Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Message-ID: <1570628593.5937.3.camel@lca.pw>
Subject: Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk()
From:   Qian Cai <cai@lca.pw>
To:     Michal Hocko <mhocko@kernel.org>
Cc:     Petr Mladek <pmladek@suse.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        sergey.senozhatsky.work@gmail.com, rostedt@goodmis.org,
        peterz@infradead.org, linux-mm@kvack.org,
        john.ogness@linutronix.de, akpm@linux-foundation.org,
        Vasily Gorbik <gor@linux.ibm.com>,
        Peter Oberparleiter <oberpar@linux.ibm.com>, david@redhat.com,
        linux-kernel@vger.kernel.org
Date:   Wed, 09 Oct 2019 09:43:13 -0400
In-Reply-To: <20191009132746.GA6681@dhcp22.suse.cz>
References: <20191008074357.f33f6pbs4cw5majk@pathway.suse.cz>
         <20191008082752.GB6681@dhcp22.suse.cz>
         <aefe7f75-b0ec-9e99-a77e-87324edb24e0@de.ibm.com>
         <1570550917.5576.303.camel@lca.pw> <20191008183525.GQ6681@dhcp22.suse.cz>
         <1570561573.5576.307.camel@lca.pw> <20191008191728.GS6681@dhcp22.suse.cz>
         <1570563324.5576.309.camel@lca.pw>
         <20191009114903.aa6j6sa56z2cssom@pathway.suse.cz>
         <1570626402.5937.1.camel@lca.pw> <20191009132746.GA6681@dhcp22.suse.cz>
Content-Type: text/plain; charset="UTF-8"
Mime-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Wed, 2019-10-09 at 15:27 +0200, Michal Hocko wrote:
> On Wed 09-10-19 09:06:42, Qian Cai wrote:
> [...]
> > https://lore.kernel.org/linux-mm/1570460350.5576.290.camel@lca.pw/
> > 
> > [  297.425964] -> #1 (&port_lock_key){-.-.}:
> > [  297.425967]        __lock_acquire+0x5b3/0xb40
> > [  297.425967]        lock_acquire+0x126/0x280
> > [  297.425968]        _raw_spin_lock_irqsave+0x3a/0x50
> > [  297.425969]        serial8250_console_write+0x3e4/0x450
> > [  297.425970]        univ8250_console_write+0x4b/0x60
> > [  297.425970]        console_unlock+0x501/0x750
> > [  297.425971]        vprintk_emit+0x10d/0x340
> > [  297.425972]        vprintk_default+0x1f/0x30
> > [  297.425972]        vprintk_func+0x44/0xd4
> > [  297.425973]        printk+0x9f/0xc5
> > [  297.425974]        register_console+0x39c/0x520
> > [  297.425975]        univ8250_console_init+0x23/0x2d
> > [  297.425975]        console_init+0x338/0x4cd
> > [  297.425976]        start_kernel+0x534/0x724
> > [  297.425977]        x86_64_start_reservations+0x24/0x26
> > [  297.425977]        x86_64_start_kernel+0xf4/0xfb
> > [  297.425978]        secondary_startup_64+0xb6/0xc0
> > 
> > where the report again show the early boot call trace for the locking
> > dependency,
> > 
> > console_owner --> port_lock_key
> > 
> > but that dependency clearly not only happen in the early boot.
> 
> Can you provide an example of the runtime dependency without any early
> boot artifacts? Because this discussion really doens't make much sense
> without a clear example of a _real_ lockdep report that is not a false
> possitive. All of them so far have been concluded to be false possitive
> AFAIU.

An obvious one is in the above link. Just replace the trace in #1 above with
printk() from anywhere, i.e., just ignore the early boot calls there as they are
 not important.

printk()
  console_unlock()
    console_lock_spinning_enable() --> console_owner_lock
  call_console_drivers()
    serial8250_console_write() --> port->lock