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Date: Tue, 1 Mar 2016 10:59:57 -0500 (EST)
From: Alan Stern <stern@rowland.harvard.edu>
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To: Sedat Dilek <sedat.dilek@gmail.com>
cc: Steven Rostedt <rostedt@goodmis.org>, Jiri Kosina <jikos@kernel.org>,
        Tejun Heo <tj@kernel.org>, Lai Jiangshan <jiangshanlai@gmail.com>,
        Benjamin Tissoires <benjamin.tissoires@redhat.com>,
        Paul McKenney <paulmck@linux.vnet.ibm.com>,
        Andy Lutomirski <luto@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
        <linux-usb@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Felipe Balbi <balbi@ti.com>, Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>
Subject: Re: [PATCH] usbhid: Fix lockdep unannotated irqs-off warning
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On Tue, 1 Mar 2016, Sedat Dilek wrote:

> On Tue, Oct 13, 2015 at 2:57 AM, Steven Rostedt <rostedt@goodmis.org> wrote:
> > On Sat, 3 Oct 2015 12:05:42 +0200
> > Sedat Dilek <sedat.dilek@gmail.com> wrote:
> >
> >> So, at the beginning... dunno WTF is causing the problems - no
> >> workaround for CLANG.
> >
> > Probably need to compile with gcc and with clang and look at the binary
> > differences. Or at least what objdump shows.
> >
> 
> [ Hope to address this issue to the correct people - CCed some people
> I taped on their nerves ]
> 
> Not sure if I should open a new thread?
> Please, some clear statements on this.
> Thanks.
> 
> The issue is still visible and alive.

...

> [ FACT #3: TEST-CASE #2 ]
> 
> The most reliable test-case is to simply unplug my external Logitech
> USB mouse - saw this by accident.
> YES, it was so simple.
> 
> --- dmesg_4.5.0-rc6-2-llvmlinux-amd64.txt       2016-02-29
> 21:23:56.399691975 +0100
> +++ dmesg_4.5.0-rc6-2-llvmlinux-amd64_usbmouse-unplugged.txt
> 2016-02-29 21:28:14.401832240 +0100
> @@ -832,3 +832,75 @@
>  [   66.529779] PPP BSD Compression module registered
>  [   66.563013] PPP Deflate Compression module registered
>  [   66.978977] usb 2-1.5: USB disconnect, device number 4
> +[  321.937369] usb 2-1.4: USB disconnect, device number 3
> +[  321.950810] BUG: sleeping function called from invalid context at
> kernel/workqueue.c:2785
> +[  321.950816] in_atomic(): 0, irqs_disabled(): 1, pid: 44, name: kworker/2:1

> +[  321.950885] hardirqs last  enabled at (47769):
> [<ffffffff819426a2>] _raw_spin_unlock_irq+0x32/0x60
> +[  321.950889] hardirqs last disabled at (47770):
> [<ffffffff81115bdc>] del_timer_sync+0x3c/0x110
> +[  321.950894] softirqs last  enabled at (47112):
> [<ffffffff810871a2>] __do_softirq+0x5a2/0x610
> +[  321.950898] softirqs last disabled at (47097):
> [<ffffffff8108747c>] irq_exit+0x9c/0x120
> +[  321.950903] CPU: 2 PID: 44 Comm: kworker/2:1 Not tainted
> 4.5.0-rc6-2-llvmlinux-amd64 #1
> +[  321.950905] Hardware name: SAMSUNG ELECTRONICS CO., LTD.
> 530U3BI/530U4BI/530U4BH/530U3BI/530U4BI/530U4BH, BIOS 13XK 03/28/2013
> +[  321.950908] Workqueue: usb_hub_wq hub_event
> +[  321.950911]  ffff8800d3326948 0000000000000092 0000000000000000
> ffff8800d4347568
> +[  321.950915]  ffffffff814ba7d4 ffff8800d43474f8 ffff8800d4340cc0
> ffff8800d4347568
> +[  321.950919]  ffffffff810e28fd 0000000000000092 0000000000000096
> ffff8800d43475a8
> +[  321.950923] Call Trace:
> +[  321.950927]  [<ffffffff814ba7d4>] dump_stack+0xa4/0xf0
> +[  321.950931]  [<ffffffff810e28fd>] ? print_irqtrace_events+0xcd/0xe0
> +[  321.950936]  [<ffffffff810bf495>] ___might_sleep+0x295/0x2b0
> +[  321.950939]  [<ffffffff810bf18f>] __might_sleep+0x4f/0xc0
> +[  321.950943]  [<ffffffff810a12ef>] start_flush_work+0x2f/0x2a0
> +[  321.950946]  [<ffffffff810a129c>] flush_work+0x5c/0x80
> +[  321.950949]  [<ffffffff810a125a>] ? flush_work+0x1a/0x80
> +[  321.950953]  [<ffffffff810e247d>] ? trace_hardirqs_off+0xd/0x10
> +[  321.950956]  [<ffffffff810a032a>] ? try_to_grab_pending+0x4a/0x260
> +[  321.950960]  [<ffffffff810a1717>] __cancel_work_timer+0x197/0x290
> +[  321.950963]  [<ffffffff81115b8d>] ? try_to_del_timer_sync+0xad/0xc0
> +[  321.950966]  [<ffffffff810a1578>] cancel_work_sync+0x18/0x20

It's possible that this could be a compiler-related error connected 
with local_irq_save().  __cancel_work_timer() calls 

		ret = try_to_grab_pending(work, is_dwork, &flags);

and try_to_grab_pending() starts this way:

static int try_to_grab_pending(struct work_struct *work, bool is_dwork,
			       unsigned long *flags)
{
	struct worker_pool *pool;
	struct pool_workqueue *pwq;

	local_irq_save(*flags);

Then later on, __cancel_work_timer() does

	local_irq_restore(flags);

Maybe CLANG doesn't like local_irq_save() applied to a pointer as 
opposed to a stack variable.

As a quick test, try applying the patch below.  (Note that there is a 
similar construction in kernel/signal.c.)

Alan Stern



Index: usb-4.4/kernel/workqueue.c
===================================================================
--- usb-4.4.orig/kernel/workqueue.c
+++ usb-4.4/kernel/workqueue.c
@@ -1175,12 +1175,14 @@ out_put:
  * This function is safe to call from any context including IRQ handler.
  */
 static int try_to_grab_pending(struct work_struct *work, bool is_dwork,
-			       unsigned long *flags)
+			       unsigned long *pflags)
 {
 	struct worker_pool *pool;
 	struct pool_workqueue *pwq;
+	unsigned long flags;
 
-	local_irq_save(*flags);
+	local_irq_save(flags);
+	*pflags = flags;
 
 	/* try to steal the timer if it exists */
 	if (is_dwork) {
@@ -1241,7 +1243,7 @@ static int try_to_grab_pending(struct wo
 	}
 	spin_unlock(&pool->lock);
 fail:
-	local_irq_restore(*flags);
+	local_irq_restore(flags);
 	if (work_is_canceling(work))
 		return -ENOENT;
 	cpu_relax();