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Sun, 25 Apr 2021 23:53:46 -0700 (PDT) MIME-Version: 1.0 References: <20210425095419.3830298-1-linmiaohe@huawei.com> <20210425095419.3830298-5-linmiaohe@huawei.com> In-Reply-To: <20210425095419.3830298-5-linmiaohe@huawei.com> From: Yu Zhao Date: Mon, 26 Apr 2021 00:53:34 -0600 Message-ID: Subject: Re: [PATCH v5 4/4] mm/shmem: fix shmem_swapin() race with swapoff To: Miaohe Lin Cc: Andrew Morton , Huang Ying , dennis@kernel.org, Tim Chen , Hugh Dickins , Johannes Weiner , Michal Hocko , Joonsoo Kim , alexs@kernel.org, Matthew Wilcox , Minchan Kim , Wei Yang , Yang Shi , David Hildenbrand , linux-kernel , Linux-MM Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: DE34EE00010B X-Stat-Signature: 5hk165hx4s718sminoefbyru5se6qobf Received-SPF: none (google.com>: No applicable sender policy available) receiver=imf13; identity=mailfrom; envelope-from=""; helo=mail-wm1-f41.google.com; client-ip=209.85.128.41 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1619420020-104753 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sun, Apr 25, 2021 at 3:54 AM Miaohe Lin wrote: > > When I was investigating the swap code, I found the below possible race > window: > > CPU 1 CPU 2 > ----- ----- > shmem_swapin > swap_cluster_readahead > if (likely(si->flags & (SWP_BLKDEV | SWP_FS_OPS))) { > swapoff > .. > si->swap_file = NULL; > .. > struct inode *inode = si->swap_file->f_mapping->host;[oops!] > > Close this race window by using get/put_swap_device() to guard against > concurrent swapoff. > > Fixes: 8fd2e0b505d1 ("mm: swap: check if swap backing device is congested or not") > Signed-off-by: Miaohe Lin > --- > mm/shmem.c | 12 ++++++++++++ > 1 file changed, 12 insertions(+) > > diff --git a/mm/shmem.c b/mm/shmem.c > index 26c76b13ad23..2dafd65b0b42 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -1696,6 +1696,7 @@ static int shmem_swapin_page(struct inode *inode, pgoff_t index, > struct address_space *mapping = inode->i_mapping; > struct shmem_inode_info *info = SHMEM_I(inode); > struct mm_struct *charge_mm = vma ? vma->vm_mm : current->mm; > + struct swap_info_struct *si; > struct page *page; > swp_entry_t swap; > int error; > @@ -1704,6 +1705,12 @@ static int shmem_swapin_page(struct inode *inode, pgoff_t index, > swap = radix_to_swp_entry(*pagep); > *pagep = NULL; > > + /* Prevent swapoff from happening to us. */ > + si = get_swap_device(swap); > + if (!si) { > + error = EINVAL; > + goto failed; > + } page is uninitialized? > /* Look it up and read it in.. */ > page = lookup_swap_cache(swap, NULL, 0); > if (!page) { > @@ -1765,6 +1772,8 @@ static int shmem_swapin_page(struct inode *inode, pgoff_t index, > swap_free(swap); > > *pagep = page; > + if (si) > + put_swap_device(si); > return 0; > failed: > if (!shmem_confirm_swap(mapping, index, swap)) > @@ -1775,6 +1784,9 @@ static int shmem_swapin_page(struct inode *inode, pgoff_t index, > put_page(page); > } > > + if (si) > + put_swap_device(si); > + > return error; > } > > -- > 2.23.0 > >