linux-kernel - Re: [PATCH V2 06/10] Drivers: hv: vmbus: use 'die' notification chain instead of 'panic'

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Message-ID: <87wpys3tov.fsf@vitty.brq.redhat.com>
Date:	Thu, 25 Jun 2015 13:37:20 +0200
From:	Vitaly Kuznetsov <vkuznets@...hat.com>
To:	"K. Y. Srinivasan" <kys@...rosoft.com>
Cc:	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	devel@...uxdriverproject.org, olaf@...fle.de, apw@...onical.com,
	jasowang@...hat.com
Subject: Re: [PATCH V2 06/10] Drivers: hv: vmbus: use 'die' notification chain instead of 'panic'

"K. Y. Srinivasan" <kys@...rosoft.com> writes:

> From: Vitaly Kuznetsov <vkuznets@...hat.com>
>
> current_pt_regs() returns regs of the userspace process and in case of
> kernel crash this is not what we need to report. E.g. when we trigger
> crash with sysrq we see the following:
> ...
>  RIP: 0010:[<ffffffff815b8696>]  [<ffffffff815b8696>] sysrq_handle_crash+0x16/0x20
>  RSP: 0018:ffff8800db0a7d88  EFLAGS: 00010246
>  RAX: 000000000000000f RBX: ffffffff820a0660 RCX: 0000000000000000
> ...
> at the same time current_pt_regs() give us:
> ip=7f899ea7e9e0, ax=ffffffffffffffda, bx=26c81a0, cx=7f899ea7e9e0, ...
> These registers come from the userspace process triggered the crash. As we
> don't even know which process it was this information is rather useless.
>
> When kernel crash happens proper regs are being passed to all receivers on
> the die_chain (and panic_notifier_list is being notified with the string
> passed to panic() only). Let's move our Hyper-V MSR reporter there. This
> change has the following implication: when panic() is called manually from
> some other part of kernel we won't be reporting crash to the hypervisor
> (but we have no valuable information to report anyway).

We can, actually, do better: we can has this reporter in _both_
notification chains (with a static preventng double reporting). In this
case we'll have panics reported on e.g BUG_ON()

As this patch is still not merged I'll fix and resend instead of
creating a separate patch.

-- 
  Vitaly
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