From: Qian Cai <cai@lca.pw>
To: Michal Hocko <mhocko@kernel.org>
Cc: Petr Mladek <pmladek@suse.com>,
akpm@linux-foundation.org, sergey.senozhatsky.work@gmail.com,
rostedt@goodmis.org, peterz@infradead.org, linux-mm@kvack.org,
john.ogness@linutronix.de, david@redhat.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk()
Date: Mon, 07 Oct 2019 11:33:27 -0400 [thread overview]
Message-ID: <1570462407.5576.292.camel@lca.pw> (raw)
In-Reply-To: <20191007151237.GP2381@dhcp22.suse.cz>
On Mon, 2019-10-07 at 17:12 +0200, Michal Hocko wrote:
> On Mon 07-10-19 10:59:10, Qian Cai wrote:
> [...]
> > It is almost impossible to eliminate all the indirect call chains from
> > console_sem/console_owner_lock to zone->lock because it is too normal that
> > something later needs to allocate some memory dynamically, so as long as it
> > directly call printk() with zone->lock held, it will be in trouble.
>
> Do you have any example where the console driver really _has_ to
> allocate. Because I have hard time to believe this is going to work at
> all as the atomic context doesn't allow to do any memory reclaim and
> such an allocation would be too easy to fail so the allocation cannot
> really rely on it.
I don't know how to explain to you clearly, but let me repeat again one last
time. There is no necessary for console driver directly to allocate considering
this example,
CPU0: CPU1: CPU2: CPU3:
console_sem->lock zone->lock
pi->lock
pi->lock rq_lock
rq->lock
zone->lock
console_sem->lock
Here it only need someone held the rq_lock and allocate some memory. There is
also true for port_lock. Since the deadlock could involve a lot of CPUs and a
longer lock chain, it is impossible to predict which one to allocate some memory
while held a lock could end up with the same problematic lock chain.
>
> So again, crippling the MM code just because of lockdep false possitives
> or a broken console driver sounds like a wrong way to approach the
> problem.
>
> > [ 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
>
> This is an early init code again so the lockdep sounds like a false
> possitive to me.
This is just a tip of iceberg to show the lock dependency,
console_owner --> port_lock_key
which could easily happen everywhere with a simple printk().
next prev parent reply other threads:[~2019-10-07 15:33 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
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 [this message]
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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