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Wed, 28 Jan 2026 01:30:35 -0800 (PST) Received: from [127.0.0.1] ([43.132.141.21]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3540f3eca6dsm1872235a91.15.2026.01.28.01.30.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 28 Jan 2026 01:30:34 -0800 (PST) From: Kairui Song Date: Wed, 28 Jan 2026 17:28:25 +0800 Subject: [PATCH v2 01/12] mm, swap: protect si->swap_file properly and use as a mount indicator MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260128-swap-table-p3-v2-1-fe0b67ef0215@tencent.com> References: <20260128-swap-table-p3-v2-0-fe0b67ef0215@tencent.com> In-Reply-To: <20260128-swap-table-p3-v2-0-fe0b67ef0215@tencent.com> To: linux-mm@kvack.org Cc: Andrew Morton , Kemeng Shi , Nhat Pham , Baoquan He , Barry Song , Johannes Weiner , David Hildenbrand , Lorenzo Stoakes , Youngjun Park , linux-kernel@vger.kernel.org, Chris Li , Kairui Song X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=ed25519-sha256; t=1769592628; l=5423; i=kasong@tencent.com; s=kasong-sign-tencent; h=from:subject:message-id; bh=KCJ3euqA2qAaRKKZ+5BOjIB6OnqWy66OxHgNUHCngaI=; b=yUDffmpYnq0E0QTlzeFqQIlUHmu6snQJuTNpipCSscvVCs/a0w84zEQXy7hojSBMeXeMrbeiT uuD5ZksxBlFCx3xtlmgpeUcAp/e/Q7vCV0UdfEg0XIrukAPUSaAbqkI X-Developer-Key: i=kasong@tencent.com; a=ed25519; pk=kCdoBuwrYph+KrkJnrr7Sm1pwwhGDdZKcKrqiK8Y1mI= X-Rspamd-Queue-Id: 83C7D80011 X-Stat-Signature: 58sijs1x9xnhu5ag74uidtfyknnq6xec X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1769592636-676359 X-HE-Meta: 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 Hc+RnIQi +q4lJbB5xOfcDNL/0OCr5RNzJ88GRSCwzS6dUcgv+d7pIbsLDVJn2NPmrXVnVp/ls8dCnKChVynuujw7P9meJyv/ZzzGa7vsg6KBk8Lu4CIsMEfCeULgdeAUVKK9mDPrHhxy43UYtuNmqzyqlE11875U7eHS/HPtV7iZhwIHdxLJ8+kh6IJ4AQ0QRB2MR060fiFFOCTL4jQk9Pe8abu+T3tpAzbcDnFSVZH7OaSAgeS1tlPEuT8P93ZLi/bbs1CvQQO96Odnr7rGa98+3TIcdxiC0ctH909E6s68qq+DJhuPenu+pODhGqzH8bG776K7iWOm+lXvvvf1hja7zXzp5qXOb/Y9L98SRXquYLjJBOtOUH/Qn0v9YFpzkKwU8TVa+1ucdATnZau9JWaCnXkoDWBgIlsYK6BboMijrz/VhvzqkdfqGapAlbupLHcj1vmxYJXcByIBqbvYKvHSMu0Uc5tQumq0IhmplPDN7 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: List-Subscribe: List-Unsubscribe: From: Kairui Song /proc/swaps uses si->swap_map as the indicator to check if the swap device is mounted. swap_map will be removed soon, so change it to use si->swap_file instead because: - si->swap_file is exactly the only dynamic content that /proc/swaps is interested in. Previously, it was checking si->swap_map just to ensure si->swap_file is available. si->swap_map is set under mutex protection, and after si->swap_file is set, so having si->swap_map set guarantees si->swap_file is set. - Checking si->flags doesn't work here. SWP_WRITEOK is cleared during swapoff, but /proc/swaps is supposed to show the device under swapoff too to report the swapoff progress. And SWP_USED is set even if the device hasn't been properly set up. We can have another flag, but the easier way is to just check si->swap_file directly. So protect si->swap_file setting with mutext, and set si->swap_file only when the swap device is truly enabled. /proc/swaps only interested in si->swap_file and a few static data reading. Only si->swap_file needs protection. Reading other static fields is always fine. Signed-off-by: Kairui Song --- mm/swapfile.c | 25 +++++++++++++------------ 1 file changed, 13 insertions(+), 12 deletions(-) diff --git a/mm/swapfile.c b/mm/swapfile.c index 7b055f15d705..521f7713a7c3 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -110,6 +110,7 @@ struct swap_info_struct *swap_info[MAX_SWAPFILES]; static struct kmem_cache *swap_table_cachep; +/* Protects si->swap_file for /proc/swaps usage */ static DEFINE_MUTEX(swapon_mutex); static DECLARE_WAIT_QUEUE_HEAD(proc_poll_wait); @@ -2521,7 +2522,8 @@ static void drain_mmlist(void) /* * Free all of a swapdev's extent information */ -static void destroy_swap_extents(struct swap_info_struct *sis) +static void destroy_swap_extents(struct swap_info_struct *sis, + struct file *swap_file) { while (!RB_EMPTY_ROOT(&sis->swap_extent_root)) { struct rb_node *rb = sis->swap_extent_root.rb_node; @@ -2532,7 +2534,6 @@ static void destroy_swap_extents(struct swap_info_struct *sis) } if (sis->flags & SWP_ACTIVATED) { - struct file *swap_file = sis->swap_file; struct address_space *mapping = swap_file->f_mapping; sis->flags &= ~SWP_ACTIVATED; @@ -2615,9 +2616,9 @@ EXPORT_SYMBOL_GPL(add_swap_extent); * Typically it is in the 1-4 megabyte range. So we can have hundreds of * extents in the rbtree. - akpm. */ -static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span) +static int setup_swap_extents(struct swap_info_struct *sis, + struct file *swap_file, sector_t *span) { - struct file *swap_file = sis->swap_file; struct address_space *mapping = swap_file->f_mapping; struct inode *inode = mapping->host; int ret; @@ -2635,7 +2636,7 @@ static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span) sis->flags |= SWP_ACTIVATED; if ((sis->flags & SWP_FS_OPS) && sio_pool_init() != 0) { - destroy_swap_extents(sis); + destroy_swap_extents(sis, swap_file); return -ENOMEM; } return ret; @@ -2851,7 +2852,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) flush_work(&p->reclaim_work); flush_percpu_swap_cluster(p); - destroy_swap_extents(p); + destroy_swap_extents(p, p->swap_file); if (p->flags & SWP_CONTINUED) free_swap_count_continuations(p); @@ -2941,7 +2942,7 @@ static void *swap_start(struct seq_file *swap, loff_t *pos) return SEQ_START_TOKEN; for (type = 0; (si = swap_type_to_info(type)); type++) { - if (!(si->flags & SWP_USED) || !si->swap_map) + if (!(si->swap_file)) continue; if (!--l) return si; @@ -2962,7 +2963,7 @@ static void *swap_next(struct seq_file *swap, void *v, loff_t *pos) ++(*pos); for (; (si = swap_type_to_info(type)); type++) { - if (!(si->flags & SWP_USED) || !si->swap_map) + if (!(si->swap_file)) continue; return si; } @@ -3379,7 +3380,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) goto bad_swap; } - si->swap_file = swap_file; mapping = swap_file->f_mapping; dentry = swap_file->f_path.dentry; inode = mapping->host; @@ -3429,7 +3429,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) si->max = maxpages; si->pages = maxpages - 1; - nr_extents = setup_swap_extents(si, &span); + nr_extents = setup_swap_extents(si, swap_file, &span); if (nr_extents < 0) { error = nr_extents; goto bad_swap_unlock_inode; @@ -3538,6 +3538,8 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) prio = DEF_SWAP_PRIO; if (swap_flags & SWAP_FLAG_PREFER) prio = swap_flags & SWAP_FLAG_PRIO_MASK; + + si->swap_file = swap_file; enable_swap_info(si, prio, swap_map, cluster_info, zeromap); pr_info("Adding %uk swap on %s. Priority:%d extents:%d across:%lluk %s%s%s%s\n", @@ -3562,10 +3564,9 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) kfree(si->global_cluster); si->global_cluster = NULL; inode = NULL; - destroy_swap_extents(si); + destroy_swap_extents(si, swap_file); swap_cgroup_swapoff(si->type); spin_lock(&swap_lock); - si->swap_file = NULL; si->flags = 0; spin_unlock(&swap_lock); vfree(swap_map); -- 2.52.0