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Message-ID: <4AB4A25C.9000904@gmail.com>
Date: Sat, 19 Sep 2009 11:20:28 +0200
From: Jiri Slaby <jirislaby@gmail.com>
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To: Krzysztof Helt <krzysztof.h1@wp.pl>
CC: linux-input@vger.kernel.org,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: hid-core: fix lockdep in hid_input_report()
References: <20090919081549.669b6773.krzysztof.h1@wp.pl>
In-Reply-To: <20090919081549.669b6773.krzysztof.h1@wp.pl>
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On 09/19/2009 08:15 AM, Krzysztof Helt wrote:
> There is a lockdep warning in the hid_input_report() due to dynamic allocation
> of a temporary buffer.
> Change the buffer to a local variable. The buffer size is 512 chars.

I personally don't like this approach. Adding 0.5k to a stack is not a
good idea (and it is worse when one looks at the long trace). I think
hid_ctrl should call hid_input_report with 1 as the last argument instead.

> The lockdep trace is:
> 
> WARNING: at kernel/lockdep.c:2457 lockdep_trace_alloc+0xca/0xd0()
> Hardware name: Product Name
> Modules linked in: usbhid(+) hid uhci_hcd ne2k_pci via_agp 8390 i2c_via
> Pid: 0, comm: swapper Not tainted 2.6.31 #74
> Call Trace:
>  [<c0243b8a>] ? lockdep_trace_alloc+0xca/0xd0
>  [<c0221d1c>] warn_slowpath_common+0x7c/0xa0
>  [<c0243b8a>] ? lockdep_trace_alloc+0xca/0xd0
>  [<c0221d55>] warn_slowpath_null+0x15/0x20
>  [<c0243b8a>] lockdep_trace_alloc+0xca/0xd0
>  [<c027d2c8>] kmem_cache_alloc+0x28/0x100
>  [<cc9359ef>] ? hid_input_report+0x6f/0x220 [hid]
>  [<cc9359ef>] hid_input_report+0x6f/0x220 [hid]
>  [<cc94cabf>] hid_ctrl+0x7f/0x180 [usbhid]
>  [<c03b28b1>] usb_hcd_giveback_urb+0x41/0xa0
>  [<cc91a3fc>] uhci_giveback_urb+0x8c/0x280 [uhci_hcd]
>  [<c0279853>] ? dma_pool_free+0xd3/0x120
>  [<cc919848>] ? uhci_free_td+0x58/0xa0 [uhci_hcd]
>  [<cc91ac01>] uhci_scan_schedule+0x301/0x910 [uhci_hcd]
>  [<cc91cac4>] uhci_irq+0x94/0x940 [uhci_hcd]
>  [<c0245c43>] ? __lock_acquire+0x433/0xab0
>  [<c0206246>] ? mask_and_ack_8259A+0x66/0x100
>  [<c03b494b>] usb_hcd_irq+0x6b/0x90
>  [<c0255e7d>] handle_IRQ_event+0x2d/0xc0
>  [<c0257e85>] handle_level_irq+0x65/0xe0
>  [<c0204c74>] handle_irq+0x34/0x60
>  [<c0204bc9>] do_IRQ+0x39/0xb0
>  [<c024365c>] ? trace_hardirqs_on_caller+0x12c/0x180
>  [<c020328e>] common_interrupt+0x2e/0x40
>  [<c0208d48>] ? default_idle+0x38/0x50
>  [<c02108df>] apm_cpu_idle+0x10f/0x290
>  [<c0201b11>] cpu_idle+0x21/0x40
>  [<c045892d>] rest_init+0x4d/0x60
>  [<c0575815>] start_kernel+0x235/0x280
>  [<c05751f0>] ? unknown_bootoption+0x0/0x210
>  [<c057503f>] __init_begin+0x3f/0x50