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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1785161197; 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-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=4yGYb4251xen6xq86IV6E6mB7obBsI6jDmsaNtiaKQw=; b=Ol4EjBnMG3jAVqaTNBrQNftF0n45q6z3fLWxqc8Mp8aara4iUzUCTVxMThAlxS640iHEHw LP1XunNzgeje1Er9j984M+KsfbsdxP1b0NUYKLD0QOxDCzu+1dV73d5Hl3AjLjxIQvdlJ8 X42wigqlOFa6/7nrIdgszuh1/qKrRHw= From: Baoquan He To: linux-mm@kvack.org Cc: akpm@linux-foundation.org, chrisl@kernel.org, nphamcs@gmail.com, kasong@tencent.com, baohua@kernel.org, youngjun.park@lge.com, hannes@cmpxchg.org, yosry@kernel.org, david@kernel.org, shikemeng@huaweicloud.com, chengming.zhou@linux.dev, linux-kernel@vger.kernel.org, Baoquan He Subject: [RFC PATCH 10/11] mm, swap: defer xswap shrink to workqueue to avoid lock recursion Date: Mon, 27 Jul 2026 22:05:01 +0800 Message-ID: <20260727140503.1060918-9-baoquan.he@linux.dev> In-Reply-To: <20260727140503.1060918-1-baoquan.he@linux.dev> References: <20260727135029.1059441-1-baoquan.he@linux.dev> <20260727140503.1060918-1-baoquan.he@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-type: text/plain Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 1CB0E1C000C X-Stat-Signature: ymhfowccx6qt6csdssu1yju8h7osu486 X-HE-Tag: 1785161198-797548 X-HE-Meta: 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 G6W6vOdT EHPp8DQhV+Z5E2WJxiBcqkMIQ00sABbdBtxVnrkXvQ2EDhlmbEVeQ1UsZJMriZTdQItX4k5NDA1hQLFyvVfo/7aqPVohoAd8Fh+lU6reMv8MNjikkJihwNNfIKoUTMWOJsSg7vOpmu5JXXmAW+quFGEnLxMQNf79iTE5mspL0CHUC0VDgxA6SbXgbfUHLtrIccaEUXTj45aT1zIkaiTZWU9bndyPZ1d4hcYGCbXvBVO7SVK1wYATHTYLePWgExPxdULW8sotVFLwQT/LXZjVhFySq2fbZ7N2P/uHPyNqXbD04DZk= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: xswap_try_shrink() was called directly from __free_cluster() while holding ci->lock. The shrink path calls xswap_unmap_clusters() which unmaps vmalloc pages backing cluster_info, and on return swap_cache_del_folio() tries swap_cluster_unlock(ci) on the now- unmapped address — crashing on a not-present page. Replace direct calls with schedule_work() so shrink runs in an independent workqueue context where no cluster locks are held. Use cancel_work_sync() during swapoff to ensure no pending shrink work races with the VM area teardown. Signed-off-by: Baoquan He --- include/linux/swap.h | 1 + mm/swapfile.c | 18 ++++++++++++------ 2 files changed, 13 insertions(+), 6 deletions(-) diff --git a/include/linux/swap.h b/include/linux/swap.h index ebcd5eaa7924..ebae01fbd100 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -255,6 +255,7 @@ struct swap_info_struct { unsigned long nr_clusters_mapped; /* currently mapped cluster count */ unsigned long nr_free_tail; /* contiguous free clusters at tail */ struct dentry *debugfs_entry; /* debugfs: type_max_clusters */ + struct work_struct xswap_shrink_work; /* deferred shrink trigger */ #endif struct list_head free_clusters; /* free clusters list */ struct list_head full_clusters; /* full clusters list */ diff --git a/mm/swapfile.c b/mm/swapfile.c index af62981506d3..b41ff2c594fc 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -127,11 +127,8 @@ static ssize_t xswap_max_clusters_write(struct file *file, spin_unlock(&swap_lock); } - /* - * Lowering the ceiling may make tail clusters eligible for - * shrinking. Trigger an immediate check. - */ - xswap_try_shrink(si); + /* Shrink trigger: lowering the ceiling may free tail clusters. */ + schedule_work(&si->xswap_shrink_work); return count; } @@ -726,7 +723,7 @@ static void __free_cluster(struct swap_info_struct *si, struct swap_cluster_info ci->order = 0; #ifdef CONFIG_XSWAP xswap_update_free_tail(si, ci - si->cluster_info); - xswap_try_shrink(si); + schedule_work(&si->xswap_shrink_work); #endif } @@ -3236,6 +3233,7 @@ static void free_swap_cluster_info(struct swap_info_struct *si) #ifdef CONFIG_XSWAP if (si->flags & SWP_XSWAP) { xswap_debugfs_del(si); + cancel_work_sync(&si->xswap_shrink_work); /* Unmap all mapped clusters and free the VM_SPARSE area */ if (si->nr_clusters_mapped > 0) xswap_unmap_clusters(si, 0, si->nr_clusters_mapped); @@ -4030,6 +4028,13 @@ static void xswap_trim_free_tail(struct swap_info_struct *si, unsigned long idx) WRITE_ONCE(si->nr_free_tail, nr_mapped - idx - 1); } +static void xswap_shrink_work_fn(struct work_struct *work) +{ + struct swap_info_struct *si = container_of(work, + struct swap_info_struct, xswap_shrink_work); + xswap_try_shrink(si); +} + /* * Try to shrink the cluster_info tail. Uses si->nr_free_tail which * is maintained incrementally during alloc/free — no scanning needed. @@ -4137,6 +4142,7 @@ static int setup_swap_clusters_info(struct swap_info_struct *si, /* All mapped clusters except cluster 0 are free at the tail */ si->nr_free_tail = si->nr_clusters_mapped - 1; + INIT_WORK(&si->xswap_shrink_work, xswap_shrink_work_fn); xswap_debugfs_add(si); return 0; -- 2.54.0