Re: Crash in msm serial on dragonboard with ftrace bootargs

[Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>]

On 10/17/2018 4:39 AM, Joel Fernandes wrote:
> On Tue, Oct 16, 2018 at 05:08:25PM +0530, Sai Prakash Ranjan wrote:
>> Hi,
>>
>> On dragonboard 410c, with "ftrace=function" boot args, the console output
>> slows down and board resets without any backtrace as below. This is tested
>> on latest kernel and seems to exist even in older kernels as well.
>>
>> [    2.949164] EINJ: ACPI disabled.
>> [    3.133001] Serial: 8250/16550 dri
>> Format: Log Type - Time(microsec) - Message - Optional Info
>> Log Type: B - Since Boot(Power On Reset),  D - Delta,  S - Statistic
>>
>> But with pstore enabled, able to get the below backtrace:
>> <4>[    2.949164] EINJ: ACPI disabled.
>> <6>[    3.133001] Serial: 8250/16550 driver, 4 ports, IRQ sharing enabled
>> <6>[    3.164097] SuperH (H)SCI(F) driver initialized
>> <0>[    3.164471] Internal error: synchronous external abort: 96000010 [#1]
>> PREEMPT SMP
>> <4>[    3.164479] Modules linked in:
>> <4>[    3.164495] CPU: 2 PID: 1 Comm: swapper/0 Not tainted
>> 4.19.0-rc8-00008-ge033b9909fff-dirty #175
>> <4>[    3.164501] Hardware name: Qualcomm Technologies, Inc. APQ 8016 SBC
>> (DT)
>> <4>[    3.164508] pstate: 40000085 (nZcv daIf -PAN -UAO)
>> <4>[    3.164514] pc : msm_read.isra.2+0x20/0x50
>> <4>[    3.164520] lr : msm_read.isra.2+0x1c/0x50
>> <4>[    3.164526] sp : ffff000008033a50
>> <4>[    3.164531] x29: ffff000008033a50 x28: ffff000009486018
>> <4>[    3.164548] x27: 0000000000000001 x26: ffff7dfffe7ff070
>> <4>[    3.164565] x25: 0000000000000034 x24: ffff000009486000
>> <4>[    3.164582] x23: 0000000000000000 x22: ffff00000978e190
>> <4>[    3.164599] x21: ffff0000095e8228 x20: 0000000000000034
>> <4>[    3.164616] x19: ffff7dfffe7ff008 x18: ffffffffffffffff
>> <4>[    3.164632] x17: 0000000000000000 x16: 0000000000000000
>> <4>[    3.164649] x15: ffff0000094a96c8 x14: ffff00008978e6bf
>> <4>[    3.164666] x13: ffff00000978e6cd x12: 0000000000000038
>> <4>[    3.164683] x11: ffff0000094c6000 x10: 0000000000000c24
>> <4>[    3.164699] x9 : ffff80003c89b400 x8 : ffff000008033970
>> <4>[    3.164716] x7 : ffff80000eb04100 x6 : 00000000000af304
>> <4>[    3.164732] x5 : 0000000000000c40 x4 : ffff80003c06f000
>> <4>[    3.164750] x3 : ffff80003c89b498 x2 : 0000000000000000
>> <4>[    3.164766] x1 : ffff80003ca68000 x0 : 0000000000000800
>> <0>[    3.164785] Process swapper/0 (pid: 1, stack limit =
>> 0x(____ptrval____))
>> <4>[    3.164791] Call trace:
>> <4>[    3.164797]  msm_read.isra.2+0x20/0x50
>> <4>[    3.164804]  msm_reset_dm_count+0x44/0x80
>> <4>[    3.164810]  __msm_console_write+0x1c8/0x1d0
>> <4>[    3.164816]  msm_serial_early_write_dm+0x3c/0x50
>> <4>[    3.164823]  console_unlock.part.6+0x468/0x528
>> <4>[    3.164829]  vprintk_emit+0x210/0x218
>> <4>[    3.164835]  vprintk_default+0x48/0x58
>> <4>[    3.164841]  vprintk_func+0xf0/0x1c0
>> <4>[    3.164847]  printk+0x74/0x94
>> <4>[    3.164853]  sci_init+0x24/0x3c
>> <4>[    3.164859]  do_one_initcall+0x54/0x248
>> <4>[    3.164866]  kernel_init_freeable+0x210/0x378
>> <4>[    3.164872]  kernel_init+0x18/0x118
>> <4>[    3.164878]  ret_from_fork+0x10/0x1c
>> <0>[    3.164884] Code: aa1e03e0 8b214273 97e616f7 d503201f (b9400260)
>>
>> Seems to be issue with the msm serial driver and not ftrace.
>> Could someone look into it.
>>
>> One more thing is for pstore dmesg-ramoops, I had to change late_initcall to
>> postcore_initcall which brings the question as to why we changed to
>> late_initcall?
>> Simple git blame shows to support crypto compress api, but is it really
>> helpful? A lot of boottime issues can be caught with pstore enabled at
>> postcore_initcall rather than late_initcall, this backtrace
>> is just one example. Is there any way we could change this?
> 
> Any chance you are able to dig deeper into the stack trace? I would
> disassemble vmlinux and see which part of msm_read is generating the
> synchronous external abort and look into that.
> 

Yes I had checked the part of msm_read which was generating the abort 
and it always seems to be in "msm_wait_for_xmitr" at below pointed location.

static inline void msm_wait_for_xmitr(struct uart_port *port)
{
         while (!(msm_read(port, UART_SR) & UART_SR_TX_EMPTY)) {     <---
                 if (msm_read(port, UART_ISR) & UART_ISR_TX_READY)
                         break;
                 udelay(1);
         }
         msm_write(port, UART_CR_CMD_RESET_TX_READY, UART_CR);
}

Also I could confirm that this path is entered repeatedly(with tracing 
register reads/writes from my patch series in 
https://lore.kernel.org/patchwork/cover/983795/ and tp_printk) and crash 
is seen at some random time, so could not get much from this.

> Also similar to what Steve suggested, I wonder if it boots for you if you
> annotate all the functions in the serial driver with 'notrace'.
> 

I have tried this too, but still the target crashes. So I am doubtful if 
this is ftrace issue? Maybe earlycon uart issue as Stephen is suspecting.

Thanks,
Sai

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