Date:   Tue, 7 Mar 2017 13:46:10 +0100
From:   Tobias Klauser <tklauser@...tanz.ch>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Sven Schmidt <4sschmid@...ormatik.uni-hamburg.de>,
        Sandra Loosemore <sandra@...esourcery.com>,
        Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Ley Foon Tan <lftan@...era.com>,
        nios2-dev@...ts.rocketboards.org
Subject: Re: nios2 crash/hang in mainline due to 'lib: update LZ4 compressor
 module'

On 2017-03-03 at 04:04:41 +0100, Guenter Roeck <linux@...ck-us.net> wrote:
> On 03/02/2017 08:38 AM, Tobias Klauser wrote:
> >On 2017-03-01 at 20:45:21 +0100, Guenter Roeck <linux@...ck-us.net> wrote:
> >>On Wed, Mar 01, 2017 at 07:58:17PM +0100, Sven Schmidt wrote:
> >>>Hi Guenter, Tobias and Sandra,
> >>>
> >>>thanks for your effort here.
> >>>
> >>>On Tue, Feb 28, 2017 at 10:14:13AM -0800, Guenter Roeck wrote:
> >>>>On Tue, Feb 28, 2017 at 10:53:56AM -0700, Sandra Loosemore wrote:
> >>>>>On 02/28/2017 08:53 AM, Tobias Klauser wrote:
> >>>>>>(adding Sandra Loosemore to Cc due to possible relation to gcc/binutils
> >>>>>>for nios2)
> >>>>>>
> >>>>>>On 2017-02-26 at 22:03:38 +0100, Guenter Roeck <linux@...ck-us.net> wrote:
> >>>>>>>Hi Sven,
> >>>>>>>
> >>>>>>>my qemu test for nios2 started failing with commit 4e1a33b105dd ("lib:
> >>>>>>>update LZ4 compressor module"). The test hangs early during boot before
> >>>>>>>any console output is seen. Reverting the offending patch as well as the
> >>>>>>>subsequent lz4 related patches fixes the problem. Disabling CONFIG_RD_LZ4
> >>>>>>>and with it other LZ4 options also fixes it (as does adding "return -EINVAL;"
> >>>>>>>at the top of the LZ4 decompression code). For reference, bisect log
> >>>>>>>is attached.
> >>>>>>>
> >>>>>>>I tried with buildroot toolchains using gcc 6.1.0 as well as 6.3.0
> >>>>>>>and binutils 2.26.1. Scripts used to run the tests are available at
> >>>>>>>https://github.com/groeck/linux-build-test/tree/master/rootfs/nios2.
> >>>>>>>Qemu is from qemu mainline or qemu v2.8 with nios2 patches applied.
> >>>>>>
> >>>>>>Looks like this is somehow related to gcc/binutils. Using GCC 4.8.3 and
> >>>>>>binutils 2.24.51 (both from from Sourcery CodeBench Lite 2014.05) I can
> >>>>>>get a kernel booting on latest master branch. AFAICT, none of the
> >>>>>>LZ4_decompress_* functions are called during boot.
> >>>>>>
> >>>
> >>>It seems a bit strange that code which is not actually called causes problems like that.
> >>>
> >>Yes, it is, though it is always possible. The code isn't exactly easy to
> >>understand; there may be some hidden caveats such as global variables. It may
> >>also be that some jump target exceeds its range (though why that would only
> >>be seen with the LZ4 code is another question), or that the compiler gets
> >>confused by the forced inlines (disabling that didn't make a difference,
> >>though, nor did disabling -O3).
> >>
> >>>Please let me know if and how I may help you figure out what's happening, especially
> >>>regarding the differences between the previous LZ4 and the current implementation.
> >>>
> >>
> >>For my part I am all but clueless. Unless someone has an idea, we may to
> >>disable LZ4 support for nios2 for the time being. Does anyone have thoughts
> >>on that ? Of course, that would not help if the problem also affects
> >>recent gcc/binutil versions on other architectures.
> >
> >After some further investigations, I'd say this isn't "caused" by LZ4
> >specifically but by a more general problem with one of the nios2 arch
> >specific tools involved.
> >
> >I manually enabled random additional CONFIG_* options and in some cases
> >I got the kernel to boot (with CONFIG_RD_LZ4 enabled and no return
> >-EINVAL in place) while in others I didn't. So I'd rather suspect this
> >problem to be connected to the size or structure of the generated vmlinux
> >image.
> >
> >Or could this even be a problem with qemu? Did anyone already verify
> >this on the 10m50 devboard? (Unfortunately I don't have any nios2
> >devboard available right now, otherwise I would have done this...)
> >
> 
> That is of course always possible.
> 
> >Other than that I'm also becoming all but clueless... One option I
> >thought of was using the QEMU monitor to dump the CPU state after the
> >hang but so far I didn't manage to get it to work (hints appreciated ;)
> >
> 
> Something like
> 
> qemu-system-nios2 -M 10m50-ghrd -kernel vmlinux -no-reboot \
> 	-dtb arch/nios2/boot/dts/10m50_devboard.dtb \
> 	--append "rdinit=/sbin/init" -initrd busybox-nios2.cpio
> 
> gives you a qemu monitor window. Use "info registers" to see registers.
> Looks like it is stuck in init_bootmem_core, or at least that is what it
> shows for me.

Thanks a lot for the hint, this worked perfectly. I'm not all that
familiar with qemu :-/

Using the qemu gdbserver I can indeed confirm that it seems to be stuck
in init_bootmem_core:

(gdb) file vmlinux
Reading symbols from vmlinux...done.
(gdb) target remote localhost:1234
Remote debugging using localhost:1234
link_bootmem (bdata=<optimized out>) at mm/bootmem.c:80
80			if (bdata->node_min_pfn < ent->node_min_pfn) {

This looks like a very weird place for it to get stuck...

So I followed a different path and implemented early printk support for
the 8250/16650 serial console on nios2, so I could get debug outputs
earlier on (patch below, I'll also officially submit this later one).

Now I get the following output on boot:

Linux version 4.11.0-rc1-dirty (tobiask@...s08) (gcc version 7.0.1 20170226 (experimental) (GCC) ) #46 Tue Mar 7 13:40:53 CET 2017
bootconsole [early0] enabled
Early console on uart16650 initialized at 0xf8001600
OF: fdt: Error -11 processing FDT
Kernel panic - not syncing: setup_cpuinfo: No CPU found in devicetree!

---[ end Kernel panic - not syncing: setup_cpuinfo: No CPU found in devicetree!

Looks like the in-memory device tree somehow gets corrupted. Not sure
yet why and how this is linked to the Kconfig options selected but at
least we now have a possibility to use debug messages earlier on.

---%<---%<---

Patch for 8250/16650 early printk support on nios2 (make sure to select
CONFIG_EARLY_PRINTK):

diff --git a/arch/nios2/Kconfig.debug b/arch/nios2/Kconfig.debug
index 2fd08cbfdddb..35b5dd67b15a 100644
--- a/arch/nios2/Kconfig.debug
+++ b/arch/nios2/Kconfig.debug
@@ -18,7 +18,7 @@ config EARLY_PRINTK
 	bool "Activate early kernel debugging"
 	default y
 	select SERIAL_CORE_CONSOLE
-	depends on SERIAL_ALTERA_JTAGUART_CONSOLE || SERIAL_ALTERA_UART_CONSOLE
+	depends on SERIAL_ALTERA_JTAGUART_CONSOLE || SERIAL_ALTERA_UART_CONSOLE || SERIAL_8250_CONSOLE
 	help
 	  Enable early printk on console
 	  This is useful for kernel debugging when your machine crashes very
diff --git a/arch/nios2/kernel/early_printk.c b/arch/nios2/kernel/early_printk.c
index c08e4c1486fc..24b4506f4969 100644
--- a/arch/nios2/kernel/early_printk.c
+++ b/arch/nios2/kernel/early_printk.c
@@ -22,6 +22,8 @@ static unsigned long base_addr;
 
 #if defined(CONFIG_SERIAL_ALTERA_JTAGUART_CONSOLE)
 
+#define UART_NAME "altera_jtaguart"
+
 #define ALTERA_JTAGUART_DATA_REG		0
 #define ALTERA_JTAGUART_CONTROL_REG		4
 #define ALTERA_JTAGUART_CONTROL_WSPACE_MSK	0xFFFF0000
@@ -53,6 +55,8 @@ static void early_console_write(struct console *con, const char *s, unsigned n)
 
 #elif defined(CONFIG_SERIAL_ALTERA_UART_CONSOLE)
 
+#define UART_NAME "altera_uart"
+
 #define ALTERA_UART_TXDATA_REG		4
 #define ALTERA_UART_STATUS_REG		8
 #define ALTERA_UART_STATUS_TRDY		0x0040
@@ -80,9 +84,40 @@ static void early_console_write(struct console *con, const char *s, unsigned n)
 	}
 }
 
+#elif defined(CONFIG_SERIAL_8250_CONSOLE)
+
+#define UART_NAME "uart16650"
+
+#define UART_LSR_TEMT	0x40 /* Transmitter empty */
+#define UART_LSR_THRE	0x20 /* Transmit-hold-register empty */
+#define BOTH_EMPTY (UART_LSR_TEMT | UART_LSR_THRE)
+
+#define UART_GET_SR() \
+	__builtin_ldwio((void *)(base_addr + 0x14))
+#define UART_SET_TX(v) \
+	__builtin_stwio((void *)(base_addr), v)
+
+static void early_console_putc(char c)
+{
+	while (!((UART_GET_SR() & BOTH_EMPTY) == BOTH_EMPTY))
+		;
+
+	UART_SET_TX(c & 0xff);
+}
+
+static void early_console_write(struct console *con, const char *s, unsigned n)
+{
+	while (n-- && *s) {
+		early_console_putc(*s);
+		if (*s == '\n')
+			early_console_putc('\r');
+		s++;
+	}
+}
+
 #else
-# error Neither SERIAL_ALTERA_JTAGUART_CONSOLE nor SERIAL_ALTERA_UART_CONSOLE \
-selected
+# error Neither SERIAL_ALTERA_JTAGUART_CONSOLE, SERIAL_ALTERA_UART_CONSOLE, \
+        nor SERIAL_8250_CONSOLE selected
 #endif
 
 static struct console early_console_prom = {
@@ -95,7 +130,8 @@ static struct console early_console_prom = {
 void __init setup_early_printk(void)
 {
 #if defined(CONFIG_SERIAL_ALTERA_JTAGUART_CONSOLE) ||	\
-	defined(CONFIG_SERIAL_ALTERA_UART_CONSOLE)
+	defined(CONFIG_SERIAL_ALTERA_UART_CONSOLE) ||	\
+	defined(CONFIG_SERIAL_8250_CONSOLE)
 	base_addr = of_early_console();
 #else
 	base_addr = 0;
@@ -114,5 +150,5 @@ void __init setup_early_printk(void)
 
 	early_console = &early_console_prom;
 	register_console(early_console);
-	pr_info("early_console initialized at 0x%08lx\n", base_addr);
+	pr_info("Early console on %s initialized at 0x%08lx\n", UART_NAME, base_addr);
 }

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