linux-kernel - [tip: core/entry] ARM: Snapshot thread flags

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Date:   Fri, 26 Nov 2021 20:22:57 -0000
From:   "tip-bot2 for Mark Rutland" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Mark Rutland <mark.rutland@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Russell King <linux@...linux.org.uk>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: core/entry] ARM: Snapshot thread flags

The following commit has been merged into the core/entry branch of tip:

Commit-ID:     3fe5dec062dfc8344356823457f5f43e0730c074
Gitweb:        https://git.kernel.org/tip/3fe5dec062dfc8344356823457f5f43e0730c074
Author:        Mark Rutland <mark.rutland@....com>
AuthorDate:    Wed, 17 Nov 2021 16:30:43 
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Fri, 26 Nov 2021 21:20:13 +01:00

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, a snapshot of the flags has to be taken prior to
using them. Some places already use READ_ONCE() for that, others do not.

Convert them all to the new flag accessor helpers.

Signed-off-by: Mark Rutland <mark.rutland@....com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Acked-by: Paul E. McKenney <paulmck@...nel.org>
Cc: Russell King <linux@...linux.org.uk>
Link: https://lore.kernel.org/r/20211117163050.53986-6-mark.rutland@arm.com
---
 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 a41e27a..c532a60 100644
--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c
@@ -631,7 +631,7 @@ 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 ea81e89..adbb381 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);
 	}