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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Tue, 23 Jan 2024 12:56:21 +0100
Subject: [PATCH] arm: Disable FAST_GUP on PREEMPT_RT if HIGHPTE is also
enabled.
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.8/older/patches-6.8.2-rt11.tar.xz
gup_pgd_range() is invoked with disabled interrupts and invokes
__kmap_local_page_prot() via pte_offset_map(), gup_p4d_range().
With HIGHPTE enabled, __kmap_local_page_prot() invokes kmap_high_get()
which uses a spinlock_t via lock_kmap_any(). This leads to an
sleeping-while-atomic error on PREEMPT_RT because spinlock_t becomes a
sleeping lock and must not be acquired in atomic context.
The loop in map_new_virtual() uses wait_queue_head_t for wake up which
also is using a spinlock_t.
Limit HAVE_FAST_GUP additionaly to remain disabled on PREEMPT_RT with
HIGHPTE enabled.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
arch/arm/Kconfig | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -98,7 +98,7 @@ config ARM
select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE
select HAVE_EFFICIENT_UNALIGNED_ACCESS if (CPU_V6 || CPU_V6K || CPU_V7) && MMU
select HAVE_EXIT_THREAD
- select HAVE_FAST_GUP if ARM_LPAE
+ select HAVE_FAST_GUP if ARM_LPAE && !(PREEMPT_RT && HIGHPTE)
select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
select HAVE_FUNCTION_ERROR_INJECTION
select HAVE_FUNCTION_GRAPH_TRACER
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