Re: [PATCH 02/20] SUNRPC: add 'struct cred *' to auth_cred and rpc_cred

[NeilBrown <neilb@suse.com>]

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On Thu, Jan 18 2018, Anna Schumaker wrote:

> On 01/18/2018 01:39 PM, Anna Schumaker wrote:
>> Hi Neil,
>> 
>> On 01/08/2018 12:26 AM, NeilBrown wrote:
>>> The SUNRPC credential framework was put together before
>>> Linux has 'struct cred'.  Now that we have it, it makes sense to
>>> use it.
>>> This first step just includes a suitable 'struct cred *' pointer
>>> in every 'struct auth_cred' and almost every 'struct rpc_cred'.
>>>
>>> The rpc_cred used for auth_null has a NULL 'struct cred *' as nothing
>>> else really makes sense.
>>>
>>> For rpc_cred, the pointer is reference counted.
>>> For auth_cred it isn't.  struct auth_cred are either allocated on
>>> the stack, in which case the thread owns a reference to the auth,
>>> or are part of 'struct generic_cred' in which case gc_base owns the
>>> reference and acred shares it.
>
> This patch is also causing a kernel panic for me if I mount using sec=krb5, run cthon tests, and then unmount.  Here is the log message I'm getting:
>
> [   82.599174] Kernel panic - not syncing: CRED: put_cred_rcu() sees 00000000f5847a57 with usage -1
> [   82.599174]
> [   82.600227] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.15.0-rc7-ANNA+ #14336
> [   82.600801] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
> [   82.601435] Call Trace:
> [   82.601639]  <IRQ>
> [   82.601830]  dump_stack+0x5c/0x7e
> [   82.602125]  panic+0xdf/0x228
> [   82.602383]  ? try_to_wake_up+0x24b/0x420
> [   82.602853]  put_cred_rcu+0x8a/0x90
> [   82.603183]  rcu_process_callbacks+0x1ab/0x4f0
> [   82.603577]  __do_softirq+0xcc/0x305
> [   82.603881]  irq_exit+0xa9/0xb0
> [   82.604159]  smp_apic_timer_interrupt+0x5b/0x140
> [   82.604528]  apic_timer_interrupt+0x98/0xa0
> [   82.604892]  </IRQ>
> [   82.605133] RIP: 0010:native_safe_halt+0x2/0x10
> [   82.605678] RSP: 0018:ffffffff82003ea8 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff11
> [   82.606619] RAX: 0000000080000000 RBX: 0000000000000000 RCX: 0000000000000000
> [   82.607270] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
> [   82.608077] RBP: 0000000000000000 R08: 0000000000000002 R09: 000000000001ea40
> [   82.609066] R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000000
> [   82.609951] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
> [   82.610771]  default_idle+0x15/0x120
> [   82.611128]  do_idle+0x15c/0x1c0
> [   82.611371]  cpu_startup_entry+0x6a/0x70
> [   82.611762]  start_kernel+0x445/0x465
> [   82.612104]  secondary_startup_64+0xa5/0xb0
> [   82.612561] Kernel Offset: disabled
> [   82.612862] ---[ end Kernel panic - not syncing: CRED: put_cred_rcu() sees 00000000f5847a57 with usage -1
> [   82.612862]
>

That's not good.

I've just read through the patches again and didn't find anything that
could cause this, so I must have missed something.

You say "This patch is also causing", but I assume it is the whole patch
set rather than just this one patch -  is that correct?

Also, have you run tests without sec=krb5 and not had the error?

I'll try to set up some more thorough testing myself.

Thanks,
NeilBrown

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