From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Petr Mladek <pmladek@suse.com>
Cc: Theodore Ts'o <tytso@mit.edu>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Arnd Bergmann <arnd@arndb.de>,
linux-mm@kvack.org, Peter Zijlstra <peterz@infradead.org>,
Catalin Marinas <catalin.marinas@arm.com>,
linux-kernel@vger.kernel.org,
Steven Rostedt <rostedt@goodmis.org>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Qian Cai <cai@lca.pw>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Waiman Long <longman@redhat.com>,
Dan Williams <dan.j.williams@intel.com>,
Will Deacon <will@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
linux-arm-kernel@lists.infradead.org
Subject: Re: printk() + memory offline deadlock (WAS Re: page_alloc.shuffle=1 + CONFIG_PROVE_LOCKING=y = arm64 hang)
Date: Tue, 24 Sep 2019 10:28:34 +0900 [thread overview]
Message-ID: <20190924012834.GC3864@jagdpanzerIV> (raw)
In-Reply-To: <20190923125851.cykw55jpqwlerjrz@pathway.suse.cz>
On (09/23/19 14:58), Petr Mladek wrote:
>
> If I understand it correctly then this is the re-appearing problem.
> The only systematic solution with the current approach is to
> take port->lock in printk_safe/printk_deferred context.
It probably is.
We have a number of reverse paths. TTY invokes MM under port->lock,
UART invokes TTY under port->lock, MM invokes UART under zone->lock,
UART invokes sched under port->lock, shced invokes UART, UART invokes
UART under port->lock (!), and so on.
> But this is a massive change that almost nobody wants. Instead,
> we want the changes that were discussed on Plumbers.
>
> Now, the question is what to do with existing kernels. There were
> several lockdep reports. And I am a bit lost. Did anyone seen
> real deadlocks or just the lockdep reports?
I think so. Qian Cai mentioned "a hang" in one of his reports
(was it unseeded random()?). I'll send a formal patch maybe,
since there were no objections.
> To be clear. I would feel more comfortable when there are no
> deadlocks. But I also do not want to invest too much time
> into old kernels. All these problems were there for ages.
> We could finally see them because lockdep was enabled in printk()
> thanks to printk_safe.
True.
Everyone was so much happier when printk() used to do
lockdep_off();
call_console_drivers();
lockdep_on();
Now we can have lockdep and RCU checks enabled, yet somehow
printk_safe is still "a terrible thing" :)
-ss
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next prev parent reply other threads:[~2019-09-24 1:28 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-22 21:33 page_alloc.shuffle=1 + CONFIG_PROVE_LOCKING=y = arm64 hang Qian Cai
2019-08-23 11:37 ` Will Deacon
2019-08-23 11:52 ` Qian Cai
2019-09-05 21:08 ` Qian Cai
2019-09-10 15:22 ` Qian Cai
2019-09-10 19:49 ` Qian Cai
2019-09-12 2:28 ` CONFIG_SHUFFLE_PAGE_ALLOCATOR=y lockdep splat (WAS Re: page_alloc.shuffle=1 + CONFIG_PROVE_LOCKING=y = arm64 hang) Qian Cai
2019-09-10 20:35 ` page_alloc.shuffle=1 + CONFIG_PROVE_LOCKING=y = arm64 hang Qian Cai
2019-09-11 1:10 ` Sergey Senozhatsky
2019-09-12 12:05 ` Qian Cai
2019-09-16 14:42 ` Steven Rostedt
2019-09-17 0:53 ` Sergey Senozhatsky
2019-09-18 14:39 ` printk() + memory offline deadlock (WAS Re: page_alloc.shuffle=1 + CONFIG_PROVE_LOCKING=y = arm64 hang) Qian Cai
2019-09-18 15:50 ` Sergey Senozhatsky
2019-09-18 15:58 ` Sergey Senozhatsky
2019-09-18 16:10 ` Qian Cai
2019-09-23 10:21 ` Sergey Senozhatsky
2019-09-23 12:58 ` Petr Mladek
2019-09-23 13:24 ` Qian Cai
2019-09-24 1:28 ` Sergey Senozhatsky [this message]
2019-09-23 13:09 ` Qian Cai
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