Re: BUG: unable to handle kernel paging request from pty_write [was: Linux 4.4.2]
From: Peter Hurley
Date: Thu Feb 25 2016 - 19:38:49 EST
On 02/25/2016 02:33 PM, Peter Hurley wrote:
> On 02/25/2016 01:32 PM, Jiri Slaby wrote:
>> On 02/25/2016, 09:51 PM, Linus Torvalds wrote:
>>> Jiri, can you check your try_to_wake_up() disassembly for some
>>> indirect "jmp" instructions?
>> Nope, there is none.
>> I will reply to all your questions tomorrow.
>> Just quickly, as I have to go (and don't want you to duplicate efforts)
>> the kernel which was used can be obtained here:
>> The issue is very weird, indeed, this is what I noted to our bugzilla:
>> The stack trace ends in call of try_to_wake_up. Then, there it has to be
>> some of the indirect calls:
>> callq *0x40(%rax)
>> p->sched_class->select_task_rq from select_task_rq
>> RAX is 0x00000000bb37e180, barely can be read with offset 0x40
>> callq *0xd85656(%rip) # ffffffff81e2aba0 <smp_ops+0x20>
>> smp_ops.smp_send_reschedule from ttwu_queue_remote
>> Which hardly can be it, given smp_ops is static.
>> So it has to be some other "call *" from a nested function :(.
>> Interestingly, RBP contains address inside try_to_wake_up --
>> ffffffff810a535a (dunno why) which is:
>> ffffffff810a5355: e8 66 a0 ff ff callq ffffffff8109f3c0
>> ffffffff810a535a: e9 9d fe ff ff jmpq ffffffff810a51fc
> That would imply that RSP was off by +8 when the ttwu_stat() epilog was
> executed so that RBP <= ret addr and RIP <= some local var in try_to_wake_up()
> stack frame.
> Looks like R15 in the crash report could be what RBP should have been.
> Now to find out why RSP is +8
Which I would investigate if I could download that kernel.
Unfortunately, OBS doesn't like me so if you could make that
kernel available some other way or send me a mixed listing
>> ttwu_stat does in the begginning:
>> mov $0x16e80,%r14
>> which is what we actually still have in r14 when it crashes. The first
>> ttwu_stat's "if" has to go through the true branch (otherwise r14 would
>> be overwritten).
>> Another note: we die when jmp/calling to 0xffff88023fd40000.
>> RSI=RDI=0xffff88023fdd6e80. RSI-RIP is 0x96e80, which is R14 + 0x80000.