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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 2AA9FC55174 for ; Sat, 8 Aug 2026 03:39:33 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id E47B36B008C; Fri, 7 Aug 2026 23:39:31 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id DF8686B0092; Fri, 7 Aug 2026 23:39:31 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id CE78B6B0093; Fri, 7 Aug 2026 23:39:31 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id A88186B008C for ; Fri, 7 Aug 2026 23:39:31 -0400 (EDT) Received: from smtpin08.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay04.hostedemail.com (Postfix) with ESMTP id ADA4B1A027F for ; Sat, 8 Aug 2026 03:39:29 +0000 (UTC) X-FDA: 85076697258.08.D02F998 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf10.hostedemail.com (Postfix) with ESMTP id 3921BC000A for ; Sat, 8 Aug 2026 03:39:26 +0000 (UTC) Authentication-Results: imf10.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=Yo8nL7sX; spf=pass (imf10.hostedemail.com: domain of willy@infradead.org designates 90.155.50.34 as permitted sender) smtp.mailfrom=willy@infradead.org; dmarc=pass (policy=none) header.from=infradead.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1786160366; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=zPdvXze8eJ+ip1RN4T5sK8ZVGUl8K7CRCIHKK0OEMsY=; b=gMSAnS5IY9vQaYy6uOfjxJ56t0fudJp+SEY4ULUWvJkkHi0tWAofvN523cay2xleuH74sK YRWB/XRJWSwQ5APywbWd4tKLyhmyl97I0SAwGKJ34wy6p8WBoyaUodGzYxPjWhVsGlx4pI z7BRXRDxUfXUnd3O0SEvi5lTvGkP8j8= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1786160366; b=MDEdLhvWp4+iQf7UrLmuac+YzMwLCp0UMCVIjgM/WA5z4SK0iC2aeAAWZcw6b/yhyASkHz Yb8haTgiquiTd0PSDxh9peSbN8/AT2dbHYIB0Gmlrqn1dvdMx2oQ86dn3ngt0Wazo0OOSx aWhXVD1jDW3XjPIQ7yzFQp3/A6NHQRY= ARC-Authentication-Results: i=1; imf10.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=Yo8nL7sX; spf=pass (imf10.hostedemail.com: domain of willy@infradead.org designates 90.155.50.34 as permitted sender) smtp.mailfrom=willy@infradead.org; dmarc=pass (policy=none) header.from=infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=zPdvXze8eJ+ip1RN4T5sK8ZVGUl8K7CRCIHKK0OEMsY=; b=Yo8nL7sXT8DRH38MZOCw9KMwkr FAGRqZvulhAtUjnuFQ/xUT7VCJP3ZAz6pmjW+4saebDg7NiH/RsA9+0Kpt/PWmkioG1+G35+7fCoS WxDFIETAP35cQ+2y3/Mi7493pxT5koC5/6xxcZJMI/Gc0ch+zQoaaHbikgQIzLBF5RmOoVYF4Ld1G EZApA0iQw3Ox2+EXHHsaLEdwbfC+tCEekT1PTPToUC3n6ZQaY5pBoQseiPCWf0LoGF4r42Xi5whKf 5yH6lMKcuUhcIDYN9K4tRjP+3czgzJzw/I1lDa9qR8GKtcqdU6NGeWAY9a2d37wm7kbmtMK4OxqxX hm2Im+OQ==; Received: from willy by casper.infradead.org with local (Exim 4.99.1 #2 (Red Hat Linux)) id 1wsVcI-0000000189D-1P0D; Sat, 08 Aug 2026 01:13:14 +0000 Date: Sat, 8 Aug 2026 02:12:50 +0100 From: Matthew Wilcox To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, dave.hansen@linux.intel.com, Liam.Howlett@oracle.com, ljs@kernel.org, david@kernel.org, shakeel.butt@linux.dev, vbabka@kernel.org, jannh@google.com, aliceryhl@google.com, arve@android.com, cmllamas@google.com, christian@brauner.io, tkjos@android.com, dsahern@kernel.org, davem@davemloft.net, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, netdev@vger.kernel.org Subject: Re: [PATCH v4 1/5] mm: Make per-VMA locks available universally Message-ID: References: <20260806200548.3124802-1-surenb@google.com> <20260806200548.3124802-2-surenb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260806200548.3124802-2-surenb@google.com> X-Rspamd-Queue-Id: 3921BC000A X-Rspamd-Server: rspam10 X-Rspam-User: X-Stat-Signature: r6rrpaczpf8dyqkafbh5a4hkd1fnze34 X-HE-Tag: 1786160366-801226 X-HE-Meta: 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 gAVcUqlN IkF9uT09YTftP3ose2ChZXpE06oSWqf+qOrTUeKHRAz8ZDWMilNX6eHeunwo5+4rlX/mEafFWK1E1QzACRv4vSxBi5Yuzuou/99j4OelE6rSQ+gu1VLvrWWR1bMDtUIEG8jHSpstqQuNreI8S9Wc3icc+jQ3LDBAWNBVeIsOProd99QUxsf3zY8qIOCgXdNFv7JtdCTduJDIn6PBucZ5rNuxcA98p0cFROjLaPvstae6b0kk76+V7xVCcgcWJWnUX+ATOOYXQgDzZq6qv5GPpheWoA/JLsZAiO20FZl0ZcplBE+RzJwfjmRZuxDmybVNXYWdX Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Aug 06, 2026 at 01:05:44PM -0700, Suren Baghdasaryan wrote: > +++ b/kernel/bpf/stackmap.c > @@ -272,13 +272,8 @@ struct stack_map_vma_lock { > /* > * Acquire a stable read-side reference on the VMA covering @ip. > * > - * With CONFIG_PER_VMA_LOCK=y this returns a VMA with its per-VMA read > - * lock held and mmap_lock dropped, so the caller may sleep. > - * > - * With CONFIG_PER_VMA_LOCK=n it returns a VMA with mmap_lock still > - * held; the caller must snapshot any fields it needs and pin vm_file > - * with get_file() before stack_map_unlock_vma() drops mmap_lock, as > - * the VMA may be split, merged, or freed after that. > + * This returns a VMA with its per-VMA read lock held and mmap_lock > + * dropped, so the caller may sleep. I don't know if BPF is compatible with !MMU or not, but the comment is inconsistent with the code. How about: * On NOMMU configurations, returns with the mmap_lock held. If the MMU * is enabled, the per-VMA lock will be held instead. The lock * should be released with stack_map_unlock_vma() which will release the * appropriate lock. Once the lock is released, the VMA may be freed. > * Returns NULL on failure, in which case no lock is held. > */ > @@ -288,7 +283,6 @@ stack_map_lock_vma(struct stack_map_vma_lock *lock, unsigned long ip) > struct mm_struct *mm = lock->mm; > struct vm_area_struct *vma; > > - /* noop under !CONFIG_PER_VMA_LOCK */ > vma = lock_vma_under_rcu(mm, ip); > if (vma) { > lock->vma = vma; > @@ -308,21 +302,20 @@ stack_map_lock_vma(struct stack_map_vma_lock *lock, unsigned long ip) > return NULL; > } > > -#ifdef CONFIG_PER_VMA_LOCK > +#ifdef CONFIG_MMU > if (!vma_start_read_locked(vma)) { > mmap_read_unlock(mm); > return NULL; > } > mmap_read_unlock(mm); > #endif > - > lock->vma = vma; > return vma; > }