Subject: [PATCH] n_tty: use kmalloc() instead of vmalloc() to avoid crash on armada-xp

From: [email-masked] (Stas Sergeev)
Date: Tue, 10 Mar 2015 20:51:58 +0300

10.03.2015 20:35, Peter Hurley ?????:
> On 03/10/2015 12:54 PM, Stas Sergeev wrote:
>> Hello, the patch below is needed for a successful boot on armada-xp.
>>
>>
>> -=-=-=-=-=-=-=-=-=# Don't remove this line #=-=-=-=-=-=-=-=-=-
>> This fixes the following crash at boot:
>>
>>  Unhandled fault: external abort on non-linefetch (0x808) at 0xf00ca018
>>  Internal error: : 808 [#1] SMP ARM
>>
>>  CPU: 2 PID: 1 Comm: swapper/0 Not tainted 4.0.0-rc1 #3
>>  Hardware name: Marvell Armada 370/XP (Device Tree)
>>  task: ed41e800 ti: ed43e000 task.ti: ed43e000
>>  PC is at _set_bit+0x28/0x50
>>  LR is at n_tty_set_termios+0x328/0x358
>>  pc : [<c01bc858>]    lr : [<c0207314>]    psr: 40000113
>>  sp : ed43fd00  ip : 00000000  fp : 00000000
>>  r10: 00000002  r9 : 00000000  r8 : ec930200
>>  r7 : 00000000  r6 : f00ca018  r5 : f00ca000  r4 : ed69cc00
>>  r3 : 00002000  r2 : 00002000  r1 : f00ca018  r0 : 00000000
>>  Flags: nZcv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment kernel
>>  Control: 10c5387d  Table: 0000406a  DAC: 00000015
>>  Process swapper/0 (pid: 1, stack limit = 0xed43e220)
>>
>> The offending instruction in _set_bit() is "strex r0, r2, [r1]"
>> For some reason the exclusive access instructions do not like the
>> vmalloc() space... While there may be another fix to make them
>> fine about vmalloc() space, it still looks like a good idea to
>> use kmalloc() for allocating a small (sub-page) struct.
> NAK.
>
> struct n_tty_data is order 2, not sub-page.
OK, you are right, sorry. 8844 bytes.
Is this really a target for vmalloc() though? I thought kmalloc()
is preferable even for that size.

> The abort means something else is wrong; that's what needs
> tracking down and fixing.
Yeah, I even mentioned that in a commit log.