Wei Wang
2017-Oct-12 02:36 UTC
[PATCH] virtio: avoid possible OOM lockup at virtballoon_oom_notify()
On 10/10/2017 06:47 PM, Tetsuo Handa wrote:> 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. Thus, do not wait for vb->balloon_lock mutex if > leak_balloon() is called from out_of_memory(). > > 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 > > Signed-off-by: Tetsuo Handa <penguin-kernel at I-love.SAKURA.ne.jp>I think we could also use 'bool wait' to let the OOM use the traditional leak_balloon code path, which doesn't need memory allocation from xb_preload(). That is, inside leak_balloon(), we can have use_sg = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_SG) & wait; Reviewed-by: Wei Wang <wei.w.wang at intel.com>> --- > drivers/virtio/virtio_balloon.c | 16 +++++++++++----- > 1 file changed, 11 insertions(+), 5 deletions(-) > > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c > index f0b3a0b..03e6078 100644 > --- a/drivers/virtio/virtio_balloon.c > +++ b/drivers/virtio/virtio_balloon.c > @@ -192,7 +192,7 @@ static void release_pages_balloon(struct virtio_balloon *vb, > } > } > > -static unsigned leak_balloon(struct virtio_balloon *vb, size_t num) > +static unsigned leak_balloon(struct virtio_balloon *vb, size_t num, bool wait) > { > unsigned num_freed_pages; > struct page *page; > @@ -202,7 +202,13 @@ static unsigned leak_balloon(struct virtio_balloon *vb, size_t num) > /* We can only do one array worth at a time. */ > num = min(num, ARRAY_SIZE(vb->pfns)); > > - mutex_lock(&vb->balloon_lock); > + if (wait) > + mutex_lock(&vb->balloon_lock); > + else if (!mutex_trylock(&vb->balloon_lock)) { > + pr_info("virtio_balloon: Unable to release %lu pages due to lock contention.\n", > + (unsigned long) min(num, (size_t)vb->num_pages)); > + return 0; > + } > /* We can't release more pages than taken */ > num = min(num, (size_t)vb->num_pages); > for (vb->num_pfns = 0; vb->num_pfns < num; > @@ -367,7 +373,7 @@ static int virtballoon_oom_notify(struct notifier_block *self, > return NOTIFY_OK; > > freed = parm; > - num_freed_pages = leak_balloon(vb, oom_pages); > + num_freed_pages = leak_balloon(vb, oom_pages, false); > update_balloon_size(vb); > *freed += num_freed_pages; > > @@ -395,7 +401,7 @@ static void update_balloon_size_func(struct work_struct *work) > if (diff > 0) > diff -= fill_balloon(vb, diff); > else if (diff < 0) > - diff += leak_balloon(vb, -diff); > + diff += leak_balloon(vb, -diff, true); > update_balloon_size(vb); > > if (diff) > @@ -597,7 +603,7 @@ static void remove_common(struct virtio_balloon *vb) > { > /* There might be pages left in the balloon: free them. */ > while (vb->num_pages) > - leak_balloon(vb, vb->num_pages); > + leak_balloon(vb, vb->num_pages, true); > update_balloon_size(vb); > > /* Now we reset the device so we can clean up the queues. */
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