From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
akpm@linux-foundation.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org,
Cong Wang <xiyou.wangcong@gmail.com>,
Dave Hansen <dave.hansen@intel.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Mel Gorman <mgorman@suse.de>, Michal Hocko <mhocko@kernel.org>,
Petr Mladek <pmladek@suse.com>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Vlastimil Babka <vbabka@suse.cz>,
"yuwang.yuwang" <yuwang.yuwang@alibaba-inc.com>
Subject: Re: [PATCH] mm: don't warn about allocations which stall for too long
Date: Thu, 2 Nov 2017 18:14:32 +0900 [thread overview]
Message-ID: <20171102091432.GE655@jagdpanzerIV> (raw)
In-Reply-To: <20171102085313.GD655@jagdpanzerIV>
On (11/02/17 17:53), Sergey Senozhatsky wrote:
> On (10/31/17 15:32), Steven Rostedt wrote:
> [..]
> > (new globals)
> > static DEFINE_SPIN_LOCK(console_owner_lock);
> > static struct task_struct console_owner;
> > static bool waiter;
> >
> > console_unlock() {
> >
> > [ Assumes this part can not preempt ]
> >
> > spin_lock(console_owner_lock);
> > console_owner = current;
> > spin_unlock(console_owner_lock);
>
> + disables IRQs?
>
> > for each message
> > write message out to console
> >
> > if (READ_ONCE(waiter))
> > break;
> >
> > spin_lock(console_owner_lock);
> > console_owner = NULL;
> > spin_unlock(console_owner_lock);
> >
> > [ preemption possible ]
>
> otherwise
>
> printk()
> if (console_trylock())
> console_unlock()
> preempt_disable()
> spin_lock(console_owner_lock);
> console_owner = current;
> spin_unlock(console_owner_lock);
> .......
> spin_lock(console_owner_lock);
> IRQ
> printk()
> console_trylock() // fails so we go to busy-loop part
> spin_lock(console_owner_lock); << deadlock
>
>
> even if we would replace spin_lock(console_owner_lock) with IRQ
> spin_lock, we still would need to protect against IRQs on the very
> same CPU. right? IOW, we need to store smp_processor_id() of a CPU
> currently doing console_unlock() and check it in vprintk_emit()?
a major self-correction:
> and we need to protect the entire console_unlock() function. not
> just the printing loop, otherwise the IRQ CPU will spin forever
> waiting for itself to up() the console_sem.
this part is wrong. should have been
"we need to protect the entire printing loop"
so now console_unlock()'s printing loop is going to run
a) under preempt_disable()
b) under local_irq_save()
which is risky.
-ss
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next prev parent reply other threads:[~2017-11-02 9:14 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-26 11:28 [PATCH] mm: don't warn about allocations which stall for too long Tetsuo Handa
2017-10-26 11:41 ` Michal Hocko
2017-11-08 10:30 ` peter enderborg
2017-11-09 8:52 ` Michal Hocko
2017-11-09 9:34 ` peter enderborg
2017-11-09 10:09 ` Michal Hocko
2017-11-09 10:19 ` Tetsuo Handa
2017-10-26 14:37 ` Johannes Weiner
2017-10-31 19:32 ` Steven Rostedt
2017-11-01 8:30 ` Vlastimil Babka
2017-11-01 13:38 ` Petr Mladek
2017-11-01 15:36 ` Steven Rostedt
2017-11-02 11:46 ` Petr Mladek
2017-11-02 14:49 ` Steven Rostedt
2017-11-01 15:33 ` Steven Rostedt
2017-11-01 17:42 ` Vlastimil Babka
2017-11-01 17:54 ` Steven Rostedt
2017-11-02 8:53 ` Sergey Senozhatsky
2017-11-02 9:14 ` Sergey Senozhatsky [this message]
2017-11-02 14:55 ` Steven Rostedt
2017-11-02 12:55 ` Michal Hocko
2017-11-02 15:56 ` Steven Rostedt
2017-11-02 17:06 ` [PATCH v2] printk: Add console owner and waiter logic to load balance console writes Steven Rostedt
2017-11-02 17:10 ` Steven Rostedt
2017-11-02 17:38 ` Steven Rostedt
2017-11-03 10:19 ` Jan Kara
2017-11-03 11:18 ` Steven Rostedt
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