From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f198.google.com (mail-pf0-f198.google.com [209.85.192.198]) by kanga.kvack.org (Postfix) with ESMTP id E014A6B007E for ; Thu, 2 Jun 2016 21:29:24 -0400 (EDT) Received: by mail-pf0-f198.google.com with SMTP id c84so83411653pfc.3 for ; Thu, 02 Jun 2016 18:29:24 -0700 (PDT) Received: from mail-pa0-x243.google.com (mail-pa0-x243.google.com. [2607:f8b0:400e:c03::243]) by mx.google.com with ESMTPS id a4si1578638pfb.189.2016.06.02.18.29.23 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 02 Jun 2016 18:29:24 -0700 (PDT) Received: by mail-pa0-x243.google.com with SMTP id x1so4531768pav.1 for ; Thu, 02 Jun 2016 18:29:23 -0700 (PDT) Date: Fri, 3 Jun 2016 10:29:19 +0900 From: Sergey Senozhatsky Subject: Re: [linux-next: Tree for Jun 1] __khugepaged_exit rwsem_down_write_failed lockup Message-ID: <20160603012919.GB464@swordfish> References: <20160601131122.7dbb0a65@canb.auug.org.au> <20160602014835.GA635@swordfish> <0c47a3a0-5530-b257-1c1f-28ed44ba97e6@suse.cz> <20160602185856.GA3854@debian> <20160603010036.GA464@swordfish> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160603010036.GA464@swordfish> Sender: owner-linux-mm@kvack.org List-ID: To: Sergey Senozhatsky Cc: Ebru Akagunduz , Vlastimil Babka , Andrew Morton , Michal Hocko , "Kirill A. Shutemov" , Stephen Rothwell , Andrea Arcangeli , Rik van Riel , linux-mm@kvack.org, linux-next@vger.kernel.org, linux-kernel@vger.kernel.org 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 > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org