The patch titled
Subject: io-mapping: don't disable preempt on RT in io_mapping_map_atomic_wc().
has been added to the -mm mm-unstable branch. Its filename is
io-mapping-dont-disable-preempt-on-rt-in-io_mapping_map_atomic_wc.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/io-mapping-dont-disable-preempt-on-rt-in-io_mapping_map_atomic_wc.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Subject: io-mapping: don't disable preempt on RT in io_mapping_map_atomic_wc().
Date: Fri, 10 Mar 2023 17:29:05 +0100
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@xxxxxxxxxxxxx
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Reported-by: Richard Weinberger <richard.weinberger@xxxxxxxxx>
Link: https://lore.kernel.org/CAFLxGvw0WMxaMqYqJ5WgvVSbKHq2D2xcXTOgMCpgq9nDC-MWTQ@xxxxxxxxxxxxxx
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
--- a/include/linux/io-mapping.h~io-mapping-dont-disable-preempt-on-rt-in-io_mapping_map_atomic_wc
+++ a/include/linux/io-mapping.h
@@ -69,7 +69,10 @@ io_mapping_map_atomic_wc(struct io_mappi
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 *va
{
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 *va
{
io_mapping_unmap(vaddr);
pagefault_enable();
- preempt_enable();
+ if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+ preempt_enable();
+ else
+ migrate_enable();
}
static inline void __iomem *
_
Patches currently in -mm which might be from bigeasy@xxxxxxxxxxxxx are
io-mapping-dont-disable-preempt-on-rt-in-io_mapping_map_atomic_wc.patch
