From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from hqnvemgate24.nvidia.com ([216.228.121.143]:11367 "EHLO hqnvemgate24.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726046AbgB1XIh (ORCPT ); Fri, 28 Feb 2020 18:08:37 -0500 Subject: Re: [RFC v1 1/2] mm/gup: fixup for 9947ea2c1e608e32 "mm/gup: track FOLL_PIN pages" References: <20200228154322.329228-1-imbrenda@linux.ibm.com> <20200228154322.329228-3-imbrenda@linux.ibm.com> From: John Hubbard Message-ID: Date: Fri, 28 Feb 2020 15:08:35 -0800 MIME-Version: 1.0 In-Reply-To: <20200228154322.329228-3-imbrenda@linux.ibm.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-s390-owner@vger.kernel.org List-ID: To: Claudio Imbrenda , linux-next@vger.kernel.org, akpm@linux-foundation.org Cc: borntraeger@de.ibm.com, david@redhat.com, aarcange@redhat.com, linux-mm@kvack.org, frankja@linux.ibm.com, sfr@canb.auug.org.au, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, Jan Kara , "Kirill A. Shutemov" On 2/28/20 7:43 AM, Claudio Imbrenda wrote: > In case pin fails, we need to unpin, a simple put_page will not be enough > > Signed-off-by: Claudio Imbrenda > --- > mm/gup.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/mm/gup.c b/mm/gup.c > index f589299b0d4a..0b9a806898f3 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -2134,7 +2134,10 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end, > goto pte_unmap; > > if (unlikely(pte_val(pte) != pte_val(*ptep))) { > - put_page(head); > + if (flags & FOLL_GET) > + put_page(head); > + else if (flags & FOLL_PIN) > + unpin_user_page(head); Hi Claudio, Instead, I think that should actually be: put_compound_head(page, 1, flags); which does a bit more (bug checks and /proc/vmstat instrumentation) than your diff, but has the same basic idea: call the right "put" function. ...oh, actually, I see you have the commit hash in the subject line. Instead, it should be in the commit description. Let's maybe change the subject line to approx: mm/gup: Fix a missing put_compound_head() call in gup_pte_range() And the write up...how about something like this, if you like it: try_grab_compound_head() must be undone via put_compound_head(), not put_page(). This was missed in the original implementation of the gup/dma tracking patch, so fix it now. Fixes: 0ea2781c3de4 ("mm/gup: track FOLL_PIN pages") (Aside: I'm using the linux-next commit hash. How does one get the correct hash before it goes to mainline? I guess maintainer scripts fix all those up?) It's also good to Cc some reviewers in case I'm overlooking something, so I'm adding Jan and Kirill. thanks, -- John Hubbard NVIDIA > goto pte_unmap; > } > >