From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-176.mta1.migadu.com (out-176.mta1.migadu.com [95.215.58.176]) (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 D20F02F5A29 for ; Mon, 27 Jul 2026 14:06:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.176 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785161212; cv=none; b=tMLRRpBFAAkPAxUUxf51d8VPZ6WuJPYygDSe+n6AAt4xn10nPP2XXfpmchZ45//C0UbdcKITZUdRbSFxn5SXfbRZON20kvn4/xQASJrT2bNsBy3SUPH3cLviIpfEa9cvkuci3Wl6WU0gUnM/wUWzlNX/Hk6ydL7TpUNiwPT4z38= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785161212; c=relaxed/simple; bh=Sy4ooY3tOOWfVPz4xjVGxTKx089BqBTsdHgFjL+5D2A=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-type; b=NlfsdEqYzfNF6IqYnpOQ3oyJ0aAlqB3MIJrVnyAcOJ+idIscDalnzfzIvdsQW5wRNzB5PU+nSqx943Wh7q7R/+FjGY8bOsmW7LXTbT0UR8Hc88afffuvsX6RmvFTLzojEr0G2vWBZ0KccF86+xbr3uupsgJN0Vhnpo7O86Uvd2U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=xL1htqHG; arc=none smtp.client-ip=95.215.58.176 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="xL1htqHG" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1785161208; 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-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=IwPLUDcYtzirJbTxv7cVnoW3Ob/U1PfUpNFV/nBTnqo=; b=xL1htqHG48CwyZbQnfU77hWkxzflKln+ZJeLE8qKJdsAz0dpvUhRxaEqk6Z+Omk+w4ISN8 j9kMjG78FSyg1JZJjxBgPVAYM7QgZYRLs3V0f7lSG+08H3+kZix6Dq7cJEXOL3qKpUuLeZ No9LYhDp61B7VrF9xPvkNRh1emhNu3I= 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 11/11] mm, swap: serialize xswap map/unmap with a mutex Date: Mon, 27 Jul 2026 22:05:02 +0800 Message-ID: <20260727140503.1060918-10-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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-type: text/plain Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT Concurrent xswap grow operations race on vm_area_map_pages(), triggering WARN_ON(!pte_none) in the vmap page table walk when one thread sees a PTE already set by another. The -EBUSY safety net catches it but the warning is noisy and unavoidable without serialization. Add a per-device mutex (xswap_lock) held across xswap_map_clusters and xswap_unmap_clusters so that only one thread can modify the VM_SPARSE page table at a time. The shrink path is already deferred to a workqueue so it does not contend with itself. Signed-off-by: Baoquan He --- include/linux/swap.h | 1 + mm/swapfile.c | 17 +++++++++++++++-- 2 files changed, 16 insertions(+), 2 deletions(-) diff --git a/include/linux/swap.h b/include/linux/swap.h index ebae01fbd100..b0fe0475bba7 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -256,6 +256,7 @@ struct swap_info_struct { 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 */ + struct mutex xswap_lock; /* serialize map/unmap operations */ #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 b41ff2c594fc..89c6a6b03a9d 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -3773,11 +3773,14 @@ static int xswap_map_clusters(struct swap_info_struct *si, struct page **pages; unsigned long i; + mutex_lock(&si->xswap_lock); + if (vm_start >= vm_end) { /* All requested clusters fall within already-mapped pages. */ for (i = start_idx; i < start_idx + nr; i++) spin_lock_init(&si->cluster_info[i].lock); WRITE_ONCE(si->nr_clusters_mapped, start_idx + nr); + mutex_unlock(&si->xswap_lock); return 0; } @@ -3842,6 +3845,7 @@ static int xswap_map_clusters(struct swap_info_struct *si, * Pairs with READ_ONCE() in shrink/grow paths. */ WRITE_ONCE(si->nr_clusters_mapped, start_idx + nr); + mutex_unlock(&si->xswap_lock); return 0; fail_nounmap: @@ -3862,6 +3866,7 @@ static int xswap_map_clusters(struct swap_info_struct *si, spin_lock_init(&si->cluster_info[i].lock); WRITE_ONCE(si->nr_clusters_mapped, start_idx + nr); + mutex_unlock(&si->xswap_lock); return 0; fail: @@ -3871,6 +3876,7 @@ static int xswap_map_clusters(struct swap_info_struct *si, __free_page(pages[i]); } kfree(pages); + mutex_unlock(&si->xswap_lock); return -ENOMEM; } @@ -3910,8 +3916,12 @@ static void xswap_unmap_clusters(struct swap_info_struct *si, struct xswap_page_data xpd; int i; - if (vm_start >= vm_end) + mutex_lock(&si->xswap_lock); + + if (vm_start >= vm_end) { + mutex_unlock(&si->xswap_lock); goto out; + } size = vm_end - vm_start; npages = size >> PAGE_SHIFT; @@ -3937,10 +3947,12 @@ static void xswap_unmap_clusters(struct swap_info_struct *si, __free_page(xpd.pages[i]); kfree(xpd.pages); } + + mutex_unlock(&si->xswap_lock); +out: /* * Pairs with READ_ONCE() in shrink/grow paths. */ - out: WRITE_ONCE(si->nr_clusters_mapped, start_idx); } @@ -4142,6 +4154,7 @@ 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; + mutex_init(&si->xswap_lock); INIT_WORK(&si->xswap_shrink_work, xswap_shrink_work_fn); xswap_debugfs_add(si); return 0; -- 2.54.0