[BUG] atmel: spi: scheduling while atomic

[Yang, Wenyou]

> -----Original Message-----
> From: Jiří Prchal [mailto:jiri.prchal at aksignal.cz]
> Sent: Monday, March 10, 2014 4:12 PM
> To: Rabin Vincent; Alexandre Belloni; Yang, Wenyou
> Cc: Ferre, Nicolas; linux-arm-kernel at lists.infradead.org;
> sboyd at codeaurora.org
> Subject: Re: [BUG] atmel: spi: scheduling while atomic
> 
> Hi all,
> at first: warning is on all spi devices.
> at second: its with CONFIG_PREEMPT=y, without (# CONFIG_PREEMPT_RCU is
> not set) is OK, but I wonder if this config will be fast enough for our
> usage (nearly RT)?
> 
> 
> Dne 8.3.2014 01:41, Rabin Vincent napsal(a):
> > 2014-03-07 23:58 GMT+01:00 Alexandre Belloni
> > <alexandre.belloni at free-electrons.com>:
> >> On 05/03/2014 at 07:56:04 +0100, Jiří Prchal wrote :
> >>> [    0.902343] BUG: scheduling while atomic: spi0/383/0x00000002
> >>> [    0.906250] Modules linked in:
> >>> [    0.906250] CPU: 0 PID: 383 Comm: spi0 Not tainted 3.14.0-
> rc4_cpm9g25+ #1
> >>> [    0.906250] [<c000d9f4>] (unwind_backtrace) from [<c000bdc0>]
> (show_stack+0x10/0x14)
> >>> [    0.906250] [<c000bdc0>] (show_stack) from [<c003a224>]
> (__schedule_bug+0x48/0x60)
> >>> [    0.906250] [<c003a224>] (__schedule_bug) from [<c0390294>]
> (__schedule+0x60/0x484)
> >>> [    0.906250] [<c0390294>] (__schedule) from [<c038feac>]
> (schedule_timeout+0x17c/0x1ac)
> >>> [    0.906250] [<c038feac>] (schedule_timeout) from [<c039111c>]
> (wait_for_common+0x10c/0x1f0)
> >>> [    0.906250] [<c039111c>] (wait_for_common) from [<c0249228>]
> (atmel_spi_transfer_one_message+0x71c/0xa48)
> >>> [    0.906250] [<c0249228>] (atmel_spi_transfer_one_message) from
> [<c0246624>] (spi_pump_messages+0x210/0x238)
> >>> [    0.906250] [<c0246624>] (spi_pump_messages) from [<c00343d0>]
> (kthread_worker_fn+0x15c/0x1b4)
> >>> [    0.906250] [<c00343d0>] (kthread_worker_fn) from [<c0034534>]
> (kthread+0xb8/0xcc)
> >>> [    0.906250] [<c0034534>] (kthread) from [<c0009510>]
> (ret_from_fork+0x14/0x24)
> >>> [    0.906250] at25 spi0.0: 128 KByte at25 eeprom, pagesize 512
> >>
> >> Actually, I'm not quite sure how spi_pump_messages can be called from
> an
> >> atomic context.
> >
> > spi_pump_messages() is not called from atomic context.  Rather,
> > atmel_spi_transfer_one_message() does a spin_lock_irqsave() (via
> > atmel_spi_lock()) and then calls atmel_spi_one_transfer(), which calls
> > wait_for_completion_timeout().  That's why schedule is being called
> > from atomic context.  This was introduced by 8090d6d1a4 ("spi: atmel:
> > Refactor spi-atmel to use SPI framework queue"). I think you should
> > see the warning with CONFIG_PREEMPT=y.
> >

Thanks a lot for the report and analysis.

--->8-------- 
From ba2dd7aee12cb09b9ef159251859443e1b055669 Mon Sep 17 00:00:00 2001
From: Wenyou Yang <wenyou.yang at atmel.com>
Date: Mon, 10 Mar 2014 16:44:33 +0800
Subject: [PATCH] spi: atmel: fix BUG: scheduling while atomic with
 CONFIG_PREEMPT=y

introduced by 8090d6d1a415d3ae1a7208995decfab8f60f4f36
("spi: atmel: Refactor spi-atmel to use SPI framework queue")

Signed-off-by: Wenyou Yang <wenyou.yang at atmel.com>
---
 drivers/spi/spi-atmel.c |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/spi/spi-atmel.c b/drivers/spi/spi-atmel.c
index b0842f7..e05c3f2 100644
--- a/drivers/spi/spi-atmel.c
+++ b/drivers/spi/spi-atmel.c
@@ -1130,8 +1130,12 @@ static int atmel_spi_one_transfer(struct spi_master *master,
 			atmel_spi_next_xfer_pio(master, xfer);
 		}
 
+		atmel_spi_unlock(as);
+
 		ret = wait_for_completion_timeout(&as->xfer_completion,
 							SPI_DMA_TIMEOUT);
+		atmel_spi_lock(as);
+
 		if (WARN_ON(ret == 0)) {
 			dev_err(&spi->dev,
 				"spi trasfer timeout, err %d\n", ret);
-- 
1.7.9.5
---<8----

This patch should fix this issue.
I know it is not good one, the lock usage in the driver code should be double checked.

Thanks.

Best Regards,
Wenyou Yang.