linux-kernel - [PATCH] KVM: x86: Move kzalloc out of atomic context on PREEMPT

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Date:   Thu, 19 May 2022 17:02:18 +0800
From:   Yajun Deng <yajun.deng@...ux.dev>
To:     pbonzini@...hat.com, seanjc@...gle.com, vkuznets@...hat.com,
        wanpengli@...cent.com, jmattson@...gle.com, joro@...tes.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com
Cc:     x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Yajun Deng <yajun.deng@...ux.dev>
Subject: [PATCH] KVM: x86: Move kzalloc out of atomic context on PREEMPT_RT

The memory allocator is fully preemptible and therefore cannot
be invoked from truly atomic contexts.

See Documentation/locking/locktypes.rst (line: 470)

Add raw_spin_unlock() before memory allocation and raw_spin_lock()
after it.

Signed-off-by: Yajun Deng <yajun.deng@...ux.dev>
---
 arch/x86/kernel/kvm.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index d0bb2b3fb305..8f8ec9bbd847 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -205,7 +205,9 @@ void kvm_async_pf_task_wake(u32 token)
 		 * async PF was not yet handled.
 		 * Add dummy entry for the token.
 		 */
-		n = kzalloc(sizeof(*n), GFP_ATOMIC);
+		raw_spin_unlock(&b->lock);
+		n = kzalloc(sizeof(*n), GFP_KERNEL);
+		raw_spin_lock(&b->lock);
 		if (!n) {
 			/*
 			 * Allocation failed! Busy wait while other cpu
-- 
2.25.1