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| author | Sean Christopherson <seanjc@google.com> | 2024-04-23 21:16:49 +0200 |
|---|---|---|
| committer | Sean Christopherson <seanjc@google.com> | 2024-06-03 17:55:55 +0200 |
| commit | 778c350eb580a497c9da2a01e314fe12674cb66a (patch) | |
| tree | c918315eeefabed11c0b3c1843cf070f882f95de /virt | |
| parent | KVM: Update halt polling documentation to note that KVM has 4 module params (diff) | |
| download | linux-778c350eb580a497c9da2a01e314fe12674cb66a.tar.xz linux-778c350eb580a497c9da2a01e314fe12674cb66a.zip | |
Revert "KVM: async_pf: avoid recursive flushing of work items"
Now that KVM does NOT gift async #PF workers a "struct kvm" reference,
don't bother skipping "done" workers when flushing/canceling queued
workers, as the deadlock that was being fudged around can no longer occur.
When workers, i.e. async_pf_execute(), were gifted a referenced, it was
possible for a worker to put the last reference and trigger VM destruction,
i.e. trigger flushing of a workqueue from a worker in said workqueue.
Note, there is no actual lock, the deadlock was that a worker will be
stuck waiting for itself (the workqueue code simulates a lock/unlock via
lock_map_{acquire,release}()).
Skipping "done" workers isn't problematic per se, but using work->vcpu as
a "done" flag is confusing, e.g. it's not clear that async_pf.lock is
acquired to protect the work->vcpu, NOT the processing of async_pf.queue
(which is protected by vcpu->mutex).
This reverts commit 22583f0d9c85e60c9860bc8a0ebff59fe08be6d7.
Suggested-by: Xu Yilun <yilun.xu@linux.intel.com>
Link: https://lore.kernel.org/r/20240423191649.2885257-1-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Diffstat (limited to 'virt')
| -rw-r--r-- | virt/kvm/async_pf.c | 13 |
1 files changed, 1 insertions, 12 deletions
diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c index 99a63bad0306..0ee4816b079a 100644 --- a/virt/kvm/async_pf.c +++ b/virt/kvm/async_pf.c @@ -80,7 +80,6 @@ static void async_pf_execute(struct work_struct *work) spin_lock(&vcpu->async_pf.lock); first = list_empty(&vcpu->async_pf.done); list_add_tail(&apf->link, &vcpu->async_pf.done); - apf->vcpu = NULL; spin_unlock(&vcpu->async_pf.lock); /* @@ -120,8 +119,6 @@ static void kvm_flush_and_free_async_pf_work(struct kvm_async_pf *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 = @@ -129,23 +126,15 @@ 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 if (cancel_work_sync(&work->work)) 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, |