Hi,
Please ignore this patch as I missed removing the 'flags' variable.
I will resend the corrected patch soon.
> -----Original Message-----
> From: Bhupesh SHARMA
> Sent: Tuesday, March 13, 2012 2:00 PM
> To: linux-usb@xxxxxxxxxxxxxxx
> Cc: linux-media@xxxxxxxxxxxxxxx; spear-devel; Bhupesh SHARMA
> Subject: [PATCH 1/1] usb: gadget/uvc: Remove non-required locking from
> 'uvc_queue_next_buffer' routine
>
> This patch removes the non-required spinlock acquire/release calls on
> 'queue_irqlock' from 'uvc_queue_next_buffer' routine.
>
> This routine is called from 'video->encode' function (which translates
> to either
> 'uvc_video_encode_bulk' or 'uvc_video_encode_isoc') in 'uvc_video.c'.
> As, the 'video->encode' routines are called with 'queue_irqlock'
> already held,
> so acquiring a 'queue_irqlock' again in 'uvc_queue_next_buffer' routine
> causes
> a spin lock recursion.
>
> A sample kernel crash log is given below (as observed on using
> 'g_webcam'
> with DWC designware 2.0 UDC):
>
> Kernel crash log:
> -----------------
> BUG: spinlock recursion on CPU#0, swapper/0/0
> lock: 8f824f70, .magic: dead4ead, .owner: swapper/0/0, .owner_cpu: 0
> Backtrace:
> [<80011b04>] (dump_backtrace+0x0/0x10c) from [<8040bc04>]
> (dump_stack+0x18/0x1c)
> r6:8f8240b4 r5:8f824f70 r4:805a1b80 r3:805b9d00
> [<8040bbec>] (dump_stack+0x0/0x1c) from [<8040e178>]
> (spin_dump+0x80/0x94)
> [<8040e0f8>] (spin_dump+0x0/0x94) from [<8040e1b8>]
> (spin_bug+0x2c/0x30)
> r5:804e88f4 r4:8f824f70
> [<8040e18c>] (spin_bug+0x0/0x30) from [<8019e45c>]
> (do_raw_spin_lock+0x148/0x16c)
> r5:80586000 r4:8f824f70
> [<8019e314>] (do_raw_spin_lock+0x0/0x16c) from [<80411e5c>]
> (_raw_spin_lock_irqsave+0x18/0x20)
> r9:8f81515c r8:8fb30740 r7:8f824f70 r6:8f8240b4 r5:8f8240d0
> r4:60000193
> [<80411e44>] (_raw_spin_lock_irqsave+0x0/0x20) from [<802d17e0>]
> (uvc_queue_next_buffer.part.11+0x2
> 4/0xa4)
> r4:8f824054 r3:00000000
> [<802d17bc>] (uvc_queue_next_buffer.part.11+0x0/0xa4) from [<802d1968>]
> (uvc_video_encode_isoc+0x10
> 8/0x118)
> r7:00000110 r6:00070800 r5:8f8240d0 r4:8f824054
> [<802d1860>] (uvc_video_encode_isoc+0x0/0x118) from [<802cffb8>]
> (uvc_video_complete+0x6c/0x134)
> r8:60000193 r7:8f815120 r6:8f824f70 r5:8f824054 r4:8fb30740
> r3:802d1860
> [<802cff4c>] (uvc_video_complete+0x0/0x134) from [<802cc18c>]
> (req_done+0xd0/0xf4)
> r8:90810400 r7:805dbcd0 r6:00000000 r5:8f815120 r4:8fb30740
> r3:802cff4c
> [<802cc0bc>] (req_done+0x0/0xf4) from [<802cda84>]
> (udc_handle_epn_in_int+0xc0/0x1b8)
> r7:00000400 r6:8059efd4 r5:90810060 r4:8f815120
> [<802cd9c4>] (udc_handle_epn_in_int+0x0/0x1b8) from [<802ce950>]
> (dw_udc_irq+0x10c/0x61c)
> [<802ce844>] (dw_udc_irq+0x0/0x61c) from [<8006951c>]
> (handle_irq_event_percpu+0x54/0x188)
> [<800694c8>] (handle_irq_event_percpu+0x0/0x188) from [<80069694>]
> (handle_irq_event+0x44/0x64)
> [<80069650>] (handle_irq_event+0x0/0x64) from [<8006c270>]
> (handle_fasteoi_irq+0xa0/0x148)
> r6:80586000 r5:8058c894 r4:8058c840 r3:00000000
> [<8006c1d0>] (handle_fasteoi_irq+0x0/0x148) from [<80068d28>]
> (generic_handle_irq+0x34/0x48)
> r5:80584b6c r4:8059f8b8
> [<80068cf4>] (generic_handle_irq+0x0/0x48) from [<8000efa8>]
> (handle_IRQ+0x54/0xb4)
> [<8000ef54>] (handle_IRQ+0x0/0xb4) from [<8000849c>]
> (gic_handle_irq+0x2c/0xb0)
> r8:8059eff8 r7:80587f38 r6:fec80100 r5:8059eff8 r4:00000000
> r3:0000005e
> [<80008470>] (gic_handle_irq+0x0/0xb0) from [<8000dd80>]
> (__irq_svc+0x40/0x60)
> Exception stack(0x80587f38 to 0x80587f80)
> 7f20: ffffffed
> 00000000
> 7f40: 80587f80 00000000 80586000 805f1988 80413864 805a2bb8 80586000
> 411fc091
> 7f60: 00000000 80587f8c 80587f90 80587f80 8000f2a4 8000f2a8 60000013
> ffffffff
> r8:80586000 r7:80587f6c r6:ffffffff r5:60000013 r4:8000f2a8
> r3:8000f2a4
> [<8000f27c>] (default_idle+0x0/0x30) from [<8000f52c>]
> (cpu_idle+0xd8/0xf4)
> [<8000f454>] (cpu_idle+0x0/0xf4) from [<803fd0e0>]
> (rest_init+0x64/0x7c)
> r8:0000406a r7:805a2bac r6:809778c0 r5:8057b144 r4:8059f690
> r3:00000000
> [<803fd07c>] (rest_init+0x0/0x7c) from [<805527ec>]
> (start_kernel+0x294/0x2e8)
> [<80552558>] (start_kernel+0x0/0x2e8) from [<00008044>] (0x8044)
>
> Signed-off-by: Bhupesh Sharma <bhupesh.sharma@xxxxxx>
> ---
> drivers/usb/gadget/uvc_queue.c | 3 +--
> 1 files changed, 1 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/usb/gadget/uvc_queue.c
> b/drivers/usb/gadget/uvc_queue.c
> index d776adb..7ef5efb 100644
> --- a/drivers/usb/gadget/uvc_queue.c
> +++ b/drivers/usb/gadget/uvc_queue.c
> @@ -543,6 +543,7 @@ done:
> return ret;
> }
>
> +/* called with &queue_irqlock held.. */
> static struct uvc_buffer *
> uvc_queue_next_buffer(struct uvc_video_queue *queue, struct uvc_buffer
> *buf)
> {
> @@ -556,14 +557,12 @@ uvc_queue_next_buffer(struct uvc_video_queue
> *queue, struct uvc_buffer *buf)
> return buf;
> }
>
> - spin_lock_irqsave(&queue->irqlock, flags);
> list_del(&buf->queue);
> if (!list_empty(&queue->irqqueue))
> nextbuf = list_first_entry(&queue->irqqueue, struct
> uvc_buffer,
> queue);
> else
> nextbuf = NULL;
> - spin_unlock_irqrestore(&queue->irqlock, flags);
>
> buf->buf.sequence = queue->sequence++;
> do_gettimeofday(&buf->buf.timestamp);
> --
Regards,
Bhupesh
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