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[209.132.183.28]) by mx.google.com with ESMTPS id s7si24705757qkc.12.2019.07.25.01.14.18 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 25 Jul 2019 01:14:18 -0700 (PDT) Received-SPF: pass (google.com: domain of oleg@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of oleg@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=oleg@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 64CA485546; Thu, 25 Jul 2019 08:14:17 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.136]) by smtp.corp.redhat.com (Postfix) with SMTP id 5028B600C4; Thu, 25 Jul 2019 08:14:15 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Thu, 25 Jul 2019 10:14:17 +0200 (CEST) Date: Thu, 25 Jul 2019 10:14:14 +0200 From: Oleg Nesterov To: Song Liu Cc: lkml , Linux-MM , Andrew Morton , "matthew.wilcox@oracle.com" , "kirill.shutemov@linux.intel.com" , "peterz@infradead.org" , "rostedt@goodmis.org" , Kernel Team , "william.kucharski@oracle.com" Subject: Re: [PATCH v8 2/4] uprobe: use original page when all uprobes are removed Message-ID: <20190725081414.GB4707@redhat.com> References: <20190724083600.832091-1-songliubraving@fb.com> <20190724083600.832091-3-songliubraving@fb.com> <20190724113711.GE21599@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Thu, 25 Jul 2019 08:14:17 +0000 (UTC) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 07/24, Song Liu wrote: > > > > On Jul 24, 2019, at 4:37 AM, Oleg Nesterov wrote: > > > > On 07/24, Song Liu wrote: > >> > >> lock_page(old_page); > >> @@ -177,15 +180,24 @@ static int __replace_page(struct vm_area_struct *vma, unsigned long addr, > >> mmu_notifier_invalidate_range_start(&range); > >> err = -EAGAIN; > >> if (!page_vma_mapped_walk(&pvmw)) { > >> - mem_cgroup_cancel_charge(new_page, memcg, false); > >> + if (!orig) > >> + mem_cgroup_cancel_charge(new_page, memcg, false); > >> goto unlock; > >> } > >> VM_BUG_ON_PAGE(addr != pvmw.address, old_page); > >> > >> get_page(new_page); > >> - page_add_new_anon_rmap(new_page, vma, addr, false); > >> - mem_cgroup_commit_charge(new_page, memcg, false, false); > >> - lru_cache_add_active_or_unevictable(new_page, vma); > >> + if (orig) { > >> + lock_page(new_page); /* for page_add_file_rmap() */ > >> + page_add_file_rmap(new_page, false); > > > > > > Shouldn't we re-check new_page->mapping after lock_page() ? Or we can't > > race with truncate? > > We can't race with truncate, because the file is open as binary and > protected with DENYWRITE (ETXTBSY). No. Yes, deny_write_access() protects mm->exe_file, but not the dynamic libraries or other files which can be mmaped. > > and I am worried this code can try to lock the same page twice... > > Say, the probed application does MADV_DONTNEED and then writes "int3" > > into vma->vm_file at the same address to fool verify_opcode(). > > > > Do you mean the case where old_page == new_page? Yes, > I think this won't > happen, because in uprobe_write_opcode() we only do orig_page for > !is_register case. See above. !is_register doesn't necessarily mean the original page was previously cow'ed. And even if it was cow'ed, MADV_DONTNEED can restore the original mapping. Oleg.