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From 0e993c3a89f8f2098b4d23ca8b34c327850ee6fb Mon Sep 17 00:00:00 2001
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Fri, 10 Mar 2023 17:29:05 +0100
Subject: [PATCH 53/64] io-mapping: don't disable preempt on RT in
io_mapping_map_atomic_wc().
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.1/older/patches-6.1.82-rt27.tar.xz
io_mapping_map_atomic_wc() disables preemption and pagefaults for
historical reasons. The conversion to io_mapping_map_local_wc(), which
only disables migration, cannot be done wholesale because quite some call
sites need to be updated to accommodate with the changed semantics.
On PREEMPT_RT enabled kernels the io_mapping_map_atomic_wc() semantics are
problematic due to the implicit disabling of preemption which makes it
impossible to acquire 'sleeping' spinlocks within the mapped atomic
sections.
PREEMPT_RT replaces the preempt_disable() with a migrate_disable() for
more than a decade. It could be argued that this is a justification to do
this unconditionally, but PREEMPT_RT covers only a limited number of
architectures and it disables some functionality which limits the coverage
further.
Limit the replacement to PREEMPT_RT for now. This is also done
kmap_atomic().
Link: https://lkml.kernel.org/r/20230310162905.O57Pj7hh@linutronix.de
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reported-by: Richard Weinberger <richard.weinberger@gmail.com>
Link: https://lore.kernel.org/CAFLxGvw0WMxaMqYqJ5WgvVSbKHq2D2xcXTOgMCpgq9nDC-MWTQ@mail.gmail.com
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
(cherry picked from commit 7eb16f23b9a415f062db22739e59bb144e0b24ab)
Signed-off-by: Clark Williams <clark.williams@gmail.com>
---
include/linux/io-mapping.h | 20 ++++++++++++++++----
1 file changed, 16 insertions(+), 4 deletions(-)
diff --git a/include/linux/io-mapping.h b/include/linux/io-mapping.h
index 66a774d2710e..b08532b8fba7 100644
--- a/include/linux/io-mapping.h
+++ b/include/linux/io-mapping.h
@@ -69,7 +69,10 @@ io_mapping_map_atomic_wc(struct io_mapping *mapping,
BUG_ON(offset >= mapping->size);
phys_addr = mapping->base + offset;
- preempt_disable();
+ if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+ preempt_disable();
+ else
+ migrate_disable();
pagefault_disable();
return __iomap_local_pfn_prot(PHYS_PFN(phys_addr), mapping->prot);
}
@@ -79,7 +82,10 @@ io_mapping_unmap_atomic(void __iomem *vaddr)
{
kunmap_local_indexed((void __force *)vaddr);
pagefault_enable();
- preempt_enable();
+ if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+ preempt_enable();
+ else
+ migrate_enable();
}
static inline void __iomem *
@@ -162,7 +168,10 @@ static inline void __iomem *
io_mapping_map_atomic_wc(struct io_mapping *mapping,
unsigned long offset)
{
- preempt_disable();
+ if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+ preempt_disable();
+ else
+ migrate_disable();
pagefault_disable();
return io_mapping_map_wc(mapping, offset, PAGE_SIZE);
}
@@ -172,7 +181,10 @@ io_mapping_unmap_atomic(void __iomem *vaddr)
{
io_mapping_unmap(vaddr);
pagefault_enable();
- preempt_enable();
+ if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+ preempt_enable();
+ else
+ migrate_enable();
}
static inline void __iomem *
--
2.44.0
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