From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.223.131]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D00C0274FEB for ; Tue, 5 Aug 2025 14:18:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=195.135.223.131 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754403535; cv=none; b=j3woGhX17TKY6eV+xqVre64zaImOjAFsH7QIBMbNvLZZTuvI3goYoARUtchBMwmwjiSUgjm+L/Bed/InXkGx+jCgk7+K/E5YKCMwM14kUKWkSUOAje5QMQlDszPv6LvMKDG4EwenDzYYHGmWjlJEe9267F+ApOIW35lnlIIfj/0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754403535; c=relaxed/simple; bh=8aRcbWkNJ7XJB7HhT/RC3DT8xiYVHSKOLO2NPWxyEFk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=pN67p7bV99DsZ2bQo6fGNXiAt4bMAEECtYN6m/BxJfI7zqGwgSAskncHnIJyu2W+HaOyQZvxHaaM5uPDvNXEP7YpeiGgEw4UCV2MJuZ2H6V+PxPu43em/aZJnFAhbOrrPUD1zPnsg2q0MyNmMx1pzDbtrUgw17PeMxtdRDHw68E= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz; spf=pass smtp.mailfrom=suse.cz; dkim=pass (1024-bit key) header.d=suse.cz header.i=@suse.cz header.b=JLEiwTWg; dkim=permerror (0-bit key) header.d=suse.cz header.i=@suse.cz header.b=15OpfyJo; dkim=pass (1024-bit key) header.d=suse.cz header.i=@suse.cz header.b=zDiNZGJ5; dkim=permerror (0-bit key) header.d=suse.cz header.i=@suse.cz header.b=ZnbvifoH; arc=none smtp.client-ip=195.135.223.131 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=suse.cz Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=suse.cz header.i=@suse.cz header.b="JLEiwTWg"; dkim=permerror (0-bit key) header.d=suse.cz header.i=@suse.cz header.b="15OpfyJo"; dkim=pass (1024-bit key) header.d=suse.cz header.i=@suse.cz header.b="zDiNZGJ5"; dkim=permerror (0-bit key) header.d=suse.cz header.i=@suse.cz header.b="ZnbvifoH" Received: from imap1.dmz-prg2.suse.org (unknown [10.150.64.97]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id DB6CE1F38A; Tue, 5 Aug 2025 14:18:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1754403531; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=+NfTJO6QExB/AjtZCsMzDvrCWnZLiopnMrmlLDf3JbE=; b=JLEiwTWgrN3FMXG6fIc7sMoJCxq1EVPmn0gw60A48lFseG+7pgp16TK0QsWp2cyVPSlB/d Ax+Gw0JlK4Ic1I5p9wroVK7OffPuUuzWkwRIAtIjjJCgaMcdqyBW6T9hWmecarQgR9mpQE OcoOcLoqzQ/JdIiyuaVHAe7bXMGe0cY= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1754403531; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=+NfTJO6QExB/AjtZCsMzDvrCWnZLiopnMrmlLDf3JbE=; b=15OpfyJoyk2taAkgIC4Xv+OOtyhWW4yD2jIA+HdaA0B9fKtQ5TD5UCTC0igqFmqQ3E8Gz+ 59OI7CE+fPo/VRDQ== Authentication-Results: smtp-out2.suse.de; none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1754403530; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=+NfTJO6QExB/AjtZCsMzDvrCWnZLiopnMrmlLDf3JbE=; b=zDiNZGJ5si2mcehmfw2uKJsVv/5QwnJ6f3tNpjsLAoeQmqBlltQNalA9bop2V2mU6urcLB 1rnepXmjAR41zGBOEEQSGv/ckndF0/HNZADa6bItMJME+ydlyKB7WT+CUIj3PF6Hk3a+3d hydmdVEkZp/7sEij6hxG7BWqmmO6fDs= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1754403530; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=+NfTJO6QExB/AjtZCsMzDvrCWnZLiopnMrmlLDf3JbE=; b=ZnbvifoHF0Ve/E4VFWtrLfAQSaYUTFoeM8xoPnpU01Q7Mo4yP0G3GwG2rcPBIw0ZSkljNF 2gAHxNsZHZZYPrDQ== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id D0D8513A50; Tue, 5 Aug 2025 14:18:49 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id ysP5MMkSkmh2LwAAD6G6ig (envelope-from ); Tue, 05 Aug 2025 14:18:49 +0000 Message-ID: Date: Tue, 5 Aug 2025 16:20:47 +0200 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 3/3] fs/proc/task_mmu: execute PROCMAP_QUERY ioctl under per-vma locks To: Suren Baghdasaryan , akpm@linux-foundation.org Cc: Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, david@redhat.com, peterx@redhat.com, jannh@google.com, hannes@cmpxchg.org, mhocko@kernel.org, paulmck@kernel.org, shuah@kernel.org, adobriyan@gmail.com, brauner@kernel.org, josef@toxicpanda.com, yebin10@huawei.com, linux@weissschuh.net, willy@infradead.org, osalvador@suse.de, andrii@kernel.org, ryan.roberts@arm.com, christophe.leroy@csgroup.eu, tjmercier@google.com, kaleshsingh@google.com, aha310510@gmail.com, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org References: <20250804231552.1217132-1-surenb@google.com> <20250804231552.1217132-4-surenb@google.com> From: Vlastimil Babka Content-Language: en-US In-Reply-To: <20250804231552.1217132-4-surenb@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-0.999]; MIME_GOOD(-0.10)[text/plain]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; MIME_TRACE(0.00)[0:+]; FUZZY_RATELIMITED(0.00)[rspamd.com]; TO_DN_SOME(0.00)[]; RCPT_COUNT_TWELVE(0.00)[28]; RCVD_TLS_ALL(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[oracle.com,redhat.com,google.com,cmpxchg.org,kernel.org,gmail.com,toxicpanda.com,huawei.com,weissschuh.net,infradead.org,suse.de,arm.com,csgroup.eu,vger.kernel.org,kvack.org]; R_RATELIMIT(0.00)[to_ip_from(RLqwhhqik4qyk5i1fk54co8f1o)]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,suse.cz:mid] X-Spam-Flag: NO X-Spam-Level: X-Spam-Score: -4.30 On 8/5/25 1:15 AM, Suren Baghdasaryan wrote: > Utilize per-vma locks to stabilize vma after lookup without taking > mmap_lock during PROCMAP_QUERY ioctl execution. If vma lock is > contended, we fall back to mmap_lock but take it only momentarily > to lock the vma and release the mmap_lock. In a very unlikely case > of vm_refcnt overflow, this fall back path will fail and ioctl is > done under mmap_lock protection. > > This change is designed to reduce mmap_lock contention and prevent > PROCMAP_QUERY ioctl calls from blocking address space updates. > > Signed-off-by: Suren Baghdasaryan > --- > fs/proc/task_mmu.c | 81 +++++++++++++++++++++++++++++++++++++--------- > 1 file changed, 65 insertions(+), 16 deletions(-) > > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > index 843577aa7a32..1d06ecdbef6f 100644 > --- a/fs/proc/task_mmu.c > +++ b/fs/proc/task_mmu.c > @@ -517,28 +517,78 @@ static int pid_maps_open(struct inode *inode, struct file *file) > PROCMAP_QUERY_VMA_FLAGS \ > ) > > -static int query_vma_setup(struct mm_struct *mm) > +#ifdef CONFIG_PER_VMA_LOCK > + > +static int query_vma_setup(struct proc_maps_locking_ctx *lock_ctx) > { > - return mmap_read_lock_killable(mm); > + lock_ctx->locked_vma = NULL; > + lock_ctx->mmap_locked = false; > + > + return 0; > } > > -static void query_vma_teardown(struct mm_struct *mm, struct vm_area_struct *vma) > +static void query_vma_teardown(struct proc_maps_locking_ctx *lock_ctx) > { > - mmap_read_unlock(mm); > + if (lock_ctx->mmap_locked) > + mmap_read_unlock(lock_ctx->mm); > + else > + unlock_vma(lock_ctx); > } > > -static struct vm_area_struct *query_vma_find_by_addr(struct mm_struct *mm, unsigned long addr) > +static struct vm_area_struct *query_vma_find_by_addr(struct proc_maps_locking_ctx *lock_ctx, > + unsigned long addr) > { > - return find_vma(mm, addr); > + struct vm_area_struct *vma; > + struct vma_iterator vmi; > Hm I think we can reach here with lock_ctx->mmap_locked being true via "goto next_vma" in query_matching_vma(). In that case we should just "return find_vma()" and doing the below is wrong, no? > + unlock_vma(lock_ctx); > + rcu_read_lock(); > + vma_iter_init(&vmi, lock_ctx->mm, addr); > + vma = lock_next_vma(lock_ctx->mm, &vmi, addr); > + rcu_read_unlock(); > + > + if (!IS_ERR_OR_NULL(vma)) { > + lock_ctx->locked_vma = vma; > + } else if (PTR_ERR(vma) == -EAGAIN) { > + /* Fallback to mmap_lock on vma->vm_refcnt overflow */ > + mmap_read_lock(lock_ctx->mm); > + vma = find_vma(lock_ctx->mm, addr); > + lock_ctx->mmap_locked = true; > + } > + > + return vma; > } >