From patchwork Mon Jul 13 17:28:15 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Chris Down X-Patchwork-Id: 11660809 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 5791A13B4 for ; Mon, 13 Jul 2020 17:28:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3D1502076D for ; Mon, 13 Jul 2020 17:28:22 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chrisdown.name header.i=@chrisdown.name header.b="uzOJKoX8" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730421AbgGMR2V (ORCPT ); Mon, 13 Jul 2020 13:28:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57366 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730380AbgGMR2R (ORCPT ); Mon, 13 Jul 2020 13:28:17 -0400 Received: from mail-ej1-x641.google.com (mail-ej1-x641.google.com [IPv6:2a00:1450:4864:20::641]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4888DC061794 for ; Mon, 13 Jul 2020 10:28:17 -0700 (PDT) Received: by mail-ej1-x641.google.com with SMTP id f12so18156107eja.9 for ; Mon, 13 Jul 2020 10:28:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chrisdown.name; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=lAw1dZEFjnFeT9loip9ug9GZCnCHV+9F05rbN8HJwXo=; b=uzOJKoX8CZ3z6Ueq9TF/Kov5JEogHxmvVnhsDfSkDnY4U+PTy8BJylYKqRBVw7ZF8X jT3vuFKia7DopfuXtC9AxtTJAWIUOrAohBVGmYMVX2ZNc/RlE1dyPjz0XykLQI72Jprf PV4cmdd2cJWVhj+eWiic0jXLj33/QE+QGLMy8= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=lAw1dZEFjnFeT9loip9ug9GZCnCHV+9F05rbN8HJwXo=; b=QRVdOPECXZfWQDze4zKqgRYlAYTR78l2Goxk2kgC8wEt74TAYw76012NMTlt11rmHS JEbTxH7pJiA6aV0b5qnrW2nsGZahttybWT7KC1jVLfe3ew0ocsuZ8+yY7UyxO3E31a9t MqDmc+CekmMbQYR40Mgqv6+RtlCw3JBw/mzQiGbPj3YETYKIkpvnHQKfzKW0OhuJO9vs sfMmW5FaF0qWVqN+/TUezU8oW9j9Xf7ieBsirUzyzE7SFjkssf+g49b5psDfMcAuOjBc g1G9AXs+LzM25nF3+fp+rB1TeNR6M8Pb9O2nQu+iBcdtNMzPUHLrUmHpsqN6yXSXYIdZ i2bg== X-Gm-Message-State: AOAM532UaAODtYP2H9oxiotTytYLOS8WjY4Nq4OlTq4nMM3DzN+l38wk x9Fg2U9Q7TXCwG3RksGXijl60w== X-Google-Smtp-Source: ABdhPJyFfdljDqwF/Jf9HT1imvTpTzxHomhkSeYf3CTCe74uewyvJiqsXwkbIn1F12F+2DUPKbecpQ== X-Received: by 2002:a17:906:8542:: with SMTP id h2mr703721ejy.517.1594661295897; Mon, 13 Jul 2020 10:28:15 -0700 (PDT) Received: from localhost ([2620:10d:c093:400::5:ef88]) by smtp.gmail.com with ESMTPSA id w8sm10329473ejb.10.2020.07.13.10.28.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 13 Jul 2020 10:28:15 -0700 (PDT) Date: Mon, 13 Jul 2020 18:28:15 +0100 From: Chris Down To: Andrew Morton Cc: Hugh Dickins , Al Viro , Matthew Wilcox , Amir Goldstein , Jeff Layton , Johannes Weiner , Tejun Heo , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: [PATCH v7 1/2] tmpfs: Per-superblock i_ino support Message-ID: <1986b9d63b986f08ec07a4aa4b2275e718e47d8a.1594661218.git.chris@chrisdown.name> References: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.14.5 (2020-06-23) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org get_next_ino has a number of problems: - It uses and returns a uint, which is susceptible to become overflowed if a lot of volatile inodes that use get_next_ino are created. - It's global, with no specificity per-sb or even per-filesystem. This means it's not that difficult to cause inode number wraparounds on a single device, which can result in having multiple distinct inodes with the same inode number. This patch adds a per-superblock counter that mitigates the second case. This design also allows us to later have a specific i_ino size per-device, for example, allowing users to choose whether to use 32- or 64-bit inodes for each tmpfs mount. This is implemented in the next commit. For internal shmem mounts which may be less tolerant to spinlock delays, we implement a percpu batching scheme which only takes the stat_lock at each batch boundary. Signed-off-by: Chris Down Cc: Amir Goldstein Cc: Hugh Dickins Cc: Andrew Morton Cc: Al Viro Cc: Matthew Wilcox Cc: Jeff Layton Cc: Johannes Weiner Cc: Tejun Heo Cc: linux-mm@kvack.org Cc: linux-fsdevel@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: kernel-team@fb.com Acked-by: Hugh Dickins --- include/linux/fs.h | 15 +++++++++ include/linux/shmem_fs.h | 2 ++ mm/shmem.c | 66 +++++++++++++++++++++++++++++++++++++--- 3 files changed, 78 insertions(+), 5 deletions(-) diff --git a/include/linux/fs.h b/include/linux/fs.h index f15848899945..b70b334f8e16 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -2961,6 +2961,21 @@ extern void discard_new_inode(struct inode *); extern unsigned int get_next_ino(void); extern void evict_inodes(struct super_block *sb); +/* + * Userspace may rely on the the inode number being non-zero. For example, glibc + * simply ignores files with zero i_ino in unlink() and other places. + * + * As an additional complication, if userspace was compiled with + * _FILE_OFFSET_BITS=32 on a 64-bit kernel we'll only end up reading out the + * lower 32 bits, so we need to check that those aren't zero explicitly. With + * _FILE_OFFSET_BITS=64, this may cause some harmless false-negatives, but + * better safe than sorry. + */ +static inline bool is_zero_ino(ino_t ino) +{ + return (u32)ino == 0; +} + extern void __iget(struct inode * inode); extern void iget_failed(struct inode *); extern void clear_inode(struct inode *); diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h index 7a35a6901221..eb628696ec66 100644 --- a/include/linux/shmem_fs.h +++ b/include/linux/shmem_fs.h @@ -36,6 +36,8 @@ struct shmem_sb_info { unsigned char huge; /* Whether to try for hugepages */ kuid_t uid; /* Mount uid for root directory */ kgid_t gid; /* Mount gid for root directory */ + ino_t next_ino; /* The next per-sb inode number to use */ + ino_t __percpu *ino_batch; /* The next per-cpu inode number to use */ struct mempolicy *mpol; /* default memory policy for mappings */ spinlock_t shrinklist_lock; /* Protects shrinklist */ struct list_head shrinklist; /* List of shinkable inodes */ diff --git a/mm/shmem.c b/mm/shmem.c index a0dbe62f8042..0ae250b4da28 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -260,18 +260,67 @@ bool vma_is_shmem(struct vm_area_struct *vma) static LIST_HEAD(shmem_swaplist); static DEFINE_MUTEX(shmem_swaplist_mutex); -static int shmem_reserve_inode(struct super_block *sb) +/* + * shmem_reserve_inode() performs bookkeeping to reserve a shmem inode, and + * produces a novel ino for the newly allocated inode. + * + * It may also be called when making a hard link to permit the space needed by + * each dentry. However, in that case, no new inode number is needed since that + * internally draws from another pool of inode numbers (currently global + * get_next_ino()). This case is indicated by passing NULL as inop. + */ +#define SHMEM_INO_BATCH 1024 +static int shmem_reserve_inode(struct super_block *sb, ino_t *inop) { struct shmem_sb_info *sbinfo = SHMEM_SB(sb); - if (sbinfo->max_inodes) { + ino_t ino; + + if (!(sb->s_flags & SB_KERNMOUNT)) { spin_lock(&sbinfo->stat_lock); if (!sbinfo->free_inodes) { spin_unlock(&sbinfo->stat_lock); return -ENOSPC; } sbinfo->free_inodes--; + if (inop) { + ino = sbinfo->next_ino++; + if (unlikely(is_zero_ino(ino))) + ino = sbinfo->next_ino++; + if (unlikely(ino > UINT_MAX)) { + /* + * Emulate get_next_ino uint wraparound for + * compatibility + */ + ino = 1; + } + *inop = ino; + } spin_unlock(&sbinfo->stat_lock); + } else if (inop) { + /* + * __shmem_file_setup, one of our callers, is lock-free: it + * doesn't hold stat_lock in shmem_reserve_inode since + * max_inodes is always 0, and is called from potentially + * unknown contexts. As such, use a per-cpu batched allocator + * which doesn't require the per-sb stat_lock unless we are at + * the batch boundary. + */ + ino_t *next_ino; + next_ino = per_cpu_ptr(sbinfo->ino_batch, get_cpu()); + ino = *next_ino; + if (unlikely(ino % SHMEM_INO_BATCH == 0)) { + spin_lock(&sbinfo->stat_lock); + ino = sbinfo->next_ino; + sbinfo->next_ino += SHMEM_INO_BATCH; + spin_unlock(&sbinfo->stat_lock); + if (unlikely(is_zero_ino(ino))) + ino++; + } + *inop = ino; + *next_ino = ++ino; + put_cpu(); } + return 0; } @@ -2222,13 +2271,14 @@ static struct inode *shmem_get_inode(struct super_block *sb, const struct inode struct inode *inode; struct shmem_inode_info *info; struct shmem_sb_info *sbinfo = SHMEM_SB(sb); + ino_t ino; - if (shmem_reserve_inode(sb)) + if (shmem_reserve_inode(sb, &ino)) return NULL; inode = new_inode(sb); if (inode) { - inode->i_ino = get_next_ino(); + inode->i_ino = ino; inode_init_owner(inode, dir, mode); inode->i_blocks = 0; inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode); @@ -2932,7 +2982,7 @@ static int shmem_link(struct dentry *old_dentry, struct inode *dir, struct dentr * first link must skip that, to get the accounting right. */ if (inode->i_nlink) { - ret = shmem_reserve_inode(inode->i_sb); + ret = shmem_reserve_inode(inode->i_sb, NULL); if (ret) goto out; } @@ -3584,6 +3634,7 @@ static void shmem_put_super(struct super_block *sb) { struct shmem_sb_info *sbinfo = SHMEM_SB(sb); + free_percpu(sbinfo->ino_batch); percpu_counter_destroy(&sbinfo->used_blocks); mpol_put(sbinfo->mpol); kfree(sbinfo); @@ -3626,6 +3677,11 @@ static int shmem_fill_super(struct super_block *sb, struct fs_context *fc) #endif sbinfo->max_blocks = ctx->blocks; sbinfo->free_inodes = sbinfo->max_inodes = ctx->inodes; + if (sb->s_flags & SB_KERNMOUNT) { + sbinfo->ino_batch = alloc_percpu(ino_t); + if (!sbinfo->ino_batch) + goto failed; + } sbinfo->uid = ctx->uid; sbinfo->gid = ctx->gid; sbinfo->mode = ctx->mode;