From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-170.mta1.migadu.com (out-170.mta1.migadu.com [95.215.58.170]) (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 624803085D7 for ; Thu, 19 Jun 2025 08:29:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.170 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750321757; cv=none; b=ArIUuIaaMgEnWUP23GizROr31mCbmeot0yWFlLu2+z0qbHeINE9VaaTQ59uFBtWv/s4FVQd03auDz1n6mSLL2GVrHDt/kMsYl3Mk8jASch0HRBsOfusbMtCu0hVoWWJo7YnoxDlbOF0XF3510/bs1quvJAfdFghlPgBriRmOOD4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750321757; c=relaxed/simple; bh=8kp8MhtBooyZ24xJw3HE3NBv31unIexU5R/0rv70u4M=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=sCUkj44zh+S+ARxtIveBShWXjfwtBzwslqJUnJauJx3QYYIQ44CbZJNWI1XH+ybMGabHiEElhOpQyO1FgpyYNOfcjjmnR9mjPbCnt6b/AtKdZHf5HNGCpmlASWrmv+Z7QIryomZzI/2obyPx08wXZW8CI3roIkRDPHQcNqCEjfQ= 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=K3VXHu30; arc=none smtp.client-ip=95.215.58.170 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="K3VXHu30" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1750321752; 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=LwqkJWv+ifVhzjp8MQr7Ddsa5ddsAXMB/QGydZH0ApY=; b=K3VXHu30ZHT9FCDaKQNMGBS0HsUIyVXQ3ojsfC/llhBDDhO5YmRJilmvtbxDn7tI2YHgza 7NXVqzwdr5RZ5caKtFhe6dTZ131c57faBudgVlm5QaZXU1O7fDuW7zDudr70AQbr0i3P4+ GgwbfK/SEsof8nJbFMT2aExpuKLKjVI= Date: Thu, 19 Jun 2025 16:28:53 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH] mm/rmap: Add NULL checks for rmap_walk_control callbacks To: Dev Jain , Andrew Morton , David Hildenbrand , Lorenzo Stoakes Cc: Ye Liu , Xu Xin , Chengming Zhou , Rik van Riel , "Liam R. Howlett" , Vlastimil Babka , Harry Yoo , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20250619075040.796047-1-ye.liu@linux.dev> <9454603f-c187-4386-8244-69f304197954@arm.com> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Ye Liu In-Reply-To: <9454603f-c187-4386-8244-69f304197954@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT Hi Lorenzo and Dev, Thanks for your feedback. I understand all your points and will drop this patch. Best regards, Ye Liu On 2025/6/19 16:17, Dev Jain wrote: > > On 19/06/25 1:20 pm, Ye Liu wrote: >> From: Ye Liu >> >> Add NULL pointer checks for rmap_one callback in rmap_walk operations >> to prevent potential NULL pointer dereferences. Also clean up some >> code by removing redundant comments and caching folio_nr_pages(). >> >> Signed-off-by: Ye Liu >> --- > > Don't really see the point of this patch. The rmap_one call back will > always be there as we need a way to define how to unmap/do the reverse > map walk for one VMA at a time. And the folio_nr_pages() will probably > get cached by the compiler anyways. > >>   mm/ksm.c  |  2 +- >>   mm/rmap.c | 14 +++++++------- >>   2 files changed, 8 insertions(+), 8 deletions(-) >> >> diff --git a/mm/ksm.c b/mm/ksm.c >> index 18b3690bb69a..22ad069d1860 100644 >> --- a/mm/ksm.c >> +++ b/mm/ksm.c >> @@ -3068,7 +3068,7 @@ void rmap_walk_ksm(struct folio *folio, struct rmap_walk_control *rwc) >>               if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg)) >>                   continue; >>   -            if (!rwc->rmap_one(folio, vma, addr, rwc->arg)) { >> +            if (rwc->rmap_one && !rwc->rmap_one(folio, vma, addr, rwc->arg)) { >>                   anon_vma_unlock_read(anon_vma); >>                   return; >>               } >> diff --git a/mm/rmap.c b/mm/rmap.c >> index fb63d9256f09..17d43d104a0d 100644 >> --- a/mm/rmap.c >> +++ b/mm/rmap.c >> @@ -1202,8 +1202,7 @@ int mapping_wrprotect_range(struct address_space *mapping, pgoff_t pgoff, >>       if (!mapping) >>           return 0; >>   -    __rmap_walk_file(/* folio = */NULL, mapping, pgoff, nr_pages, &rwc, >> -             /* locked = */false); >> +    __rmap_walk_file(NULL, mapping, pgoff, nr_pages, &rwc, false); >>         return state.cleaned; >>   } >> @@ -2806,6 +2805,7 @@ static void rmap_walk_anon(struct folio *folio, >>       struct anon_vma *anon_vma; >>       pgoff_t pgoff_start, pgoff_end; >>       struct anon_vma_chain *avc; >> +    unsigned long nr_pages; >>         if (locked) { >>           anon_vma = folio_anon_vma(folio); >> @@ -2817,13 +2817,13 @@ static void rmap_walk_anon(struct folio *folio, >>       if (!anon_vma) >>           return; >>   +    nr_pages = folio_nr_pages(folio); >>       pgoff_start = folio_pgoff(folio); >> -    pgoff_end = pgoff_start + folio_nr_pages(folio) - 1; >> +    pgoff_end = pgoff_start + nr_pages - 1; >>       anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, >>               pgoff_start, pgoff_end) { >>           struct vm_area_struct *vma = avc->vma; >> -        unsigned long address = vma_address(vma, pgoff_start, >> -                folio_nr_pages(folio)); >> +        unsigned long address = vma_address(vma, pgoff_start, nr_pages); >>             VM_BUG_ON_VMA(address == -EFAULT, vma); >>           cond_resched(); >> @@ -2831,7 +2831,7 @@ static void rmap_walk_anon(struct folio *folio, >>           if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg)) >>               continue; >>   -        if (!rwc->rmap_one(folio, vma, address, rwc->arg)) >> +        if (rwc->rmap_one && !rwc->rmap_one(folio, vma, address, rwc->arg)) >>               break; >>           if (rwc->done && rwc->done(folio)) >>               break; >> @@ -2894,7 +2894,7 @@ static void __rmap_walk_file(struct folio *folio, struct address_space *mapping, >>           if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg)) >>               continue; >>   -        if (!rwc->rmap_one(folio, vma, address, rwc->arg)) >> +        if (rwc->rmap_one && !rwc->rmap_one(folio, vma, address, rwc->arg)) >>               goto done; >>           if (rwc->done && rwc->done(folio)) >>               goto done;