From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-189.mta0.migadu.com (out-189.mta0.migadu.com [91.218.175.189]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 682401991B1 for ; Thu, 5 Sep 2024 12:07:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.189 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725538039; cv=none; b=r/hzchajhxt1ajrj45/x/RSpn0yUNeqPJ6Sp0lOa9ABGxBUI6wEXDaBLHZLP49Bhma03YtKaeZx7eRrW91rlbftLY6Kk9FDM9MQSqTYETfiRf04zSQicajQOlS7Se6ImhskesWjUScps3wkUA281UdkAc+k6OXgnSK2RZhq3QJw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725538039; c=relaxed/simple; bh=LwXcqXwqi86LwgQpkvbJ6aG6gSxvOL+s5uKNn9S/kVY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=A1yuulU02gnlxR1HAQjU8iQZ0Gbe3MoXNnI16X2UyHaRO62b3lP7/VRq1k9xyFiumvLn0mgxcI3R+k2ptrCVUQunT+itLhJJPMJq3tewdqjlUacG6QoSp0br6kVbjMD23h6ve+xof/KBnWYir9ePDllLSpNwrnwiV2vJeOkZRAU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=JFyaLw6V; arc=none smtp.client-ip=91.218.175.189 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="JFyaLw6V" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1725538034; h=from:from: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:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=HPUN+LftKuZr9srXj9cbq7IzfWnEz1/nVI7Ulrm9sGw=; b=JFyaLw6VOQxfB3bon8tNTAbaoyQOjbkkFr9E7c5BXZrhpSY87szyM6HhPhLdhveialXUBU DqzRCadpsUll9LREIS1K/RXRPcaIokvVnVnPDzXmSVZJ2/ObX6ocR1K2ZGP/5TkdOHxCq1 ELIYL97JJZy+oNEpgveNV8ZUXppn1Vk= Date: Thu, 5 Sep 2024 20:07:00 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v3 10/14] mm: page_vma_mapped_walk: map_pte() use pte_offset_map_rw_nolock() To: Qi Zheng Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, david@redhat.com, hughd@google.com, willy@infradead.org, vbabka@kernel.org, akpm@linux-foundation.org, rppt@kernel.org, vishal.moola@gmail.com, peterx@redhat.com, ryan.roberts@arm.com, christophe.leroy2@cs-soprasteria.com References: <20240904084022.32728-1-zhengqi.arch@bytedance.com> <20240904084022.32728-11-zhengqi.arch@bytedance.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Muchun Song In-Reply-To: <20240904084022.32728-11-zhengqi.arch@bytedance.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 2024/9/4 16:40, Qi Zheng wrote: > In the caller of map_pte(), we may modify the pvmw->pte after acquiring > the pvmw->ptl, so convert it to using pte_offset_map_rw_nolock(). At > this time, the pte_same() check is not performed after the pvmw->ptl held, > so we should get pmdval and do pmd_same() check to ensure the stability of > pvmw->pmd. > > Signed-off-by: Qi Zheng > --- > mm/page_vma_mapped.c | 24 ++++++++++++++++++++---- > 1 file changed, 20 insertions(+), 4 deletions(-) > > diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c > index ae5cc42aa2087..f1d73fd448708 100644 > --- a/mm/page_vma_mapped.c > +++ b/mm/page_vma_mapped.c > @@ -13,9 +13,11 @@ static inline bool not_found(struct page_vma_mapped_walk *pvmw) > return false; > } > > -static bool map_pte(struct page_vma_mapped_walk *pvmw, spinlock_t **ptlp) > +static bool map_pte(struct page_vma_mapped_walk *pvmw, pmd_t *pmdvalp, > + spinlock_t **ptlp) > { > pte_t ptent; > + pmd_t pmdval; > > if (pvmw->flags & PVMW_SYNC) { > /* Use the stricter lookup */ > @@ -25,6 +27,7 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw, spinlock_t **ptlp) > return !!pvmw->pte; > } > > +again: > /* > * It is important to return the ptl corresponding to pte, > * in case *pvmw->pmd changes underneath us; so we need to > @@ -32,10 +35,11 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw, spinlock_t **ptlp) > * proceeds to loop over next ptes, and finds a match later. > * Though, in most cases, page lock already protects this. > */ > - pvmw->pte = pte_offset_map_nolock(pvmw->vma->vm_mm, pvmw->pmd, > - pvmw->address, ptlp); > + pvmw->pte = pte_offset_map_rw_nolock(pvmw->vma->vm_mm, pvmw->pmd, > + pvmw->address, &pmdval, ptlp); > if (!pvmw->pte) > return false; > + *pmdvalp = pmdval; > > ptent = ptep_get(pvmw->pte); > > @@ -69,6 +73,12 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw, spinlock_t **ptlp) > } > pvmw->ptl = *ptlp; > spin_lock(pvmw->ptl); > + > + if (unlikely(!pmd_same(pmdval, pmdp_get_lockless(pvmw->pmd)))) { > + spin_unlock(pvmw->ptl); Forgot to clear pvmw->ptl? Or how about moving the assignment for it to the place where the pmd_same check is successful? > + goto again; > + } > + Maybe here is the right place to assign pvmw->ptl. Muchun, Thanks. > return true; > } > > @@ -278,7 +288,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) > step_forward(pvmw, PMD_SIZE); > continue; > } > - if (!map_pte(pvmw, &ptl)) { > + if (!map_pte(pvmw, &pmde, &ptl)) { > if (!pvmw->pte) > goto restart; > goto next_pte; > @@ -307,6 +317,12 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) > if (!pvmw->ptl) { > pvmw->ptl = ptl; > spin_lock(pvmw->ptl); > + if (unlikely(!pmd_same(pmde, pmdp_get_lockless(pvmw->pmd)))) { > + pte_unmap_unlock(pvmw->pte, pvmw->ptl); > + pvmw->ptl = NULL; > + pvmw->pte = NULL; > + goto restart; > + } > } > goto this_pte; > } while (pvmw->address < end);