Subject: [PATCH v2 1/2] serial: fsl_lpuart: delete timer on shutdown

From: [email-masked] (Stefan Agner)
Date: Sat, 10 Jan 2015 09:09:59 +0100

On 2015-01-10 01:48, Greg KH wrote:
> On Sat, Jan 10, 2015 at 01:08:58AM +0100, Stefan Agner wrote:
>> If the serial port gets closed while a RX transfer is in progress,
>> the timer might fire after the serial port shutdown finished. This
>> leads in a NULL pointer dereference:
>>
>> [    7.508324] Unable to handle kernel NULL pointer dereference at virtual address 00000000
>> [    7.516590] pgd = 86348000
>> [    7.519445] [00000000] *pgd=86179831, *pte=00000000, *ppte=00000000
>> [    7.526145] Internal error: Oops: 17 [#1] ARM
>> [    7.530611] Modules linked in:
>> [    7.533876] CPU: 0 PID: 123 Comm: systemd Not tainted 3.19.0-rc3-00004-g5b11ea7 #1778
>> [    7.541827] Hardware name: Freescale Vybrid VF610 (Device Tree)
>> [    7.547862] task: 861c3400 ti: 86ac8000 task.ti: 86ac8000
>> [    7.553392] PC is at lpuart_timer_func+0x24/0xf8
>> [    7.558127] LR is at lpuart_timer_func+0x20/0xf8
>> [    7.562857] pc : [<802df99c>]    lr : [<802df998>]    psr: 600b0113
>> [    7.562857] sp : 86ac9b90  ip : 86ac9b90  fp : 86ac9bbc
>> [    7.574467] r10: 80817180  r9 : 80817b98  r8 : 80817998
>> [    7.579803] r7 : 807acee0  r6 : 86989000  r5 : 00000100  r4 : 86997210
>> [    7.586444] r3 : 86ac8000  r2 : 86ac9bc0  r1 : 86997210  r0 : 00000000
>> [    7.593085] Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment user
>> [    7.600341] Control: 10c5387d  Table: 86348059  DAC: 00000015
>> [    7.606203] Process systemd (pid: 123, stack limit = 0x86ac8230)
>>
>> Setup the timer on UART startup which allows to delete the timer
>> unconditionally on shutdown. This also saves the initialization
>> on each transfer.
>>
>> Signed-off-by: Stefan Agner <[email-masked]>
>> ---
>>  drivers/tty/serial/fsl_lpuart.c | 7 ++++---
>>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> Do stable kernels care about this as well, or is this just a regression
> from 3.18?

This is an issue since DMA support for lpuart was included in the
kernel, which was in 3.14.

--
Stefan