linux-kernel - Re: [ANNOUNCE] 5.10.162-rt78

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Date:   Fri, 20 Jan 2023 07:01:23 +0100
From:   Mike Galbraith <efault@....de>
To:     Jens Axboe <axboe@...nel.dk>,
        Salvatore Bonaccorso <carnil@...ian.org>,
        "Luis Claudio R. Goncalves" <lgoncalv@...hat.com>
Cc:     Pavel Machek <pavel@...x.de>,
        Vignesh Raghavendra <vigneshr@...com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        stable-rt <stable-rt@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Carsten Emde <C.Emde@...dl.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Daniel Wagner <daniel.wagner@...e.com>,
        Tom Zanussi <tom.zanussi@...ux.intel.com>,
        Clark Williams <williams@...hat.com>,
        Mark Gross <markgross@...nel.org>,
        Jeff Brady <jeffreyjbrady@...il.com>
Subject: Re: [ANNOUNCE] 5.10.162-rt78

On Thu, 2023-01-19 at 16:09 -0700, Jens Axboe wrote:
>
> I guess we need to twiddle that asm to deal with eg 16 bits, rather than
> attempt to backport any TIF removal patches.

Hm, 'mov' gets past the weird ass rules committee, so seems it should
be trivial for someone who speaks arm.  This built/booted once on rpi4.

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index d5bc1dbdd2fd..a4931bff8ea9 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -751,7 +760,12 @@ SYM_CODE_START_LOCAL(ret_to_user)
 	bl	trace_hardirqs_off
 #endif
 	ldr	x19, [tsk, #TSK_TI_FLAGS]
+#ifndef CONFIG_PREEMPT_RT
 	and	x2, x19, #_TIF_WORK_MASK
+#else
+	mov	x2, #_TIF_WORK_MASK
+	and	x2, x19, x2
+#endif
 	cbnz	x2, work_pending
 finish_ret_to_user:
 	user_enter_irqoff