80 00       	callq  ffffffff819163f0 <mcount>
> > ffffffff8110f58f:	e8 5c 6e 80 00       	callq  ffffffff819163f0 <mcount>  
> 
> Your compiler is on drugs!

Totally agree!


[..]

> 
> > ffffffff8110f5fd:	4c 89 75 d0          	mov    %r14,-0x30(%rbp)
> > ffffffff8110f601:	ff 75 d0             	pushq  -0x30(%rbp)
> > ffffffff8110f604:	9d                   	popfq    
> 
> put r14 into -0x30(rbp) and pushes/pops that, see [*] this is 8 bytes
> over stack ?!

But from rbp, the stack is 0x40 bytes. This may be fine.

-- Steve