linux-kernel - [PATCH] arm64: abort counter_read_on_cpu() when irqs

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Message-Id: <20201113155328.4194-1-ionela.voinescu@arm.com>
Date:   Fri, 13 Nov 2020 15:53:28 +0000
From:   Ionela Voinescu <ionela.voinescu@....com>
To:     catalin.marinas@....com, mark.rutland@....com,
        sudeep.holla@....com, will@...nel.org
Cc:     morten.rasmussen@....com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, ionela.voinescu@....com
Subject: [PATCH] arm64: abort counter_read_on_cpu() when irqs_disabled()

Given that smp_call_function_single() can deadlock when interrupts are
disabled, abort the SMP call if irqs_disabled(). This scenario is
currently not possible given the function's uses, but safeguard this for
potential future uses.

Signed-off-by: Ionela Voinescu <ionela.voinescu@....com>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Will Deacon <will@...nel.org>
---
 arch/arm64/kernel/topology.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index 3a083a9a8ef2..e387188741f2 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -343,7 +343,11 @@ static void cpu_read_constcnt(void *val)
 static inline
 int counters_read_on_cpu(int cpu, smp_call_func_t func, u64 *val)
 {
-	if (!cpu_has_amu_feat(cpu))
+	/*
+	 * Abort call on counterless CPU or when interrupts are
+	 * disabled - can lead to deadlock in smp sync call.
+	 */
+	if (!cpu_has_amu_feat(cpu) || unlikely(irqs_disabled()))
 		return -EOPNOTSUPP;
 
 	smp_call_function_single(cpu, func, val, 1);
-- 
2.17.1