From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Ebru Akagunduz <ebru.akagunduz@gmail.com>,
Vlastimil Babka <vbabka@suse.cz>,
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 10:29:19 +0900 [thread overview]
Message-ID: <20160603012919.GB464@swordfish> (raw)
In-Reply-To: <20160603010036.GA464@swordfish>
On (06/03/16 10:00), Sergey Senozhatsky wrote:
> 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);
> : ^^^^^^^^^
oh... it's in a loop
for (_address = address; _address < address + HPAGE_PMD_NR*PAGE_SIZE;
pte++, _address += PAGE_SIZE) {
ret = do_swap_page()
if (ret & VM_FAULT_RETRY) {
down_read(&mm->mmap_sem);
^^^^^^^^^
...
}
}
so there can be multiple sem->count++ in __collapse_huge_page_swapin(),
and you don't know how many sem->count-- you need to do later? is this
correct or am I hallucinating?
-ss
> : 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 1:29 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
2016-06-03 1:29 ` Sergey Senozhatsky [this message]
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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