Re: [PATCH v1 00/12] netoops support

Américo Wang
2010-11-04T06:30:31Z

On Wed, Nov 03, 2010 at 06:18:41PM -0700, Mike Waychison wrote:
>Matt Mackall wrote:
>>On Wed, 2010-11-03 at 13:29 -0700, Mike Waychison wrote:
>>>Mike Waychison wrote:
>>>>FWIW, another semantic difference between netconsole and netoops (that
>>>>I had missed in the last email) is filtering: we really do want to get
>>>>the whole log when a crash happens, debug messages and all.
>>>>Netconsole is subject to console filtering (which we _do_ want as
>>>>debug messages going out the uart slows the whole world down).
>>>>
>>>>netconsole and netoops _do_ have bits in common, for instance the
>>>>handling of NETDEV events and source+target configuration. I'd rather
>>>>those bits become common between the two than figure out how to jam
>>>>the semantics we need into netconsole.
>>>Hi Matt,
>>>
>>>I've been reading through the netconsole driver in response to
>>>Greg's comments on this thread, and it is definitely more robust
>>>in terms of configuration and handling of network device events
>>>than the netoops driver I proposed.
>>
>>I've been following the discussion to see if it went anywhere
>>interesting..
>>
>>>What are your thoughts on extending netconsole with the same sort
>>>of semantics that are in the netoops patchset?
>>
>>My first thought is that it's a bit unfortunate that some of the the
>>netconsole configgy bits weren't implemented in a generic way that would
>>be applicable to other netpoll clients. Some people have never gotten it
>>into their heads that netconsole isn't the only client.
>>
>>>I'd still like to have blit-dmesg-to-the-network-on-oops
>>>semantics, which seems doable by having a per-target flag for
>>>streaming of console messages (enabled by default) and a flag to
>>>emit a structured full dmesg dump (disabled by default).
>>
>>I'd actually like to see you go forward with netoops. It's clear to me
>>that it's a different beast and complexifying netconsole with a bunch of
>>weird new options doesn't really sit well. If that means abstracting
>>some of the sysfs crap from netconsole, great.
>
>I'd be happy to take a stab at this. This solves most of the ABI
>reservations that I have with this v1 patchset.
>
>Looking at netconsole, it looks to lack some locking for data
>consistency, and it appears that we will deadlock if we ever get a
>NETDEV_UNREGISTER event (due to recursively grabbing the rtnl in
>netpoll_cleanup). I have a couple patches I've been hacking on this
>afternoon that should clear those issues up.
>

You might want to look at net-next-2.6, it has some fixes
from Neil.

>I'm thinking of pushing all the target handling options down into
>net/core/netpoll.c. I'll probably expose this interface as "struct
>netpoll_targets" where ->lock and ->list could be completely exposed
>to clients. netconsole would then get a lot smaller as would
>netoops.
>
>>That said, I don't think netoops is an ideal name, given how closely
>>bound oops _events_ are with their textual output. Presumably it covers
>>events other than oopsen like panics too.
>
>True. We call this code 'netdump' or 'network_dumper' internally,
>but I figured it'd be better to follow current conventions with
>ramoops and mtdoops already in the tree. I don't really care what
>it's called in the end :)
>

"netdump" was used by a utility that do crash dumping over net.
It is deprecated now, since we have kdump.

>>
>>Regarding rolling oopses: lots of machines regularly survive
>>oopses, so I think you ought to consider rate-limiting them (to a
>>configurable rate
>>with a very low default) rather than suppressing all but the first.
>>
>
>The trouble with Oopses is just that: We don't know whether we can
>safely survive them or not and it's a total gamble each time we do
>Oops. We can't programmatically know how crapped out the machine is,
>so historically we've erred on not allowing bad things to continue
>happening once someone notices something wrong.
>
>It's easier for us to just shoot the machine in the head
>(panic_on_oops) and move on than corrupt data or dead-lock in weird
>ways at some later point in time. This is definitely not the
>behaviour I would want nor expect from my desktop or phone, but for
>the cluster, it's just safer.

We also have pause_on_oops, or we can invent a oops_once.