Re: [dpdk-dev] [PATCH v2 1/6] eal: introduce oops handling API

From: Jerin Jacob <jerinjacobk@gmail.com>
To: Stephen Hemminger <stephen@networkplumber.org>
Cc: Jerin Jacob <jerinj@marvell.com>, dpdk-dev <dev@dpdk.org>,
	 Bruce Richardson <bruce.richardson@intel.com>,
	Ray Kinsella <mdr@ashroe.eu>,
	 Thomas Monjalon <thomas@monjalon.net>,
	David Marchand <david.marchand@redhat.com>,
	 Dmitry Kozlyuk <dmitry.kozliuk@gmail.com>,
	 Narcisa Ana Maria Vasile <navasile@linux.microsoft.com>,
	 "Dmitry Malloy (MESHCHANINOV)" <dmitrym@microsoft.com>,
	Pallavi Kadam <pallavi.kadam@intel.com>,
	 "Ananyev, Konstantin" <konstantin.ananyev@intel.com>,
	 "Ruifeng Wang (Arm Technology China)" <ruifeng.wang@arm.com>,
	Jan Viktorin <viktorin@rehivetech.com>,
	 David Christensen <drc@linux.vnet.ibm.com>
Subject: Re: [dpdk-dev] [PATCH v2 1/6] eal: introduce oops handling API
Date: Tue, 17 Aug 2021 13:08:46 +0530	[thread overview]
Message-ID: <CALBAE1PHfmVDKLjT5pQAx_DZZtKCxbLrdCJKBWaOCCR0NbnJYw@mail.gmail.com> (raw)
In-Reply-To: <20210816205345.6d686c7d@hermes.local>

On Tue, Aug 17, 2021 at 9:23 AM Stephen Hemminger
<stephen@networkplumber.org> wrote:
>
> On Tue, 17 Aug 2021 08:57:18 +0530
> <jerinj@marvell.com> wrote:
>
> > From: Jerin Jacob <jerinj@marvell.com>
> >
> > Introducing oops handling API with following specification
> > and enable stub implementation for Linux and FreeBSD.
> >
> > On rte_eal_init() invocation, the EAL library installs the
> > oops handler for the essential signals.
> > The rte_oops_signals_enabled() API provides the list
> > of signals the library installed by the EAL.
>
> This is a big change, and many applications already handle these
> signals themselves. Therefore adding this needs to be opt-in
> and not enabled by default.

In order to avoid every application explicitly register this
sighandler and to cater to the
co-existing application-specific signal-hander usage.
The following design has been chosen. (It is mentioned in the commit log,
I will describe here for more clarity)

Case 1:
a) The application installs the signal handler prior to rte_eal_init().
b) Implementation stores the application-specific signal and replace a
signal handler as oops eal handler
c) when application/DPDK get the segfault, the default EAL oops
handler gets invoked
d) Then it dumps the EAL specific message, it calls the
application-specific signal handler
installed in step 1 by application. This avoids breaking any contract
with the application.
i.e Behavior is the same current EAL now.
That is the reason for not using SA_RESETHAND(which call SIG_DFL after
eal oops handler instead
application-specific handler)

Case 2:
a) The application install the signal handler after rte_eal_init(),
b) EAL hander get replaced with application handle then the application can call
rte_oops_decode() to decode.

In order to cater the above use case, rte_oops_signals_enabled() and
rte_oops_decode()
provided.

Here we are not breaking any contract with the application.
Do you have concerns about this design?