From: Qian Cai <cai@lca.pw>
To: Petr Mladek <pmladek@suse.com>
Cc: Michal Hocko <mhocko@kernel.org>,
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>,
PeterOberparleiter <oberpar@linux.ibm.com>,
david@redhat.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk()
Date: Wed, 09 Oct 2019 10:46:14 -0400 [thread overview]
Message-ID: <1570632374.5937.8.camel@lca.pw> (raw)
In-Reply-To: <20191009142438.yx74ukfqwy2hr4fz@pathway.suse.cz>
On Wed, 2019-10-09 at 16:24 +0200, Petr Mladek wrote:
> On Wed 2019-10-09 09:43:13, Qian Cai wrote:
> > 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
>
> Please, find the location where this really happens and then suggests
> how the real deadlock could get fixed. So far, we have seen only
> false positives and theoretical scenarios.
Now the bar is higher again. You are now asking me to actually trigger this
potential deadlock live. I am probably better off buying some lottery tickets
then if I could be that lucky.
next prev parent reply other threads:[~2019-10-09 14:46 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-04 22:26 [PATCH v2] mm/page_isolation: fix a deadlock with printk() Qian Cai
2019-10-07 8:07 ` Michal Hocko
2019-10-07 9:05 ` Petr Mladek
2019-10-07 11:33 ` Michal Hocko
2019-10-07 12:34 ` Qian Cai
2019-10-07 11:04 ` Qian Cai
2019-10-07 11:37 ` Michal Hocko
2019-10-07 12:11 ` Qian Cai
2019-10-07 12:43 ` Michal Hocko
2019-10-07 13:07 ` Qian Cai
2019-10-07 14:10 ` Petr Mladek
2019-10-07 14:30 ` Petr Mladek
2019-10-07 14:49 ` Michal Hocko
2019-10-08 7:43 ` Petr Mladek
2019-10-08 8:27 ` Michal Hocko
2019-10-08 12:56 ` Christian Borntraeger
2019-10-08 16:08 ` Qian Cai
2019-10-08 18:35 ` Michal Hocko
2019-10-08 19:06 ` Qian Cai
2019-10-08 19:17 ` Michal Hocko
2019-10-08 19:35 ` Qian Cai
2019-10-09 11:49 ` Petr Mladek
2019-10-09 13:06 ` Qian Cai
2019-10-09 13:27 ` Michal Hocko
2019-10-09 13:43 ` Qian Cai
2019-10-09 13:51 ` Michal Hocko
2019-10-09 14:19 ` Qian Cai
2019-10-09 14:34 ` Michal Hocko
2019-10-09 15:08 ` Qian Cai
2019-10-09 16:23 ` Michal Hocko
2019-10-09 16:23 ` Michal Hocko
2019-10-10 9:01 ` Qian Cai
2019-10-10 10:59 ` Michal Hocko
2019-10-10 13:11 ` Qian Cai
2019-10-10 14:18 ` Michal Hocko
2019-10-10 14:47 ` Qian Cai
2019-10-10 17:30 ` Michal Hocko
2019-10-10 17:48 ` Qian Cai
2019-10-10 18:06 ` Michal Hocko
2019-10-10 18:59 ` David Hildenbrand
2019-10-09 14:24 ` Petr Mladek
2019-10-09 14:46 ` Qian Cai [this message]
2019-10-10 7:57 ` Petr Mladek
2019-10-09 11:39 ` Petr Mladek
2019-10-09 13:56 ` Peter Oberparleiter
2019-10-09 14:26 ` Michal Hocko
2019-10-10 5:12 ` Sergey Senozhatsky
2019-10-10 7:40 ` Michal Hocko
2019-10-10 8:16 ` Sergey Senozhatsky
2019-10-10 8:37 ` Michal Hocko
2019-10-10 8:21 ` Petr Mladek
2019-10-10 8:39 ` Sergey Senozhatsky
2019-10-10 11:11 ` Petr Mladek
2019-10-09 15:25 ` Qian Cai
2019-10-09 15:25 ` Qian Cai
2019-10-07 14:59 ` Qian Cai
2019-10-07 15:12 ` Michal Hocko
2019-10-07 15:33 ` Qian Cai
2019-10-08 8:15 ` Petr Mladek
2019-10-08 9:32 ` Qian Cai
2019-10-08 13:13 ` Steven Rostedt
2019-10-08 13:23 ` Qian Cai
2019-10-08 13:33 ` Steven Rostedt
2019-10-08 13:42 ` Petr Mladek
2019-10-08 13:48 ` Michal Hocko
2019-10-08 14:03 ` Qian Cai
2019-10-08 14:08 ` Michal Hocko
2019-10-08 8:40 ` Michal Hocko
2019-10-08 10:04 ` Qian Cai
2019-10-08 10:39 ` Michal Hocko
2019-10-08 12:00 ` Qian Cai
2019-10-08 12:39 ` Michal Hocko
2019-10-08 13:06 ` Qian Cai
2019-10-08 13:37 ` Michal Hocko
2019-10-08 13:08 ` Petr Mladek
2019-10-08 13:33 ` Qian Cai
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