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Date: Mon, 30 Oct 2017 16:22:00 +0100
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: possible deadlock in lru_add_drain_all
Message-ID: <20171030152200.ayfnewoqkxbuk4zh@hirez.programming.kicks-ass.net>
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To: Byungchul Park <byungchul.park@lge.com>
Cc: Michal Hocko <mhocko@kernel.org>, Dmitry Vyukov <dvyukov@google.com>, syzbot <bot+e7353c7141ff7cbb718e4c888a14fa92de41ebaa@syzkaller.appspotmail.com>, Andrew Morton <akpm@linux-foundation.org>, Dan Williams <dan.j.williams@intel.com>, Johannes Weiner <hannes@cmpxchg.org>, Jan Kara <jack@suse.cz>, jglisse@redhat.com, LKML <linux-kernel@vger.kernel.org>, linux-mm@kvack.org, shli@fb.com, syzkaller-bugs@googlegroups.com, Thomas Gleixner <tglx@linutronix.de>, Vlastimil Babka <vbabka@suse.cz>, ying.huang@intel.com, kernel-team@lge.com

On Mon, Oct 30, 2017 at 04:10:09PM +0100, Peter Zijlstra wrote:
> I can indeed confirm it's running old code; cpuhp_state is no more.
> 
> However, that splat translates like:
> 
> 	__cpuhp_setup_state()
> #0	  cpus_read_lock()
> 	  __cpuhp_setup_state_cpuslocked()
> #1	    mutex_lock(&cpuhp_state_mutex)
> 
> 
> 
> 	__cpuhp_state_add_instance()
> #2	  mutex_lock(&cpuhp_state_mutex)
> 	  cpuhp_issue_call()
> 	    cpuhp_invoke_ap_callback()
> #3	      wait_for_completion()
> 
> 						msr_device_create()
> 						  ...
> #4						    filename_create()
> #3						complete()
> 


So all this you can get in a single callchain when you do something
shiny like:

	modprobe msr


> 	do_splice()
> #4	  file_start_write()
> 	  do_splice_from()
> 	    iter_file_splice_write()
> #5	      pipe_lock()
> 	      vfs_iter_write()
> 	        ...
> #6		  inode_lock()
> 
> 

This is a splice into a devtmpfs file


> 	sys_fcntl()
> 	  do_fcntl()
> 	    shmem_fcntl()
> #5	      inode_lock()

#6 (obviously)

> 	      shmem_wait_for_pins()
> 	        if (!scan)
> 		  lru_add_drain_all()
> #0		    cpus_read_lock()
> 

Is the right fcntl()


So 3 different callchains, and *splat*..


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