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From: Michal Hocko <mhocko@kernel.org>
To: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	linux-mm@kvack.org, linux-next@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: [linux-next: Tree for Jun 1] __khugepaged_exit rwsem_down_write_failed lockup
Date: Fri, 3 Jun 2016 11:55:49 +0200	[thread overview]
Message-ID: <20160603095549.GD20676@dhcp22.suse.cz> (raw)
In-Reply-To: <20160603084347.GA502@swordfish>

On Fri 03-06-16 17:43:47, Sergey Senozhatsky wrote:
> On (06/03/16 09:25), Michal Hocko wrote:
> > > it's quite hard to trigger the bug (somehow), so I can't
> > > follow up with more information as of now.
> 
> either I did something very silly fixing up the patch, or the
> patch may be causing general protection faults on my system.
> 
> 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?

> 	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?
---
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 6574c62ca4a3..e6f4e6fd587a 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2021,6 +2021,8 @@ void __khugepaged_exit(struct mm_struct *mm)
 	spin_lock(&khugepaged_mm_lock);
 	mm_slot = get_mm_slot(mm);
 	if (mm_slot) {
+		if (khugepaged_scan.mm_slot == mm_slot)
+			khugepaged_scan.mm_slot = NULL;
 		collect_mm_slot(mm_slot);
 		clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
 	}
-- 
Michal Hocko
SUSE Labs

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  reply	other threads:[~2016-06-03  9:55 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-01  3:11 linux-next: Tree for Jun 1 Stephen Rothwell
2016-06-02  1:48 ` [linux-next: Tree for Jun 1] __khugepaged_exit rwsem_down_write_failed lockup Sergey Senozhatsky
2016-06-02  9:21   ` Michal Hocko
2016-06-02 12:08     ` Sergey Senozhatsky
2016-06-02 12:21       ` Michal Hocko
2016-06-03 13:51         ` Andrea Arcangeli
2016-06-03 14:46           ` Michal Hocko
2016-06-03 15:10             ` Andrea Arcangeli
2016-06-07  7:34               ` Michal Hocko
2016-06-08  8:19               ` Vlastimil Babka
2016-06-03  7:15     ` Sergey Senozhatsky
2016-06-03  7:25       ` Michal Hocko
2016-06-03  8:43         ` Sergey Senozhatsky
2016-06-03  9:55           ` Michal Hocko [this message]
2016-06-03 10:05             ` Michal Hocko
2016-06-03 13:38               ` Sergey Senozhatsky
2016-06-03 13:45                 ` Michal Hocko
2016-06-03 13:49                   ` Michal Hocko
2016-06-04  7:51                     ` Sergey Senozhatsky
2016-06-06  8:39                       ` Michal Hocko
2016-06-02 13:24   ` Vlastimil Babka
2016-06-02 18:58     ` Ebru Akagunduz
2016-06-03  1:00       ` Sergey Senozhatsky
2016-06-03  1:29         ` Sergey Senozhatsky
2016-06-03  4:14           ` Sergey Senozhatsky
2016-06-03 12:28     ` [PATCH] mm, thp: fix locking inconsistency in collapse_huge_page Ebru Akagunduz
2016-06-06 13:05       ` Vlastimil Babka
2016-06-09  3:51         ` Sergey Senozhatsky

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