linux-mm.kvack.org archive mirror
 help / color / mirror / Atom feed
From: Petr Mladek <pmladek@suse.com>
To: Qian Cai <cai@lca.pw>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	sergey.senozhatsky.work@gmail.com, rostedt@goodmis.org,
	peterz@infradead.org, Michal Hocko <mhocko@kernel.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: Thu, 10 Oct 2019 09:57:56 +0200	[thread overview]
Message-ID: <20191010075756.nyix7l32ai6fylzn@pathway.suse.cz> (raw)
In-Reply-To: <1570632374.5937.8.camel@lca.pw>

On Wed 2019-10-09 10:46:14, Qian Cai wrote:
> 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.

No, we just do not want to comlicate the code too much just to hide
false positives from lockdep.

I do not ask you to reproduce the deadlock. I ask you to find
a code path where the deadlock might really happen. It seems
that you actually found one in the tty code in the other mail.

Best Regards,
Petr


  reply	other threads:[~2019-10-10  7:58 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
2019-10-10  7:57                                 ` Petr Mladek [this message]
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20191010075756.nyix7l32ai6fylzn@pathway.suse.cz \
    --to=pmladek@suse.com \
    --cc=akpm@linux-foundation.org \
    --cc=borntraeger@de.ibm.com \
    --cc=cai@lca.pw \
    --cc=david@redhat.com \
    --cc=gor@linux.ibm.com \
    --cc=heiko.carstens@de.ibm.com \
    --cc=john.ogness@linutronix.de \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=mhocko@kernel.org \
    --cc=oberpar@linux.ibm.com \
    --cc=peterz@infradead.org \
    --cc=rostedt@goodmis.org \
    --cc=sergey.senozhatsky.work@gmail.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).