linux-kernel - [RFC PATCH 05/10] arm: snapshot thread flags

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Message-Id: <20210609122001.18277-6-mark.rutland@arm.com>
Date:   Wed,  9 Jun 2021 13:19:56 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     linux-kernel@...r.kernel.org
Cc:     benh@...nel.crashing.org, boqun.feng@...il.com, bp@...en8.de,
        catalin.marinas@....com, dvyukov@...gle.com, elver@...gle.com,
        ink@...assic.park.msu.ru, jonas@...thpole.se,
        juri.lelli@...hat.com, linux@...linux.org.uk, luto@...nel.org,
        mark.rutland@....com, mattst88@...il.com, mingo@...hat.com,
        monstr@...str.eu, mpe@...erman.id.au, paulmck@...nel.org,
        paulus@...ba.org, peterz@...radead.org, rth@...ddle.net,
        shorne@...il.com, stefan.kristiansson@...nalahti.fi,
        tglx@...utronix.de, vincent.guittot@...aro.org, will@...nel.org
Subject: [RFC PATCH 05/10] arm: snapshot thread flags

Some thread flags can be set remotely, and so even when IRQs are
disabled, the flags can change under our feet. Generally this is
unlikely to cause a problem in practice, but it is somewhat unsound, and
KCSAN will legitimately warn that there is a data race.

To avoid such issues, we should snapshot the flags prior to using them.
Let's use the new helpers to do so on arm.

Signed-off-by: Mark Rutland <mark.rutland@....com>
Cc: Russell King <linux@...linux.org.uk>
---
 arch/arm/kernel/signal.c | 2 +-
 arch/arm/mm/alignment.c  | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
index a3a38d0a4c85..40c1178bd8c2 100644
--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c
@@ -674,7 +674,7 @@ do_work_pending(struct pt_regs *regs, unsigned int thread_flags, int syscall)
 			}
 		}
 		local_irq_disable();
-		thread_flags = current_thread_info()->flags;
+		thread_flags = read_thread_flags();
 	} while (thread_flags & _TIF_WORK_MASK);
 	return 0;
 }
diff --git a/arch/arm/mm/alignment.c b/arch/arm/mm/alignment.c
index ea81e89e7740..adbb3817d0be 100644
--- a/arch/arm/mm/alignment.c
+++ b/arch/arm/mm/alignment.c
@@ -990,7 +990,7 @@ do_alignment(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 		 * there is no work pending for this thread.
 		 */
 		raw_local_irq_disable();
-		if (!(current_thread_info()->flags & _TIF_WORK_MASK))
+		if (!(read_thread_flags() & _TIF_WORK_MASK))
 			set_cr(cr_no_alignment);
 	}
 
-- 
2.11.0