On Thu, Dec 15, 2011 at 12:04:42PM +0100, Claudio Scordino wrote:

Il 15/12/2011 11:00, Nicolas Ferre ha scritto:

quoted

On 12/15/2011 09:47 AM, Claudio Scordino :

quoted

Hi all.

We have encountered a spinlock lockup in the RS485 part of the
atmel_serial driver.

Here is the trace:

[   68.030000] BUG: spinlock lockup on CPU#0, dnp_master/244, c07e82c0
[   68.040000] [<c002a790>] (unwind_backtrace+0x0/0xf0) from
[<c012f8f0>] (do_raw_spin_lock+0x10c/0x148)
[   68.050000] [<c012f8f0>] (do_raw_spin_lock+0x10c/0x148) from
[<c015152c>] (atmel_tasklet_func+0x10/0x708)
[   68.060000] [<c015152c>] (atmel_tasklet_func+0x10/0x708) from
[<c003bfd4>] (tasklet_action+0x8c/0xf4)
[   68.070000] [<c003bfd4>] (tasklet_action+0x8c/0xf4) from [<c003c630>]
(__do_softirq+0xa4/0x180)
[   68.080000] [<c003c630>] (__do_softirq+0xa4/0x180) from [<c003c764>]
(irq_exit+0x58/0xb0)
[   68.090000] [<c003c764>] (irq_exit+0x58/0xb0) from [<c0021084>]
(asm_do_IRQ+0x84/0xa4)
[   68.100000] [<c0021084>] (asm_do_IRQ+0x84/0xa4) from [<c002622c>]
(__irq_svc+0x4c/0x98)
[   68.110000] Exception stack(0xc341fdc8 to 0xc341fe10)
[   68.110000] fdc0:                   c07e82c0 00000000 00000200
c4818000 c341fe10 c07e82c0
[   68.120000] fde0: 00000000 c07e82c0 c38d3318 c341e000 bebcee00
010a0b60 c07e83fc c341fe10
[   68.130000] fe00: c0151d54 c023d9c0 60000013 ffffffff
[   68.140000] [<c002622c>] (__irq_svc+0x4c/0x98) from [<c023d9c0>]
(_raw_spin_unlock+0x0/0x48)
[   68.140000] [<c023d9c0>] (_raw_spin_unlock+0x0/0x48) from
[<00000000>] (  (null))

The soft lockup occurs later

[  126.750000] BUG: soft lockup - CPU#0 stuck for 61s! [dnp_master:244]
[  126.750000] irq event stamp: 0
[  126.750000] hardirqs last  enabled at (0): [<   (null)>]   (null)
[  126.750000] hardirqs last disabled at (0): [<c0035e30>]
copy_process+0x308/0xe78
[  126.750000] softirqs last  enabled at (0): [<c0035e30>]
copy_process+0x308/0xe78
[  126.750000] softirqs last disabled at (0): [<   (null)>]   (null)


The following patch (already tested by Dave, who also reported the bug)
fixes the problem.

Regards,

    Claudio




Subject: atmel_serial: fix spinlock lockup in RS485 code

Patch to fix a spinlock lockup in the driver that sometimes happens when
the
tasklet starts.

Signed-off-by: Claudio Scordino<redacted>
Signed-off-by: Dave Bender<redacted>
Tested-by: Dave Bender<redacted>

Acked-by: Nicolas Ferre<redacted>

Claudio, can you please send the patch to Alan with my "Acked-by" and an
addition to Linux stable just after the signature lines:

Cc: stable<stable@kernel.org>

That address has been invalid since August, please use
stable@vger.kernel.org now.

Dear Alan,

	here is the patch with all the acked-bys.

I'll take care of this.

thanks,

greg k-h