From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-119.freemail.mail.aliyun.com (out30-119.freemail.mail.aliyun.com [115.124.30.119]) (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 BAE371B4140 for ; Thu, 15 May 2025 03:59:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.119 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747281568; cv=none; b=mI61qU1Gju1G6pOP6moYngzONdqcEyymdAfiz8LJdopYn9nQ5If1DNny8fgag10oBokzotrYXJP8SJMX2fmMgCAF2Vz4lzv/hhoiUpcAfJ45ea/8h5Ttq2WfVhCjr2NzD5mZZxf8G3fTZn0BJkNsQmd9q0jp7Gurzw+cYdiOILA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747281568; c=relaxed/simple; bh=whQizIeyGW42Zl99GNuqjMQ5PXU6M7matiCigSNfyM8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=k363oOeEB9jkXsQr3MOgpleJ09XkpT4ZRXT8biq/9YDAW4APxXiFwlVA9gtMpfhRd+zJO4GBplYa5TEYSppjdd3G01j0PwA8MaAbkOIGxz0Xv8Pc1c00Xecf1wZjHKCui3seDvCosB6q3uzbikZHV2fdUnYT4YcnN1L09SSYZ04= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=QOG3g1we; arc=none smtp.client-ip=115.124.30.119 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="QOG3g1we" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1747281555; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=TFdZ6vQjYgvoP+lEGuUuMLwUa7mcXBQhvQk2iDXRQ5U=; b=QOG3g1weY7bke/tLe/B0mRJzxes4mNcV2bReeK1JzSdFTDM6GoSe6J56FreedYw4oqnYA/sblvMxyMevOCsuxKvubsnrkrstKkmHufSOTQ4nN5eJPfaiIBjBgBzTOXWHI+q+RiQH25AVSfpm1viWVzEij1LpfxkdKz5ciO7VqwY= Received: from 30.74.144.114(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0Wap9KyY_1747281555 cluster:ay36) by smtp.aliyun-inc.com; Thu, 15 May 2025 11:59:15 +0800 Message-ID: <453015aa-e18f-4e37-86b1-001ec4e994d1@linux.alibaba.com> Date: Thu, 15 May 2025 11:59:13 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/5] mm/shmem: Fix potential dead loop in shmem_unuse() To: Kemeng Shi , hughd@google.com, akpm@linux-foundation.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20250514165047.946884-1-shikemeng@huaweicloud.com> <20250514165047.946884-4-shikemeng@huaweicloud.com> <634a73ce-a24e-01d4-1d00-86272bc78860@huaweicloud.com> From: Baolin Wang In-Reply-To: <634a73ce-a24e-01d4-1d00-86272bc78860@huaweicloud.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2025/5/15 09:05, Kemeng Shi wrote: > > > on 5/14/2025 5:24 PM, Baolin Wang wrote: >> >> >> On 2025/5/15 00:50, Kemeng Shi wrote: >>> If multi shmem_unuse() for different swap type is called concurrently, >>> a dead loop could occur as following: >>> shmem_unuse(typeA)               shmem_unuse(typeB) >>>   mutex_lock(&shmem_swaplist_mutex) >>>   list_for_each_entry_safe(info, next, ...) >>>    ... >>>    mutex_unlock(&shmem_swaplist_mutex) >>>    /* info->swapped may drop to 0 */ >>>    shmem_unuse_inode(&info->vfs_inode, type) >>> >>>                                    mutex_lock(&shmem_swaplist_mutex) >>>                                    list_for_each_entry(info, next, ...) >>>                                     if (!info->swapped) >>>                                      list_del_init(&info->swaplist) >>> >>>                                    ... >>>                                    mutex_unlock(&shmem_swaplist_mutex) >>> >>>    mutex_lock(&shmem_swaplist_mutex) >>>    /* iterate with offlist entry and encounter a dead loop */ >>>    next = list_next_entry(info, swaplist); >>>    ... >>> >>> Restart the iteration if the inode is already off shmem_swaplist list >>> to fix the issue. >>> >>> Fixes: b56a2d8af9147 ("mm: rid swapoff of quadratic complexity") >>> Signed-off-by: Kemeng Shi >>> --- >>>   mm/shmem.c | 3 +++ >>>   1 file changed, 3 insertions(+) >>> >>> diff --git a/mm/shmem.c b/mm/shmem.c >>> index 495e661eb8bb..0fed94c2bc09 100644 >>> --- a/mm/shmem.c >>> +++ b/mm/shmem.c >>> @@ -1505,6 +1505,7 @@ int shmem_unuse(unsigned int type) >>>           return 0; >>>         mutex_lock(&shmem_swaplist_mutex); >>> +start_over: >>>       list_for_each_entry_safe(info, next, &shmem_swaplist, swaplist) { >>>           if (!info->swapped) { >>>               list_del_init(&info->swaplist); >>> @@ -1530,6 +1531,8 @@ int shmem_unuse(unsigned int type) >> >>         next = list_next_entry(info, swaplist); >>         if (!info->swapped) >>             list_del_init(&info->swaplist); >>         if (atomic_dec_and_test(&info->stop_eviction)) >>             wake_up_var(&info->stop_eviction); >> >> We may still hit the list warning when calling list_del_init() for the off-list info->swaplist? So I hope we can add a check for the possible off-list: > Hello, > When entry is taken off list, it will be initialized to a valid empty entry > with INIT_LIST_HEAD(). So it should be fine to call list_del_init() for > off-list entry. > Please correct me if I miss anything. Thanks! Ah, yes. I got confused with list_del(), but I still think we should not continue to operate on an off-list entry. >> diff --git a/mm/shmem.c b/mm/shmem.c >> index 99327c30507c..f5ae5e2d6fb4 100644 >> --- a/mm/shmem.c >> +++ b/mm/shmem.c >> @@ -1523,9 +1523,11 @@ int shmem_unuse(unsigned int type) >>                 cond_resched(); >> >>                 mutex_lock(&shmem_swaplist_mutex); >> -               next = list_next_entry(info, swaplist); >> -               if (!info->swapped) >> -                       list_del_init(&info->swaplist); >> +               if (!list_empty(&info->swaplist)) { >> +                       next = list_next_entry(info, swaplist); >> +                       if (!info->swapped) >> +                               list_del_init(&info->swaplist); >> +               } >>                 if (atomic_dec_and_test(&info->stop_eviction)) >>                         wake_up_var(&info->stop_eviction); >>                 if (error) >> >>>               wake_up_var(&info->stop_eviction); >>>           if (error) >>>               break; >>> +        if (list_empty(&info->swaplist)) >>> +            goto start_over; >>>       } >>>       mutex_unlock(&shmem_swaplist_mutex); >>> >>