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author | Paolo Bonzini <pbonzini@redhat.com> | 2016-11-17 17:55:45 +0300 |
---|---|---|
committer | Radim Krčmář <rkrcmar@redhat.com> | 2016-11-19 21:04:17 +0300 |
commit | 22583f0d9c85e60c9860bc8a0ebff59fe08be6d7 (patch) | |
tree | 54128e22130c2f3b349cf67fd972c94fe77e95ef /virt | |
parent | e3fd9a93a12a1020067a676e826877623cee8e2b (diff) | |
download | linux-22583f0d9c85e60c9860bc8a0ebff59fe08be6d7.tar.xz |
KVM: async_pf: avoid recursive flushing of work items
This was reported by syzkaller:
[ INFO: possible recursive locking detected ]
4.9.0-rc4+ #49 Not tainted
---------------------------------------------
kworker/2:1/5658 is trying to acquire lock:
([ 1644.769018] (&work->work)
[< inline >] list_empty include/linux/compiler.h:243
[<ffffffff8128dd60>] flush_work+0x0/0x660 kernel/workqueue.c:1511
but task is already holding lock:
([ 1644.769018] (&work->work)
[<ffffffff812916ab>] process_one_work+0x94b/0x1900 kernel/workqueue.c:2093
stack backtrace:
CPU: 2 PID: 5658 Comm: kworker/2:1 Not tainted 4.9.0-rc4+ #49
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Workqueue: events async_pf_execute
ffff8800676ff630 ffffffff81c2e46b ffffffff8485b930 ffff88006b1fc480
0000000000000000 ffffffff8485b930 ffff8800676ff7e0 ffffffff81339b27
ffff8800676ff7e8 0000000000000046 ffff88006b1fcce8 ffff88006b1fccf0
Call Trace:
...
[<ffffffff8128ddf3>] flush_work+0x93/0x660 kernel/workqueue.c:2846
[<ffffffff812954ea>] __cancel_work_timer+0x17a/0x410 kernel/workqueue.c:2916
[<ffffffff81295797>] cancel_work_sync+0x17/0x20 kernel/workqueue.c:2951
[<ffffffff81073037>] kvm_clear_async_pf_completion_queue+0xd7/0x400 virt/kvm/async_pf.c:126
[< inline >] kvm_free_vcpus arch/x86/kvm/x86.c:7841
[<ffffffff810b728d>] kvm_arch_destroy_vm+0x23d/0x620 arch/x86/kvm/x86.c:7946
[< inline >] kvm_destroy_vm virt/kvm/kvm_main.c:731
[<ffffffff8105914e>] kvm_put_kvm+0x40e/0x790 virt/kvm/kvm_main.c:752
[<ffffffff81072b3d>] async_pf_execute+0x23d/0x4f0 virt/kvm/async_pf.c:111
[<ffffffff8129175c>] process_one_work+0x9fc/0x1900 kernel/workqueue.c:2096
[<ffffffff8129274f>] worker_thread+0xef/0x1480 kernel/workqueue.c:2230
[<ffffffff812a5a94>] kthread+0x244/0x2d0 kernel/kthread.c:209
[<ffffffff831f102a>] ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:433
The reason is that kvm_put_kvm is causing the destruction of the VM, but
the page fault is still on the ->queue list. The ->queue list is owned
by the VCPU, not by the work items, so we cannot just add list_del to
the work item.
Instead, use work->vcpu to note async page faults that have been resolved
and will be processed through the done list. There is no need to flush
those.
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Diffstat (limited to 'virt')
-rw-r--r-- | virt/kvm/async_pf.c | 13 |
1 files changed, 12 insertions, 1 deletions
diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c index 8035cc1eb955..efeceb0a222d 100644 --- a/virt/kvm/async_pf.c +++ b/virt/kvm/async_pf.c @@ -91,6 +91,7 @@ static void async_pf_execute(struct work_struct *work) spin_lock(&vcpu->async_pf.lock); list_add_tail(&apf->link, &vcpu->async_pf.done); + apf->vcpu = NULL; spin_unlock(&vcpu->async_pf.lock); /* @@ -113,6 +114,8 @@ static void async_pf_execute(struct work_struct *work) void kvm_clear_async_pf_completion_queue(struct kvm_vcpu *vcpu) { + spin_lock(&vcpu->async_pf.lock); + /* cancel outstanding work queue item */ while (!list_empty(&vcpu->async_pf.queue)) { struct kvm_async_pf *work = @@ -120,6 +123,14 @@ void kvm_clear_async_pf_completion_queue(struct kvm_vcpu *vcpu) typeof(*work), queue); list_del(&work->queue); + /* + * We know it's present in vcpu->async_pf.done, do + * nothing here. + */ + if (!work->vcpu) + continue; + + spin_unlock(&vcpu->async_pf.lock); #ifdef CONFIG_KVM_ASYNC_PF_SYNC flush_work(&work->work); #else @@ -129,9 +140,9 @@ void kvm_clear_async_pf_completion_queue(struct kvm_vcpu *vcpu) kmem_cache_free(async_pf_cache, work); } #endif + spin_lock(&vcpu->async_pf.lock); } - spin_lock(&vcpu->async_pf.lock); while (!list_empty(&vcpu->async_pf.done)) { struct kvm_async_pf *work = list_first_entry(&vcpu->async_pf.done, |