[PATCH 4.9 28/32] virtio_balloon: fix another race between migration and ballooning

Greg Kroah-Hartman
2018-08-04T09:06:25Z

From: Jiang Biao <jiang.biao2@zte.com.cn>

commit 89da619bc18d79bca5304724c11d4ba3b67ce2c6 upstream.

Kernel panic when with high memory pressure, calltrace looks like,

PID: 21439 TASK: ffff881be3afedd0 CPU: 16 COMMAND: "java"
#0 [ffff881ec7ed7630] machine_kexec at ffffffff81059beb
#1 [ffff881ec7ed7690] __crash_kexec at ffffffff81105942
#2 [ffff881ec7ed7760] crash_kexec at ffffffff81105a30
#3 [ffff881ec7ed7778] oops_end at ffffffff816902c8
#4 [ffff881ec7ed77a0] no_context at ffffffff8167ff46
#5 [ffff881ec7ed77f0] __bad_area_nosemaphore at ffffffff8167ffdc
#6 [ffff881ec7ed7838] __node_set at ffffffff81680300
#7 [ffff881ec7ed7860] __do_page_fault at ffffffff8169320f
#8 [ffff881ec7ed78c0] do_page_fault at ffffffff816932b5
#9 [ffff881ec7ed78f0] page_fault at ffffffff8168f4c8
[exception RIP: _raw_spin_lock_irqsave+47]
RIP: ffffffff8168edef RSP: ffff881ec7ed79a8 RFLAGS: 00010046
RAX: 0000000000000246 RBX: ffffea0019740d00 RCX: ffff881ec7ed7fd8
RDX: 0000000000020000 RSI: 0000000000000016 RDI: 0000000000000008
RBP: ffff881ec7ed79a8 R8: 0000000000000246 R9: 000000000001a098
R10: ffff88107ffda000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000008 R14: ffff881ec7ed7a80 R15: ffff881be3afedd0
ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018

It happens in the pagefault and results in double pagefault
during compacting pages when memory allocation fails.

Analysed the vmcore, the page leads to second pagefault is corrupted
with _mapcount=-256, but private=0.

It's caused by the race between migration and ballooning, and lock
missing in virtballoon_migratepage() of virtio_balloon driver.
This patch fix the bug.

Fixes: e22504296d4f64f ("virtio_balloon: introduce migration primitives to balloon pages")
Cc: stable@vger.kernel.org
Signed-off-by: Jiang Biao <jiang.biao2@zte.com.cn>
Signed-off-by: Huang Chong <huang.chong@zte.com.cn>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/virtio/virtio_balloon.c | 2 ++
1 file changed, 2 insertions(+)

--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -493,7 +493,9 @@ static int virtballoon_migratepage(struc
tell_host(vb, vb->inflate_vq);

/* balloon's page migration 2nd step -- deflate "page" */
+ spin_lock_irqsave(&vb_dev_info->pages_lock, flags);
balloon_page_delete(page);
+ spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags);
vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
set_page_pfns(vb, vb->pfns, page);
tell_host(vb, vb->deflate_vq);