From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 95FBDC3DA78 for ; Tue, 17 Jan 2023 15:15:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232280AbjAQPPM (ORCPT ); Tue, 17 Jan 2023 10:15:12 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52026 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231656AbjAQPPH (ORCPT ); Tue, 17 Jan 2023 10:15:07 -0500 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 597027ABC for ; Tue, 17 Jan 2023 07:15:06 -0800 (PST) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 11F6C6892C; Tue, 17 Jan 2023 15:15:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1673968505; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=nBlegFKztT0lzY7LSYGJmo+x7Ufu6srgtkLxKq1Himw=; b=dhfrMcpLa1spzObMQUrhKH+kFBryqMQH550Qvc2LxXW9s9KzGwXe9gHdEBZsFXUfvzztwG VjO3QQNentMSULFa+pXW+jm3VKwc4k11cgXRsSJAGHBeBpR61TVwLecZeZ94BBc5prFJ9P z7y+AUgxM0Nry/3jgMBaDIHRKaQKJj0= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id DAD901390C; Tue, 17 Jan 2023 15:15:04 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id b6JdNXi7xmMQRQAAMHmgww (envelope-from ); Tue, 17 Jan 2023 15:15:04 +0000 Date: Tue, 17 Jan 2023 16:15:04 +0100 From: Michal Hocko To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, michel@lespinasse.org, jglisse@google.com, vbabka@suse.cz, hannes@cmpxchg.org, mgorman@techsingularity.net, dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com, peterz@infradead.org, ldufour@linux.ibm.com, 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, punit.agrawal@bytedance.com, lstoakes@gmail.com, peterjung1337@gmail.com, rientjes@google.com, axelrasmussen@google.com, joelaf@google.com, minchan@google.com, jannh@google.com, shakeelb@google.com, tatashin@google.com, edumazet@google.com, gthelen@google.com, gurua@google.com, arjunroy@google.com, soheil@google.com, hughlynch@google.com, leewalsh@google.com, posk@google.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, x86@kernel.org, linux-kernel@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH 13/41] mm: introduce vma->vm_flags modifier functions Message-ID: References: <20230109205336.3665937-1-surenb@google.com> <20230109205336.3665937-14-surenb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 17-01-23 16:09:03, Michal Hocko wrote: > On Mon 09-01-23 12:53:08, Suren Baghdasaryan wrote: > > To keep vma locking correctness when vm_flags are modified, add modifier > > functions to be used whenever flags are updated. > > > > Signed-off-by: Suren Baghdasaryan > > --- > > include/linux/mm.h | 38 ++++++++++++++++++++++++++++++++++++++ > > include/linux/mm_types.h | 8 +++++++- > > 2 files changed, 45 insertions(+), 1 deletion(-) > > > > diff --git a/include/linux/mm.h b/include/linux/mm.h > > index ec2c4c227d51..35cf0a6cbcc2 100644 > > --- a/include/linux/mm.h > > +++ b/include/linux/mm.h > > @@ -702,6 +702,44 @@ static inline void vma_init(struct vm_area_struct *vma, struct mm_struct *mm) > > vma_init_lock(vma); > > } > > > > +/* Use when VMA is not part of the VMA tree and needs no locking */ > > +static inline > > +void init_vm_flags(struct vm_area_struct *vma, unsigned long flags) > > +{ > > + WRITE_ONCE(vma->vm_flags, flags); > > +} > > Why do we need WRITE_ONCE here? Isn't vma invisible during its > initialization? > > > + > > +/* Use when VMA is part of the VMA tree and needs appropriate locking */ > > +static inline > > +void reset_vm_flags(struct vm_area_struct *vma, unsigned long flags) > > +{ > > + vma_write_lock(vma); > > + init_vm_flags(vma, flags); > > +} > > + > > +static inline > > +void set_vm_flags(struct vm_area_struct *vma, unsigned long flags) > > +{ > > + vma_write_lock(vma); > > + vma->vm_flags |= flags; > > +} > > + > > +static inline > > +void clear_vm_flags(struct vm_area_struct *vma, unsigned long flags) > > +{ > > + vma_write_lock(vma); > > + vma->vm_flags &= ~flags; > > +} > > + > > +static inline > > +void mod_vm_flags(struct vm_area_struct *vma, > > + unsigned long set, unsigned long clear) > > +{ > > + vma_write_lock(vma); > > + vma->vm_flags |= set; > > + vma->vm_flags &= ~clear; > > +} > > + > > This is rather unusual pattern. There is no note about locking involved > in the naming and also why is the locking part of this interface in the > first place? I can see reason for access functions to actually check for > lock asserts. OK, it took me a while but it is clear to me now. The confusion comes from the naming vma_write_lock is no a lock in its usual terms. It is more of a vma_mark_modified with side effects to read locking which is a real lock. With that it makes more sense to have this done in these helpers rather than requiring all users to keep this subtletly in mind. -- Michal Hocko SUSE Labs