[PATCH 7/9] x86/lbr: correctly check for kthreads

From: Mark Rutland <mark.rutland@arm.com>
To: linux-kernel@vger.kernel.org
Cc: ak@linux.intel.com, akpm@linux-foundation.org,
	bigeasy@linutronix.de, bp@suse.de, catalin.marinas@arm.com,
	davem@davemloft.net, hch@lst.de, kan.liang@intel.com,
	mark.rutland@arm.com, mingo@kernel.org, peterz@infradead.org,
	riel@surriel.com, will@kernel.org
Subject: [PATCH 7/9] x86/lbr: correctly check for kthreads
Date: Wed, 14 Aug 2019 11:41:29 +0100	[thread overview]
Message-ID: <20190814104131.20190-8-mark.rutland@arm.com> (raw)
In-Reply-To: <20190814104131.20190-1-mark.rutland@arm.com>

The x86 lbr branch_type() 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@arm.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
---
 arch/x86/events/intel/lbr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c
index 6f814a27416b..ed2b7e57a249 100644
--- a/arch/x86/events/intel/lbr.c
+++ b/arch/x86/events/intel/lbr.c
@@ -857,7 +857,7 @@ static int branch_type(unsigned long from, unsigned long to, int abort)
 		 * can happen if measuring at the user level only
 		 * and we interrupt in a kernel thread, e.g., idle.
 		 */
-		if (!current->mm)
+		if (is_kthread(current))
 			return X86_BR_NONE;
 
 		/* may fail if text not present */
-- 
2.11.0

