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From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Ebru Akagunduz <ebru.akagunduz@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>,
	sergey.senozhatsky.work@gmail.com,
	Andrew Morton <akpm@linux-foundation.org>,
	Michal Hocko <mhocko@kernel.org>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Rik van Riel <riel@redhat.com>,
	linux-mm@kvack.org, linux-next@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [linux-next: Tree for Jun 1] __khugepaged_exit rwsem_down_write_failed lockup
Date: Fri, 3 Jun 2016 10:00:36 +0900	[thread overview]
Message-ID: <20160603010036.GA464@swordfish> (raw)
In-Reply-To: <20160602185856.GA3854@debian>

On (06/02/16 21:58), Ebru Akagunduz wrote:
[..]
> > I think it's this patch:
> > 
> > http://ozlabs.org/~akpm/mmots/broken-out/mm-thp-make-swapin-readahead-under-down_read-of-mmap_sem.patch
> > 
> > Some parts of the code in collapse_huge_page() that were under
> > down_write(mmap_sem) are under down_read() after the patch. But
> > there's "goto out" which continues via "goto out_up_write" which
> > does up_write(mmap_sem) so there's an imbalance. One path seems to
> > go via both up_read() and up_write(). I can imagine this can cause a
> > stuck down_write() among other things?
> Recently, I realized the same imbalance, it is an obvious
> inconsistency. I don't know, this issue can be related with
> mine. I'll send a fix patch.

a good find by Vlastimil.

Ebru, can you also re-visit __collapse_huge_page_swapin()? it's called
from collapse_huge_page() under the down_read(&mm->mmap_sem), is there
any reason to do the nested down_read(&mm->mmap_sem)?

collapse_huge_page()
...
	down_read(&mm->mmap_sem);
	result = hugepage_vma_revalidate(mm, vma, address);
	if (result)
		goto out;

	pmd = mm_find_pmd(mm, address);
	if (!pmd) {
		result = SCAN_PMD_NULL;
		goto out;
	}

	if (allocstall == curr_allocstall && swap != 0) {
		if (!__collapse_huge_page_swapin(mm, vma, address, pmd)) {
			{
			:	if (ret & VM_FAULT_RETRY) {
			:		down_read(&mm->mmap_sem);
			:		^^^^^^^^^
			:		if (hugepage_vma_revalidate(mm, vma, address))
			:			return false;
			:	}
			}

			up_read(&mm->mmap_sem);
			goto out;
		}
	}

	up_read(&mm->mmap_sem);



so if __collapse_huge_page_swapin() retruns true we have:
	- down_read() twice, up_read() once?

the locking rules here are a bit confusing. (I didn't have my morning coffee yet).

	-ss

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  reply	other threads:[~2016-06-03  1:00 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
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 [this message]
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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