From nobody Sun May 19 12:26:28 2024 Received: from mail-pj1-f74.google.com (mail-pj1-f74.google.com [209.85.216.74]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 720BB13E057 for ; Tue, 23 Apr 2024 19:16:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.74 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713899813; cv=none; b=ogO7seu0cB31TqTLkHANOk8Uyzo6EyR/36YBBfGMSZHDlD0MAwjy3Jr9hcP/HCzobw9cXGu/pIfSgOTaUCLIYgjKgnU/6IY4WW/4yredxxcacOp+1VeJCDVv5cR6wyrBmj8gmATKdZZaHGrieq55OE7d4I5zhKbhIJ/QqPS4zUk= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713899813; c=relaxed/simple; bh=rKJ3l5PngsMhhUsgGiBJulPEoC22NhzF9omTbh59/TI=; h=Date:Mime-Version:Message-ID:Subject:From:To:Cc:Content-Type; b=rS6QNCwQjWZRbJwDl3XDOJlnECbjbCKEH1lB+taRwCahhja7rIlez4Y8+C3BQLqDI01/TY0L8JrYDrTRUGkGioBbVkdQhPDDyAyn0SnaTNsyaCS8/f5NJJZS+0LdV6fwmZ00T0xH0iv6JM5rFc2vCGeZzzMyqmohlPWnqaSUE38= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=cnyJSpdt; arc=none smtp.client-ip=209.85.216.74 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="cnyJSpdt" Received: by mail-pj1-f74.google.com with SMTP id 98e67ed59e1d1-2ae63694954so2069885a91.3 for ; Tue, 23 Apr 2024 12:16:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1713899812; x=1714504612; darn=vger.kernel.org; h=cc:to:from:subject:message-id:mime-version:date:reply-to:from:to:cc :subject:date:message-id:reply-to; bh=8B8BJDQiGUAbI0tZGCCPFyop6LA8Xy8bkwpS740fWe0=; b=cnyJSpdtTy358I3qXwRZOR0UkyGFGx7akqv6eOLaC4uZZgfLJ6vdUg6NKbsrU/hmgE 3oRc87Nls3lX5EXG/tMfHyRrZ2PASYUXnwMXX48jTeYkzl2EGifKYzv+0T+BVnWpUIWX ikuqSatc4QLoPC5nsoo8ygJru5Cs6YquwMs0hQsEtt5UEC9DvdLgPZU6//0cSqbUn/X2 C+g3sb5CUjC2CsYPpTYeVn9aoW2Jeb5rRq27m1tU0Fd1NpOuUp1taAjHYD6ApByS22zF E/CTHYuuvWPN7itfVNtwnK8OVN6UBh/K1AHpo1TYouPulANPreXtfm4LCs7sW8XgzhI3 Iy4g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1713899812; x=1714504612; h=cc:to:from:subject:message-id:mime-version:date:reply-to :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=8B8BJDQiGUAbI0tZGCCPFyop6LA8Xy8bkwpS740fWe0=; b=LEMwXW/4H4SO1LAEX87MO+hzBOyp0tqO72+RDKDd3b3SoAfDYWdCpHEqx4ZLcT0vqu qDf25zCZEPbaT49FO59YhfESzepZjOf7BsgV0jXSLP7GCgiVBSviWS4F2WT0Kb6htAbl BF2cRY0lsBKqx2k1SQCbcKpRJoFzrm13m2xFTu/IhGCkneNYVHZ4vWcdmBzVwujE9TEL t6RRoqMgAsicgXWE52Ws124sppSVm63tIQ6pjTdvHUnCG+ncmDyr5rK5oKofhtiHYzWV oxUnOPHhSpKMh9UqlMorgrZ3Qe4BGwMrKYNpi5/xMIQFScdLYa8iVHegwnSgAZS2D8s6 kMGg== X-Forwarded-Encrypted: i=1; AJvYcCWeofZUBRzPkktxRDk4Jm/AOPZJtoAyDxSn3L6HPIBHhXUPjcfMeE5v8Arv/TPickKZ7zaGJFPnXCVntbR5K/3nO8JZyM4r47Sim3b5 X-Gm-Message-State: AOJu0YzlXcNX/dysGU+g4O8SIwvz+Z+UHQ/ME8nvY6Ch/n4cHWXkKlIh 954uWpWCU0v9vvBVdqZiT56ESdHkWlArEokK73YVWeb5FXcx2CwBXoKiennJMfCn1UEEA9jVPOr JLQ== X-Google-Smtp-Source: AGHT+IHc2Pkewcf/fjEyx1Ej8IWpt/3GzaBNYp2bJhAmBKboXze10z/yAFFif1JOzokxw7TZwp+xbvaMBRk= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a17:90a:8a95:b0:2a2:ff01:dd7c with SMTP id x21-20020a17090a8a9500b002a2ff01dd7cmr1330pjn.8.1713899811718; Tue, 23 Apr 2024 12:16:51 -0700 (PDT) Reply-To: Sean Christopherson Date: Tue, 23 Apr 2024 12:16:49 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 X-Mailer: git-send-email 2.44.0.769.g3c40516874-goog Message-ID: <20240423191649.2885257-1-seanjc@google.com> Subject: [PATCH] Revert "KVM: async_pf: avoid recursive flushing of work items" From: Sean Christopherson To: Paolo Bonzini Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Xu Yilun , Sean Christopherson Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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 Signed-off-by: Sean Christopherson --- virt/kvm/async_pf.c | 13 +------------ 1 file changed, 1 insertion(+), 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 =3D list_empty(&vcpu->async_pf.done); list_add_tail(&apf->link, &vcpu->async_pf.done); - apf->vcpu =3D NULL; spin_unlock(&vcpu->async_pf.lock); =20 /* @@ -120,8 +119,6 @@ static void kvm_flush_and_free_async_pf_work(struct kvm= _async_pf *work) =20 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 =3D @@ -129,23 +126,15 @@ void kvm_clear_async_pf_completion_queue(struct kvm_v= cpu *vcpu) typeof(*work), queue); list_del(&work->queue); =20 - /* - * 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); } =20 + spin_lock(&vcpu->async_pf.lock); while (!list_empty(&vcpu->async_pf.done)) { struct kvm_async_pf *work =3D list_first_entry(&vcpu->async_pf.done, base-commit: d2ea9fd98cca88b4724b4515cd4d40452f78caa8 --=20 2.44.0.769.g3c40516874-goog