On Fri, Dec 01, 2017 at 11:31:08PM +1100, Michael Ellerman wrote:
> "Michael S. Tsirkin" <mst@xxxxxxxxxx> writes:
>
> > fill_balloon doing memory allocations under balloon_lock
> > can cause a deadlock when leak_balloon is called from
> > virtballoon_oom_notify and tries to take same lock.
> >
> > To fix, split page allocation and enqueue and do allocations outside the lock.
> >
> > Here's a detailed analysis of the deadlock by Tetsuo Handa:
> >
> > In leak_balloon(), mutex_lock(&vb->balloon_lock) is called in order to
> > serialize against fill_balloon(). But in fill_balloon(),
> > alloc_page(GFP_HIGHUSER[_MOVABLE] | __GFP_NOMEMALLOC | __GFP_NORETRY) is
> > called with vb->balloon_lock mutex held. Since GFP_HIGHUSER[_MOVABLE]
> > implies __GFP_DIRECT_RECLAIM | __GFP_IO | __GFP_FS, despite __GFP_NORETRY
> > is specified, this allocation attempt might indirectly depend on somebody
> > else's __GFP_DIRECT_RECLAIM memory allocation. And such indirect
> > __GFP_DIRECT_RECLAIM memory allocation might call leak_balloon() via
> > virtballoon_oom_notify() via blocking_notifier_call_chain() callback via
> > out_of_memory() when it reached __alloc_pages_may_oom() and held oom_lock
> > mutex. Since vb->balloon_lock mutex is already held by fill_balloon(), it
> > will cause OOM lockup.
> >
> > Thread1 Thread2
> > fill_balloon()
> > takes a balloon_lock
> > balloon_page_enqueue()
> > alloc_page(GFP_HIGHUSER_MOVABLE)
> > direct reclaim (__GFP_FS context) takes a fs lock
> > waits for that fs lock alloc_page(GFP_NOFS)
> > __alloc_pages_may_oom()
> > takes the oom_lock
> > out_of_memory()
> > blocking_notifier_call_chain()
> > leak_balloon()
> > tries to take that balloon_lock and deadlocks
> >
> > Reported-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> > Cc: Michal Hocko <mhocko@xxxxxxxx>
> > Cc: Wei Wang <wei.w.wang@xxxxxxxxx>
> > Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> >
> > drivers/virtio/virtio_balloon.c | 24 +++++++++++++++++++-----
> > include/linux/balloon_compaction.h | 35 ++++++++++++++++++++++++++++++++++-
> > mm/balloon_compaction.c | 28 +++++++++++++++++++++-------
> > 3 files changed, 74 insertions(+), 13 deletions(-)
>
>
> Somehow this commit seems to be killing powerpc guests.
>
> The symptom is that the first page (64K) of the guests memory gets over
> written with zeroes, which is where our interrupt handlers are, so the
> system rapidly locks up due to illegal instructions in the illegal
> instruction handler.
>
> There seems to be some element of a race, because it doesn't always
> crash. Sometimes I can boot to a shell, but not often. When it does
> happen it's fairly late in boot, but before I get to a shell.
>
> I had a few bisects go off into the weeds due to the intermittent
> nature. But once I realised that I changed my script to boot 5 times
> before declaring a kernel good, and that bisected straight here.
>
> I can also revert this commit on v4.15-rc1 and everything's fine again -
> I got through ~250 boots with that kernel.
>
> So I'm pretty sure this commit is triggering/exposing/causing the bug.
>
> The other data point is that the page that's overwritten is mapped read
> only in the guest kernel. So either the guest kernel is writing to it in
> real mode (MMU off), or the hypervisor/DMA is doing it.
>
> I haven't isolated if it's host kernel/qemu version dependent, at the
> moment I'm just using distro packaged versions of both.
>
> Anyway I'll try and dig further into it on Monday, but I thought I'd let
> you know in case this is a known bug with a fix in the pipeline, or
> rings any bells or whatever.
>
> cheers
Thanks for the report!
A fix was just posted:
virtio_balloon: fix increment of vb->num_pfns in fill_balloon()
Would appreciate testing.
>
> > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> > index f0b3a0b..7960746 100644
> > --- a/drivers/virtio/virtio_balloon.c
> > +++ b/drivers/virtio/virtio_balloon.c
> > @@ -143,16 +143,17 @@ static void set_page_pfns(struct virtio_balloon *vb,
> >
> > static unsigned fill_balloon(struct virtio_balloon *vb, size_t num)
> > {
> > - struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;
> > unsigned num_allocated_pages;
> > + unsigned num_pfns;
> > + struct page *page;
> > + LIST_HEAD(pages);
> >
> > /* We can only do one array worth at a time. */
> > num = min(num, ARRAY_SIZE(vb->pfns));
> >
> > - mutex_lock(&vb->balloon_lock);
> > - for (vb->num_pfns = 0; vb->num_pfns < num;
> > - vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
> > - struct page *page = balloon_page_enqueue(vb_dev_info);
> > + for (num_pfns = 0; num_pfns < num;
> > + num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
> > + struct page *page = balloon_page_alloc();
> >
> > if (!page) {
> > dev_info_ratelimited(&vb->vdev->dev,
> > @@ -162,6 +163,19 @@ static unsigned fill_balloon(struct virtio_balloon *vb, size_t num)
> > msleep(200);
> > break;
> > }
> > +
> > + balloon_page_push(&pages, page);
> > + }
> > +
> > + mutex_lock(&vb->balloon_lock);
> > +
> > + vb->num_pfns = 0;
> > +
> > + while ((page = balloon_page_pop(&pages))) {
> > + balloon_page_enqueue(&vb->vb_dev_info, page);
> > +
> > + vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE;
> > +
> > set_page_pfns(vb, vb->pfns + vb->num_pfns, page);
> > vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE;
> > if (!virtio_has_feature(vb->vdev,
> > diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h
> > index fbbe6da..c4c8df9 100644
> > --- a/include/linux/balloon_compaction.h
> > +++ b/include/linux/balloon_compaction.h
> > @@ -50,6 +50,7 @@
> > #include <linux/gfp.h>
> > #include <linux/err.h>
> > #include <linux/fs.h>
> > +#include <linux/list.h>
> >
> > /*
> > * Balloon device information descriptor.
> > @@ -67,7 +68,9 @@ struct balloon_dev_info {
> > struct inode *inode;
> > };
> >
> > -extern struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info);
> > +extern struct page *balloon_page_alloc(void);
> > +extern void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
> > + struct page *page);
> > extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info);
> >
> > static inline void balloon_devinfo_init(struct balloon_dev_info *balloon)
> > @@ -89,6 +92,36 @@ extern int balloon_page_migrate(struct address_space *mapping,
> > struct page *page, enum migrate_mode mode);
> >
> > /*
> > + * balloon_page_push - insert a page into a page list.
> > + * @head : pointer to list
> > + * @page : page to be added
> > + *
> > + * Caller must ensure the page is private and protect the list.
> > + */
> > +static inline void balloon_page_push(struct list_head *pages, struct page *page)
> > +{
> > + list_add(&page->lru, pages);
> > +}
> > +
> > +/*
> > + * balloon_page_pop - remove a page from a page list.
> > + * @head : pointer to list
> > + * @page : page to be added
> > + *
> > + * Caller must ensure the page is private and protect the list.
> > + */
> > +static inline struct page *balloon_page_pop(struct list_head *pages)
> > +{
> > + struct page *page = list_first_entry_or_null(pages, struct page, lru);
> > +
> > + if (!page)
> > + return NULL;
> > +
> > + list_del(&page->lru);
> > + return page;
> > +}
> > +
> > +/*
> > * balloon_page_insert - insert a page into the balloon's page list and make
> > * the page->private assignment accordingly.
> > * @balloon : pointer to balloon device
> > diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
> > index 68d2892..ef858d5 100644
> > --- a/mm/balloon_compaction.c
> > +++ b/mm/balloon_compaction.c
> > @@ -11,22 +11,37 @@
> > #include <linux/balloon_compaction.h>
> >
> > /*
> > + * balloon_page_alloc - allocates a new page for insertion into the balloon
> > + * page list.
> > + *
> > + * Driver must call it to properly allocate a new enlisted balloon page.
> > + * Driver must call balloon_page_enqueue before definitively removing it from
> > + * the guest system. This function returns the page address for the recently
> > + * allocated page or NULL in the case we fail to allocate a new page this turn.
> > + */
> > +struct page *balloon_page_alloc(void)
> > +{
> > + struct page *page = alloc_page(balloon_mapping_gfp_mask() |
> > + __GFP_NOMEMALLOC | __GFP_NORETRY);
> > + return page;
> > +}
> > +EXPORT_SYMBOL_GPL(balloon_page_alloc);
> > +
> > +/*
> > * balloon_page_enqueue - allocates a new page and inserts it into the balloon
> > * page list.
> > * @b_dev_info: balloon device descriptor where we will insert a new page to
> > + * @page: new page to enqueue - allocated using balloon_page_alloc.
> > *
> > - * Driver must call it to properly allocate a new enlisted balloon page
> > + * Driver must call it to properly enqueue a new allocated balloon page
> > * before definitively removing it from the guest system.
> > * This function returns the page address for the recently enqueued page or
> > * NULL in the case we fail to allocate a new page this turn.
> > */
> > -struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info)
> > +void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
> > + struct page *page)
> > {
> > unsigned long flags;
> > - struct page *page = alloc_page(balloon_mapping_gfp_mask() |
> > - __GFP_NOMEMALLOC | __GFP_NORETRY);
> > - if (!page)
> > - return NULL;
> >
> > /*
> > * Block others from accessing the 'page' when we get around to
> > @@ -39,7 +54,6 @@ struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info)
> > __count_vm_event(BALLOON_INFLATE);
> > spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
> > unlock_page(page);
> > - return page;
> > }
> > EXPORT_SYMBOL_GPL(balloon_page_enqueue);
> >
> > --
> > MST
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