From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Sasha Levin <sashal@kernel.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Daniel Wang <wonderfly@google.com>,
Petr Mladek <pmladek@suse.com>,
Steven Rostedt <rostedt@goodmis.org>,
stable@vger.kernel.org, Alexander.Levin@microsoft.com,
Andrew Morton <akpm@linux-foundation.org>,
byungchul.park@lge.com, dave.hansen@intel.com,
hannes@cmpxchg.org, jack@suse.cz, linux-kernel@vger.kernel.org,
linux-mm@kvack.org,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Mel Gorman <mgorman@suse.de>,
mhocko@kernel.org, pavel@ucw.cz,
penguin-kernel@i-love.sakura.ne.jp,
Peter Zijlstra <peterz@infradead.org>,
tj@kernel.org, Linus Torvalds <torvalds@linux-foundation.org>,
vbabka@suse.cz, Cong Wang <xiyou.wangcong@gmail.com>,
Peter Feiner <pfeiner@google.com>
Subject: Re: 4.14 backport request for dbdda842fe96f: "printk: Add console owner and waiter logic to load balance console writes"
Date: Wed, 12 Dec 2018 17:10:34 +0900 [thread overview]
Message-ID: <20181212081034.GA32687@jagdpanzerIV> (raw)
In-Reply-To: <20181212064841.GB2746@sasha-vm>
On (12/12/18 01:48), Sasha Levin wrote:
> > > > I guess we still don't have a really clear understanding of what exactly
> > > is going in your system
> > >
> > > I would also like to get to the bottom of it. Unfortunately I haven't
> > > got the expertise in this area nor the time to do it yet. Hence the
> > > intent to take a step back and backport Steven's patch to fix the
> > > issue that has resurfaced in our production recently.
> >
> > No problem.
> > I just meant that -stable people can be a bit "unconvinced".
>
> The -stable people tried adding this patch back in April, but ended up
> getting complaints up the wazoo (https://lkml.org/lkml/2018/4/9/154)
> about how this is not -stable material.
OK, really didn't know that! I wasn't Cc-ed on that AUTOSEL email,
and I wasn't Cc-ed on this whole discussion and found it purely
accidentally while browsing linux-mm list.
I understand what Petr meant by his email. Not arguing; below are just
my 5 cents.
> So yes, testing/acks welcome :)
OK. The way I see it (and I can be utterly wrong here):
The patch set in question, most likely and probably (*and those are
theories*), makes panic() deadlock less likely because panic_cpu waits
for console_sem owner to release uart_port/console_owner locks before
panic_cpu pr_emerg("Kernel panic - not syncing"), dump_stack()-s and
brings other CPUs down via stop IPI or NMI.
So a precondition is
panic CPU != uart_port->lock owner CPU
If the panic happens on the same CPU which holds the uart_port spin_lock,
then the deadlock is still there, just like before; we have another patch
which attempts to fix this (it makes console drivers re-entrant from
panic()).
So if you are willing to backport this set to -stable, then I wouldn't
mind, probably would be more correct if we don't advertise this as a
"panic() deadlock fix" tho; we know that deadlock is still possible.
And there will be another -stable backport request in a week or so.
In the meantime, I can add my Acked-by to this backport if it helps.
/* Assuming that my theories explain what's happening with
Daniel's systems. */
-ss
next prev parent reply other threads:[~2018-12-12 8:10 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-27 19:46 4.14 backport request for dbdda842fe96f: "printk: Add console owner and waiter logic to load balance console writes" Daniel Wang
2018-10-01 19:23 ` Steven Rostedt
2018-10-01 20:13 ` Pavel Machek
2018-10-01 20:21 ` Vlastimil Babka
2018-10-01 20:38 ` Daniel Wang
2018-10-01 20:29 ` Steven Rostedt
2018-10-01 20:37 ` Daniel Wang
2018-10-01 20:40 ` Sasha Levin
2018-10-02 8:42 ` Petr Mladek
2018-10-02 17:21 ` Daniel Wang
2018-10-03 0:15 ` Daniel Wang
2018-10-03 1:23 ` Steven Rostedt
2018-10-03 9:14 ` Petr Mladek
2018-10-03 17:16 ` Daniel Wang
2018-10-03 17:37 ` Steven Rostedt
2018-10-03 18:37 ` Daniel Wang
2018-10-03 23:37 ` Daniel Wang
2018-10-04 7:44 ` Sergey Senozhatsky
2018-10-04 8:05 ` Sergey Senozhatsky
2018-10-04 8:36 ` Petr Mladek
2018-10-04 8:55 ` Sergey Senozhatsky
2018-10-21 18:09 ` Daniel Wang
2018-10-22 9:32 ` Petr Mladek
2018-10-22 10:09 ` Sergey Senozhatsky
2018-11-01 16:05 ` Daniel Wang
2018-11-09 6:47 ` Sergey Senozhatsky
2018-12-12 1:16 ` Daniel Wang
2018-12-12 5:21 ` Sergey Senozhatsky
2018-12-12 6:08 ` Daniel Wang
2018-12-12 6:28 ` Sergey Senozhatsky
2018-12-12 6:48 ` Sasha Levin
2018-12-12 8:10 ` Sergey Senozhatsky [this message]
2018-12-12 13:36 ` Petr Mladek
2018-12-12 13:59 ` Sergey Senozhatsky
2018-12-12 17:43 ` Sasha Levin
2018-12-12 20:11 ` Daniel Wang
2018-12-12 21:43 ` Sasha Levin
2018-12-12 21:49 ` Daniel Wang
2018-12-12 21:52 ` Sasha Levin
2018-12-12 21:56 ` Daniel Wang
2018-12-13 0:40 ` Daniel Wang
2018-12-13 2:27 ` Sergey Senozhatsky
2018-12-13 2:39 ` Daniel Wang
2018-12-13 9:59 ` Petr Mladek
2018-12-13 14:29 ` Sasha Levin
2018-12-13 2:07 ` Sergey Senozhatsky
2018-12-28 0:16 ` Sergey Senozhatsky
2018-12-28 8:27 ` Greg KH
2018-12-28 22:03 ` Daniel Wang
2018-12-30 3:03 ` Sergey Senozhatsky
2018-10-04 7:49 ` Petr Mladek
2018-10-02 8:16 ` Sergey Senozhatsky
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