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
next prev parent reply other threads:[~2016-06-03 1:01 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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