linux-kernel - [PATCH 4/9] arm/perf: correctly check for kthreads

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Date:   Wed, 14 Aug 2019 11:41:26 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     linux-kernel@...r.kernel.org
Cc:     ak@...ux.intel.com, akpm@...ux-foundation.org,
        bigeasy@...utronix.de, bp@...e.de, catalin.marinas@....com,
        davem@...emloft.net, hch@....de, kan.liang@...el.com,
        mark.rutland@....com, mingo@...nel.org, peterz@...radead.org,
        riel@...riel.com, will@...nel.org
Subject: [PATCH 4/9] arm/perf: correctly check for kthreads

The arm perf_callchain_user() functions looks at current->mm,
apparently to determine whether the thread is a kthread without any
valid user context.

In general, a non-NULL current->mm doesn't imply that current is a
kthread, as kthreads can install an mm via use_mm(), and so it's
preferable to use is_kthread() to determine whether a thread is a
kthread.

For consistency, let's use is_kthread() here.

Signed-off-by: Mark Rutland <mark.rutland@....com>
Cc: Will Deacon <will@...nel.org>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
---
 arch/arm/kernel/perf_callchain.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/kernel/perf_callchain.c b/arch/arm/kernel/perf_callchain.c
index 3b69a76d341e..5c920f2c46a8 100644
--- a/arch/arm/kernel/perf_callchain.c
+++ b/arch/arm/kernel/perf_callchain.c
@@ -71,7 +71,7 @@ perf_callchain_user(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs
 
 	perf_callchain_store(entry, regs->ARM_pc);
 
-	if (!current->mm)
+	if (is_kthread(current))
 		return;
 
 	tail = (struct frame_tail __user *)regs->ARM_fp - 1;
-- 
2.11.0