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[79.177.145.168]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4954a2b87c6sm212015435e9.7.2026.07.18.07.16.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 18 Jul 2026 07:16:57 -0700 (PDT) Date: Sat, 18 Jul 2026 10:16:54 -0400 From: "Michael S. Tsirkin" To: Andrew Morton Cc: mm-commits@vger.kernel.org, xuanzhuo@linux.alibaba.com, vbabka@kernel.org, stable@vger.kernel.org, rientjes@google.com, jthoughton@google.com, jiaqiyan@google.com, jasowang@redhat.com, gthelen@google.com, david@redhat.com, david@kernel.org, alexander.duyck@gmail.com, linkl@google.com Subject: Re: + virtio_balloon-avoid-shrinker-execution-during-pm-suspend.patch added to mm-new branch Message-ID: <20260718101506-mutt-send-email-mst@kernel.org> References: <20260718003902.B6DD51F000E9@smtp.kernel.org> 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: <20260718003902.B6DD51F000E9@smtp.kernel.org> On Fri, Jul 17, 2026 at 05:39:02PM -0700, Andrew Morton wrote: > > The patch titled > Subject: virtio_balloon: avoid shrinker execution during PM suspend > has been added to the -mm mm-new branch. Its filename is > virtio_balloon-avoid-shrinker-execution-during-pm-suspend.patch > > This patch will shortly appear at > https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/virtio_balloon-avoid-shrinker-execution-during-pm-suspend.patch > > This patch will later appear in the mm-new branch at > git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm > > Note, mm-new is a provisional staging ground for work-in-progress > patches, and acceptance into mm-new is a notification for others take > notice and to finish up reviews. Please do not hesitate to respond to > review feedback and post updated versions to replace or incrementally > fixup patches in mm-new. > > The mm-new branch of mm.git is not included in linux-next > > If a few days of testing in mm-new is successful, the patch will me moved > into mm.git's mm-unstable branch, which is included in linux-next > > Before you just go and hit "reply", please: > a) Consider who else should be cc'ed > b) Prefer to cc a suitable mailing list as well > c) Ideally: find the original patch on the mailing list and do a > reply-to-all to that, adding suitable additional cc's > > *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** > > The -mm tree is included into linux-next via various > branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm > and is updated there most days > > ------------------------------------------------------ > From: Link Lin > Subject: virtio_balloon: avoid shrinker execution during PM suspend > Date: Fri, 17 Jul 2026 00:22:21 +0000 > > 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. > > 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. > > Link: https://lore.kernel.org/20260717002311.681748-3-linkl@google.com > Fixes: 71019de8219b ("virtio_balloon: Add free page hinting support") > Signed-off-by: Link Lin > Acked-by: David Rientjes > Suggested-by: James Houghton > Cc: Michael S. Tsirkin > Cc: Alexander Duyck > Cc: David Hildenbrand > Cc: Greg Thelen > Cc: Jason Wang > Cc: Jiaqi Yan > Cc: Vlastimil Babka > Cc: Xuan Zhuo > Cc: David Hildenbrand > Cc: > Signed-off-by: Andrew Morton This patch generated quite a bit of discussion. Are you sure it makes sense to keep it in mm as is? In particular: > --- > > drivers/virtio/virtio_balloon.c | 49 +++++++++++++++++++++++++----- > 1 file changed, 41 insertions(+), 8 deletions(-) > > --- a/drivers/virtio/virtio_balloon.c~virtio_balloon-avoid-shrinker-execution-during-pm-suspend > +++ a/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 > 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_t > 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_t > 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_shri > { > struct virtio_balloon *vb = shrinker->private_data; > > + if (READ_ONCE(vb->suspended)) > + return 0; > + what if suspended bit is set right afterwards? Seems racy. > return shrink_free_pages(vb, sc->nr_to_scan); > } > > @@ -879,6 +898,9 @@ static unsigned long virtio_balloon_shri > { > struct virtio_balloon *vb = shrinker->private_data; > > + if (READ_ONCE(vb->suspended)) > + return 0; > + > return vb->num_free_page_blocks * VIRTIO_BALLOON_HINT_BLOCK_PAGES; > } > > @@ -1086,8 +1108,11 @@ static void remove_common(struct virtio_ > 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); > + } > > /* Now we reset the device so we can clean up the queues. */ > virtio_reset_device(vb->vdev); > @@ -1130,6 +1155,10 @@ static int virtballoon_freeze(struct vir > * 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; > } > @@ -1145,6 +1174,10 @@ static int virtballoon_restore(struct vi > > 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); > _ > > Patches currently in -mm which might be from linkl@google.com are > > mm-page_reporting-use-system_freezable_wq-to-fix-uaf-during-suspend.patch > virtio_balloon-avoid-shrinker-execution-during-pm-suspend.patch