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[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: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260717002311.681748-3-linkl@google.com> 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