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Fri, 9 Sep 2022 15:52:31 GMT Received: from d06av24.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id A07D142045; Fri, 9 Sep 2022 15:52:31 +0000 (GMT) Received: from d06av24.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 9260642041; Fri, 9 Sep 2022 15:52:30 +0000 (GMT) Received: from [9.145.83.17] (unknown [9.145.83.17]) by d06av24.portsmouth.uk.ibm.com (Postfix) with ESMTP; Fri, 9 Sep 2022 15:52:30 +0000 (GMT) Message-ID: <3faf8347-5062-4d8d-0360-c23ac5c525b3@linux.ibm.com> Date: Fri, 9 Sep 2022 17:52:30 +0200 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.2.1 Subject: Re: [RFC PATCH RESEND 10/28] mm/mmap: mark VMAs as locked in vma_adjust Content-Language: fr To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, michel@lespinasse.org, jglisse@google.com, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, mgorman@suse.de, dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com, peterz@infradead.org, laurent.dufour@fr.ibm.com, paulmck@kernel.org, luto@kernel.org, songliubraving@fb.com, peterx@redhat.com, david@redhat.com, dhowells@redhat.com, hughd@google.com, bigeasy@linutronix.de, kent.overstreet@linux.dev, rientjes@google.com, axelrasmussen@google.com, joelaf@google.com, minchan@google.com, kernel-team@android.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, x86@kernel.org, linux-kernel@vger.kernel.org References: <20220901173516.702122-1-surenb@google.com> <20220901173516.702122-11-surenb@google.com> From: Laurent Dufour In-Reply-To: Content-Type: text/plain; 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dkim=pass header.d=ibm.com header.s=pp1 header.b=OhgNZ53e; dmarc=pass (policy=none) header.from=ibm.com; spf=pass (imf11.hostedemail.com: domain of ldufour@linux.ibm.com designates 148.163.158.5 as permitted sender) smtp.mailfrom=ldufour@linux.ibm.com X-Rspamd-Server: rspam12 X-HE-Tag: 1662738766-234175 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000005, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Le 09/09/2022 à 02:51, Suren Baghdasaryan a écrit : > On Tue, Sep 6, 2022 at 8:35 AM Laurent Dufour wrote: >> >> Le 01/09/2022 à 19:34, Suren Baghdasaryan a écrit : >>> vma_adjust modifies a VMA and possibly its neighbors. Mark them as locked >>> before making the modifications. >>> >>> Signed-off-by: Suren Baghdasaryan >>> --- >>> mm/mmap.c | 11 ++++++++++- >>> 1 file changed, 10 insertions(+), 1 deletion(-) >>> >>> diff --git a/mm/mmap.c b/mm/mmap.c >>> index f89c9b058105..ed58cf0689b2 100644 >>> --- a/mm/mmap.c >>> +++ b/mm/mmap.c >>> @@ -710,6 +710,10 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start, >>> long adjust_next = 0; >>> int remove_next = 0; >>> >>> + vma_mark_locked(vma); >>> + if (next) >>> + vma_mark_locked(next); >>> + >> >> I was wondering if the VMAs insert and expand should be locked too. >> >> For expand, I can't see any valid reason, but for insert, I'm puzzled. >> I would think that it is better to lock the VMA to be inserted but I can't >> really justify that. >> >> It may be nice to detail why this is not need to lock insert and expand here. > > 'expand' is always locked before it's passed to __vma_adjust() by > vma_merge(). It has to be locked before we decide "Can it merge with > the predecessor?" here > https://elixir.bootlin.com/linux/latest/source/mm/mmap.c#L1201 because > a change in VMA can affect that decision. I spent many hours tracking > the issue caused by not locking the VMA before making this decision. > It might be good to add a comment about this... > > AFAIKT 'insert' is only used by __split_vma() and it's always a brand > new VMA which is not yet linked into mm->mmap. Any reason > __vma_adjust() should lock it? No, I think that's good this way. > >> >>> if (next && !insert) { >>> struct vm_area_struct *exporter = NULL, *importer = NULL; >>> >>> @@ -754,8 +758,11 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start, >>> * If next doesn't have anon_vma, import from vma after >>> * next, if the vma overlaps with it. >>> */ >>> - if (remove_next == 2 && !next->anon_vma) >>> + if (remove_next == 2 && !next->anon_vma) { >>> exporter = next->vm_next; >>> + if (exporter) >>> + vma_mark_locked(exporter); >>> + } >>> >>> } else if (end > next->vm_start) { >>> /* >>> @@ -931,6 +938,8 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start, >>> * "vma->vm_next" gap must be updated. >>> */ >>> next = vma->vm_next; >>> + if (next) >>> + vma_mark_locked(next); >>> } else { >>> /* >>> * For the scope of the comment "next" and >> >> -- >> To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com. >>