linux-kernel - Re: 4.14 backport request for dbdda842fe96f: "printk: Add console owner and waiter logic to load balance console writes"

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Message-ID: <20181004080506.GB12879@jagdpanzerIV>
Date:   Thu, 4 Oct 2018 17:05:06 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Daniel Wang <wonderfly@...gle.com>
Cc:     rostedt@...dmis.org, Petr Mladek <pmladek@...e.com>,
        stable@...r.kernel.org, Alexander.Levin@...rosoft.com,
        akpm@...ux-foundation.org, byungchul.park@....com,
        dave.hansen@...el.com, hannes@...xchg.org, jack@...e.cz,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Mel Gorman <mgorman@...e.de>, mhocko@...nel.org, pavel@....cz,
        penguin-kernel@...ove.sakura.ne.jp, peterz@...radead.org,
        tj@...nel.org, torvalds@...ux-foundation.org, vbabka@...e.cz,
        Cong Wang <xiyou.wangcong@...il.com>,
        Peter Feiner <pfeiner@...gle.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: 4.14 backport request for dbdda842fe96f: "printk: Add console
 owner and waiter logic to load balance console writes"

On (10/04/18 16:44), Sergey Senozhatsky wrote:
> So... Just an idea. Can you try a very dirty hack? Forcibly increase
> oops_in_progress in panic() before console_flush_on_panic(), so 8250
> serial8250_console_write() will use spin_trylock_irqsave() and maybe
> avoid deadlock.

E.g. something like below?
[this is not a patch; just a theory]:

---

diff --git a/kernel/panic.c b/kernel/panic.c
index 8b2e002d52eb..188338a55d1c 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -233,7 +233,13 @@ void panic(const char *fmt, ...)
 	if (_crash_kexec_post_notifiers)
 		__crash_kexec(NULL);
 
+	/*
+	 * Decrement oops_in_progress and let bust_spinlocks() to
+	 * unblank_screen(), console_unblank() and wake_up_klogd()
+	 */
 	bust_spinlocks(0);
+	/* Set oops_in_progress, so we can reenter serial console driver*/
+	bust_spinlocks(1);
 
 	/*
 	 * We may have ended up stopping the CPU holding the lock (in