From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 6742E3AD522 for ; Fri, 17 Jul 2026 09:17:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784279856; cv=none; b=HmynxM8TWBuSO5y3mZG09vaRb+4V27Yq0ysGKMwjDcDXbD14NRXnNTKnYlnNs275WUXGKRAHl9wLfZq18BZXSjogfaWIN1F9ZTTdSp59SQ0Uk98q+oysv0WwY9TSDMEuWPZDcdx6VIW2MsoeDpDq7aDUOm4lo1flAKJXBKhZLxc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784279856; c=relaxed/simple; bh=TcvQs6F2v9EfyD3bmkH2ZJNuDwiXRYvlBdAb+UIR3+c=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: In-Reply-To:Content-Type:Content-Disposition; b=JlPc01s/dgr9gwMBObiaUbJTrxKV7lLcuNIJHXHNMINhHAUU4rNVCUzRD4De+nfB3KF2kE/LUu5eJE0wR57h+YZNRgOYnKhCyXAiP2JI3cY51bcqPW7VQdtLi/8LFC0XYvtaneb9maYBHXtB9bZ2JG8TZ1UJNbcRswzv+t/GG44= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=YWJf5kHi; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="YWJf5kHi" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1784279852; 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: in-reply-to:in-reply-to:references:references; bh=NW+VUNQqci5Qpk0bUufyRvpeFY5npnr0jdisr26TODw=; b=YWJf5kHiWN5WoCkd2UrgPPd5a9Xl2Js1pScz0Tgw3Wa6WZ1gHkHXbnlHvN7Z+AWGCtgVan VcDXPmZbXG3br8cvRQla+jCAFLCSbLat/9jG0MRzp5AydbxjikIj9qKRUNNVdyuADjj06m K534Ii9lhHWJ8k3HKmJtMl0IEXdWnMY= Received: from mail-wr1-f70.google.com (mail-wr1-f70.google.com [209.85.221.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-155-iQyioEfcOfiVC22wM0GBFw-1; Fri, 17 Jul 2026 05:17:31 -0400 X-MC-Unique: iQyioEfcOfiVC22wM0GBFw-1 X-Mimecast-MFC-AGG-ID: iQyioEfcOfiVC22wM0GBFw_1784279850 Received: by mail-wr1-f70.google.com with SMTP id ffacd0b85a97d-472c330e555so3600456f8f.1 for ; Fri, 17 Jul 2026 02:17:30 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1784279850; x=1784884650; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:from:date:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=NW+VUNQqci5Qpk0bUufyRvpeFY5npnr0jdisr26TODw=; b=EiHuhDwki834Ptp5rFaa1L3CDt0bGj8x/sPVfvCns2FS2/65LuwaAEBmMIsYmXQvfo Y1jJAH1VWG9ujtfzRe0n+u7/0izh+IyFttyvpzNYbTrGxNF+B/q8iI6sysIBjTKtskZp A4316yDQw1McuxCeSJ+r1t/CphV1JUQp6QWscPahxhNsosLQaqNEd0DOXqJt3aJhOZf7 OS1fqtyWmTCW9ZZiT1NQCnVugYEb9MmeDhqMbUrwSVuvHVOtvrWbq8BksghRzHaQWjnm KjZqccRX+1c8tweuVc8ZuMeiPHd0kb2zKTvWGDcLBdfy2gBnBjBb4uzagrN655gQyFKK xP4Q== X-Forwarded-Encrypted: i=1; AHgh+RrPBU79xdCZEaWvnjWc8TwYDPEvNVUja2GdG1QSjSekjI5pHf/TTixHWHNb4ecFPmIbBWc6eh35V/k2/JFFlA==@lists.linux.dev X-Gm-Message-State: AOJu0YzeyxXBuQZnF9xpN2YF4MWAt14yXWWPYQ0Gx/8v+UffAqkX+gFA 6LDy72kEANA9p+BgcfyD//Nthqdb34S4fITu0PjofTRalRl/muy3J4dbGDpIqij2LJ2P3GXUlhG tkTYHCefh5FTCabB4LLDX+Uw0KThgUNojoyYacl97IKugSi7c9GrHAED/m9obCHR6zKuW X-Gm-Gg: AfdE7cmFknXVPiuXXjDOawihXpNZ8ZsamUOYw67ofqmnvPHiHSzb02JbeAXff2A8viI eYxJIZ6r1kYdhNgOKk8fmn6S1FRByzyUYvEs8BJuh6dK+ZmJ5qQcYpKFNfUFQ15+OtYS6CdtPEh eEulasSrrxDEyPJHxtMb/H4CX/Ib5jnbNV13tbent5Es9/INnUmNN/1+93O1qFIjzVeJrnYqZ2E UfkPkYA2qqi3snj8RZ1gSuISNj8QMcDI9KhhqDc+BrHsQHTRtnheh5tdaQjuTxI47qnXBCog7r7 EJW6RPf8G2BsAZ/YhypxTTboqfJUFIIG1JIyNM4Y15lx+dZm49oyZp944HKWahHjX1YGjXIMfWR uagMyPOC6jTjuG0n+TaBsKd5B X-Received: by 2002:a05:600c:1c20:b0:493:e97b:3b9c with SMTP id 5b1f17b1804b1-4954b560583mr11786575e9.29.1784279849557; Fri, 17 Jul 2026 02:17:29 -0700 (PDT) X-Received: by 2002:a05:600c:1c20:b0:493:e97b:3b9c with SMTP id 5b1f17b1804b1-4954b560583mr11786175e9.29.1784279848835; Fri, 17 Jul 2026 02:17:28 -0700 (PDT) Received: from redhat.com (IGLD-80-230-24-117.inter.net.il. [80.230.24.117]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4954a2edbe4sm34107625e9.12.2026.07.17.02.17.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 17 Jul 2026 02:17:28 -0700 (PDT) Date: Fri, 17 Jul 2026 05:17:24 -0400 From: "Michael S. Tsirkin" To: Link Lin Cc: Andrew Morton , Vlastimil Babka , David Hildenbrand , virtualization@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, prasin@google.com, rientjes@google.com, duenwen@google.com, jasowang@redhat.com, xuanzhuo@linux.alibaba.com, Ammar Faizi , jiaqiyan@google.com, ahwilkins@google.com, Greg Thelen , Alexander Duyck , jthoughton@google.com, stable@vger.kernel.org Subject: Re: [PATCH v2 2/2] virtio_balloon: avoid shrinker execution during PM suspend Message-ID: <20260717051241-mutt-send-email-mst@kernel.org> References: <20260717002311.681748-1-linkl@google.com> <20260717002311.681748-3-linkl@google.com> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: <20260717002311.681748-3-linkl@google.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: FSHfym8VQMNFhhucAxOd4vTKIjvErV2saeRdkVkv8GA_1784279850 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Fri, Jul 17, 2026 at 12:22:21AM +0000, Link Lin wrote: > During PM freeze (e.g. S4 hibernation), virtballoon_freeze() calls > remove_common() which resets the virtio device and deletes all virtqueues. > However, the balloon shrinker remains registered with core MM. > > If memory pressure occurs during S4 hibernation image creation/saving, MM > invokes virtio_balloon_shrinker_scan(), which attempts to reclaim free > pages. Although return_free_pages_to_mm() only frees pages back to MM, > reclaiming free pages under memory pressure can trigger page reporting > which might access the deleted reporting virtqueue if it is not yet > frozen, or interact with other parts of the driver in a teardown state. i feel this is the thing to fix then? not the freeing itself. > > Avoid this by adding a `suspended` flag to `struct virtio_balloon`. Set > this flag to true in virtballoon_freeze() and false in > virtballoon_restore(). Check this flag in both shrinker callbacks (scan > and count) and return 0 if the device is suspended, preventing any > shrinker execution while virtqueues are deleted. Wrap the lockless reads > in READ_ONCE() and writes in WRITE_ONCE() to prevent compiler > optimization issues and KCSAN data race warnings. so you prevented the warnings but did you fix the races? CB > > Fixes: 71019de8219b ("virtio_balloon: Add free page hinting support") > Cc: stable@vger.kernel.org > Acked-by: David Rientjes > Signed-off-by: Link Lin > --- > drivers/virtio/virtio_balloon.c | 49 +++++++++++++++++++++++++++------ > 1 file changed, 41 insertions(+), 8 deletions(-) > > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c > index 088b3a0e6c..38e1166a64 100644 > --- a/drivers/virtio/virtio_balloon.c > +++ b/drivers/virtio/virtio_balloon.c > @@ -68,6 +68,8 @@ struct virtio_balloon { > /* Prevent updating balloon when it is being canceled. */ > spinlock_t stop_update_lock; > bool stop_update; > + /* Prevent shrinker from running while device is suspended. */ > + bool suspended; > /* Bitmap to indicate if reading the related config fields are needed */ > unsigned long config_read_bitmap; > > @@ -471,9 +473,9 @@ static inline s64 towards_target(struct virtio_balloon *vb) > return target - vb->num_pages; > } > > -/* Gives back @num_to_return blocks of free pages to mm. */ > -static unsigned long return_free_pages_to_mm(struct virtio_balloon *vb, > - unsigned long num_to_return) > +/* Helper: must be called with free_page_list_lock held */ > +static unsigned long __return_free_pages_to_mm(struct virtio_balloon *vb, > + unsigned long num_to_return) > { > unsigned long num_returned = 0; > struct page *page, *next; > @@ -481,8 +483,6 @@ static unsigned long return_free_pages_to_mm(struct virtio_balloon *vb, > if (unlikely(!num_to_return)) > return 0; > > - spin_lock_irq(&vb->free_page_list_lock); > - > list_for_each_entry_safe(page, next, &vb->free_page_list, lru) { > list_del(&page->lru); > __free_pages(page, VIRTIO_BALLOON_HINT_BLOCK_ORDER); > @@ -490,11 +490,27 @@ static unsigned long return_free_pages_to_mm(struct virtio_balloon *vb, > break; > } > vb->num_free_page_blocks -= num_returned; > - spin_unlock_irq(&vb->free_page_list_lock); > > return num_returned; > } > > +/* Gives back @num_to_return blocks of free pages to mm. */ > +static unsigned long return_free_pages_to_mm(struct virtio_balloon *vb, > + unsigned long num_to_return) > +{ > + unsigned long ret; > + > + spin_lock_irq(&vb->free_page_list_lock); > + if (vb->suspended) { > + spin_unlock_irq(&vb->free_page_list_lock); > + return 0; > + } > + ret = __return_free_pages_to_mm(vb, num_to_return); > + spin_unlock_irq(&vb->free_page_list_lock); > + > + return ret; > +} > + > static void virtio_balloon_queue_free_page_work(struct virtio_balloon *vb) > { > if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) > @@ -871,6 +887,9 @@ static unsigned long virtio_balloon_shrinker_scan(struct shrinker *shrinker, > { > struct virtio_balloon *vb = shrinker->private_data; > > + if (READ_ONCE(vb->suspended)) > + return 0; > + what if vb->suspended is set right here? > return shrink_free_pages(vb, sc->nr_to_scan); > } > > @@ -879,6 +898,9 @@ static unsigned long virtio_balloon_shrinker_count(struct shrinker *shrinker, > { > struct virtio_balloon *vb = shrinker->private_data; > > + if (READ_ONCE(vb->suspended)) > + return 0; > + or here? > return vb->num_free_page_blocks * VIRTIO_BALLOON_HINT_BLOCK_PAGES; > } > > @@ -1089,8 +1111,11 @@ static void remove_common(struct virtio_balloon *vb) > update_balloon_size(vb); > > /* There might be free pages that are being reported: release them. */ > - if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) > - return_free_pages_to_mm(vb, ULONG_MAX); > + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) { > + spin_lock_irq(&vb->free_page_list_lock); > + __return_free_pages_to_mm(vb, ULONG_MAX); > + spin_unlock_irq(&vb->free_page_list_lock); this is remove, taking locks seems futile - if something will acquire the lock here, we will be in trouble. > + } > > /* Now we reset the device so we can clean up the queues. */ > virtio_reset_device(vb->vdev); > @@ -1133,6 +1158,10 @@ static int virtballoon_freeze(struct virtio_device *vdev) > * The workqueue is already frozen by the PM core before this > * function is called. > */ > + spin_lock_irq(&vb->free_page_list_lock); > + WRITE_ONCE(vb->suspended, true); > + spin_unlock_irq(&vb->free_page_list_lock); > + > remove_common(vb); > return 0; > } > @@ -1148,6 +1177,10 @@ static int virtballoon_restore(struct virtio_device *vdev) > > virtio_device_ready(vdev); > > + spin_lock_irq(&vb->free_page_list_lock); > + WRITE_ONCE(vb->suspended, false); > + spin_unlock_irq(&vb->free_page_list_lock); > + > if (towards_target(vb)) > virtballoon_changed(vdev); > update_balloon_size(vb); > -- > 2.55.0.229.g6434b31f56-goog