linux-kernel - Re: [linux-next: Tree for Jun 1] __khugepaged_exit rwsem_down_write

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Date:	Fri, 3 Jun 2016 22:38:13 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:	Michal Hocko <mhocko@...nel.org>
Cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>, linux-mm@...ck.org,
	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [linux-next: Tree for Jun 1] __khugepaged_exit
 rwsem_down_write_failed lockup

On (06/03/16 12:05), Michal Hocko wrote:
> > > RIP collect_mm_slot() + 0x42/0x84
> > > 	khugepaged
> > 
> > So is this really collect_mm_slot called directly from khugepaged or is
> > some inlining going on there?

inlining I suppose.

> > > 	prepare_to_wait_event
> > > 	maybe_pmd_mkwrite
> > > 	kthread
> > > 	_raw_sin_unlock_irq
> > > 	ret_from_fork
> > > 	kthread_create_on_node
> > > 
> > > collect_mm_slot() + 0x42/0x84 is
> > 
> > I guess that the problem is that I have missed that __khugepaged_exit
> > doesn't clear the cached khugepaged_scan.mm_slot. Does the following on
> > top fixes that?
> 
> That wouldn't be sufficient after a closer look. We need to do the same
> from khugepaged_scan_mm_slot when atomic_inc_not_zero fails. So I guess
> it would be better to stick it into collect_mm_slot.

Michal, I'll try to test during the weekend (away from the affected box
now), but in the worst case it can as late as next Thursday (gonna travel
next week).

	-ss