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Fri, 9 Sep 2022 13:27:32 GMT Received: from d06av24.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 22BB742045; Fri, 9 Sep 2022 13:27:32 +0000 (GMT) Received: from d06av24.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id A234742041; Fri, 9 Sep 2022 13:27:30 +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 13:27:30 +0000 (GMT) Message-ID: Date: Fri, 9 Sep 2022 15:27:30 +0200 MIME-Version: 1.0 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 07/28] kernel/fork: mark VMAs as locked before copying pages during fork Content-Language: fr To: Suren Baghdasaryan References: <20220901173516.702122-1-surenb@google.com> <20220901173516.702122-8-surenb@google.com> From: Laurent Dufour In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: AKENId9QRksp4m3H-lE_THCmMHniIzD8 X-Proofpoint-GUID: CFGeekGWSpIQRCVQ4AE9GyYndL5KhzSD X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.895,Hydra:6.0.528,FMLib:17.11.122.1 definitions=2022-09-09_08,2022-09-09_01,2022-06-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxscore=0 suspectscore=0 adultscore=0 clxscore=1015 priorityscore=1501 mlxlogscore=999 spamscore=0 phishscore=0 impostorscore=0 bulkscore=0 lowpriorityscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2207270000 definitions=main-2209090045 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: michel@lespinasse.org, joelaf@google.com, songliubraving@fb.com, mhocko@suse.com, david@redhat.com, peterz@infradead.org, bigeasy@linutronix.de, peterx@redhat.com, dhowells@redhat.com, linux-mm@kvack.org, jglisse@google.com, dave@stgolabs.net, minchan@google.com, x86@kernel.org, hughd@google.com, willy@infradead.org, laurent.dufour@fr.ibm.com, mgorman@suse.de, rientjes@google.com, axelrasmussen@google.com, kernel-team@android.com, paulmck@kernel.org, liam.howlett@oracle.com, luto@kernel.org, vbabka@suse.cz, linux-arm-kernel@lists.infradead.org, kent.overstreet@linux.dev, linux-kernel@vger.kernel.org, hannes@cmpxchg.org, akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Le 09/09/2022 à 01:57, Suren Baghdasaryan a écrit : > On Tue, Sep 6, 2022 at 7:38 AM Laurent Dufour wrote: >> >> Le 01/09/2022 à 19:34, Suren Baghdasaryan a écrit : >>> Protect VMAs from concurrent page fault handler while performing >>> copy_page_range for VMAs having VM_WIPEONFORK flag set. >> >> I'm wondering why is that necessary. >> The copied mm is write locked, and the destination one is not reachable. >> If any other readers are using the VMA, this is only for page fault handling. > > Correct, this is done to prevent page faulting in the VMA being > duplicated. I assume we want to prevent the pages in that VMA from > changing when we are calling copy_page_range(). Am I wrong? If a page is faulted while copy_page_range() is in progress, the page may not be backed on the child side (PTE lock should protect the copy, isn't it). Is that a real problem? It will be backed later if accessed on the child side. Maybe the per process pages accounting could be incorrect... > >> I should have miss something because I can't see any need to mark the lock >> VMA here. >> >>> Signed-off-by: Suren Baghdasaryan >>> --- >>> kernel/fork.c | 4 +++- >>> 1 file changed, 3 insertions(+), 1 deletion(-) >>> >>> diff --git a/kernel/fork.c b/kernel/fork.c >>> index bfab31ecd11e..1872ad549fed 100644 >>> --- a/kernel/fork.c >>> +++ b/kernel/fork.c >>> @@ -709,8 +709,10 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm, >>> rb_parent = &tmp->vm_rb; >>> >>> mm->map_count++; >>> - if (!(tmp->vm_flags & VM_WIPEONFORK)) >>> + if (!(tmp->vm_flags & VM_WIPEONFORK)) { >>> + vma_mark_locked(mpnt); >>> retval = copy_page_range(tmp, mpnt); >>> + } >>> >>> if (tmp->vm_ops && tmp->vm_ops->open) >>> tmp->vm_ops->open(tmp); >>