linux-kernel - [PATCH RT] x86/mm/pat: disable preemption __split_large_page() after spin

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Message-ID: <20181213164430.mggilzfjgr5retz6@linutronix.de>
Date:   Thu, 13 Dec 2018 17:44:31 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     linux-rt-users@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>, stable-rt@...r.kernel.org
Subject: [PATCH RT] x86/mm/pat: disable preemption __split_large_page() after
 spin_lock()

Commit "x86/mm/pat: Disable preemption around __flush_tlb_all()" added a
warning if __flush_tlb_all() is invoked in preemptible context. On !RT
the warning does not trigger because a spin lock is acquired which
disables preemption. On RT the spin lock does not disable preemption and
so the warning is seen.

Disable preemption to avoid the warning in __flush_tlb_all().

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 arch/x86/mm/pageattr.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index e2d4b25c7aa44..abbe3e93ec266 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -687,6 +687,7 @@ __split_large_page(struct cpa_data *cpa, pte_t *kpte, unsigned long address,
 	pgprot_t ref_prot;
 
 	spin_lock(&pgd_lock);
+	preempt_disable();
 	/*
 	 * Check for races, another CPU might have split this page
 	 * up for us already:
@@ -694,6 +695,7 @@ __split_large_page(struct cpa_data *cpa, pte_t *kpte, unsigned long address,
 	tmp = _lookup_address_cpa(cpa, address, &level);
 	if (tmp != kpte) {
 		spin_unlock(&pgd_lock);
+		preempt_enable();
 		return 1;
 	}
 
@@ -727,6 +729,7 @@ __split_large_page(struct cpa_data *cpa, pte_t *kpte, unsigned long address,
 
 	default:
 		spin_unlock(&pgd_lock);
+		preempt_enable();
 		return 1;
 	}
 
@@ -764,6 +767,7 @@ __split_large_page(struct cpa_data *cpa, pte_t *kpte, unsigned long address,
 	 * going on.
 	 */
 	__flush_tlb_all();
+	preempt_enable();
 	spin_unlock(&pgd_lock);
 
 	return 0;
-- 
2.20.0