linux-kernel - [PATCH] KVM: Deal with nested sleeps in kvm_vcpu

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Message-ID: <20221130161946.3254953-1-spm@google.com>
Date:   Wed, 30 Nov 2022 16:19:46 +0000
From:   Space Meyer <spm@...gle.com>
To:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     pbonzini@...hat.com, kpsingh@...nel.org,
        Space Meyer <spm@...gle.com>
Subject: [PATCH] KVM: Deal with nested sleeps in kvm_vcpu_block()

Previously this code assumed nothing would mess with current->state
between the set_current_state() and schedule(). However the call to
kvm_vcpu_check_block() in between might end up requiring locks or other
actions, which would change current->state. A similar pattern was
described in the "The problem with nested sleeping primitives" LWN
article[0].

[0] https://lwn.net/Articles/628628

Signed-off-by: Space Meyer <spm@...gle.com>
---
 virt/kvm/kvm_main.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index fab4d37905785..64e10d73f2a92 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -32,6 +32,7 @@
 #include <linux/sched/signal.h>
 #include <linux/sched/mm.h>
 #include <linux/sched/stat.h>
+#include <linux/wait.h>
 #include <linux/cpumask.h>
 #include <linux/smp.h>
 #include <linux/anon_inodes.h>
@@ -3426,6 +3427,7 @@ static int kvm_vcpu_check_block(struct kvm_vcpu *vcpu)
  */
 bool kvm_vcpu_block(struct kvm_vcpu *vcpu)
 {
+	DEFINE_WAIT_FUNC(vcpu_block_wait, woken_wake_function);
 	struct rcuwait *wait = kvm_arch_vcpu_get_wait(vcpu);
 	bool waited = false;
 
@@ -3437,13 +3439,11 @@ bool kvm_vcpu_block(struct kvm_vcpu *vcpu)
 	preempt_enable();
 
 	for (;;) {
-		set_current_state(TASK_INTERRUPTIBLE);
-
 		if (kvm_vcpu_check_block(vcpu) < 0)
 			break;
 
 		waited = true;
-		schedule();
+		wait_woken(&vcpu_block_wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
 	}
 
 	preempt_disable();
-- 
2.38.1.584.g0f3c55d4c2-goog