kmap_atomic() disables preemption and pagefaults for historical
reasons. The conversion to kmap_local(), 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 kmap_atomic() semantics are
problematic due to the implicit disabling of preemption which makes it
impossible to acquire 'sleeping' spinlocks within the kmap 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.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
---
include/linux/highmem-internal.h | 27 ++++++++++++++++++++++-----
1 file changed, 22 insertions(+), 5 deletions(-)
diff --git a/include/linux/highmem-internal.h b/include/linux/highmem-internal.h
index 7902c7d8b55f9..4aa1031d3e4c3 100644
--- a/include/linux/highmem-internal.h
+++ b/include/linux/highmem-internal.h
@@ -90,7 +90,11 @@ static inline void __kunmap_local(void *vaddr)
static inline void *kmap_atomic_prot(struct page *page, pgprot_t prot)
{
- preempt_disable();
+ if (IS_ENABLED(CONFIG_PREEMPT_RT))
+ migrate_disable();
+ else
+ preempt_disable();
+
pagefault_disable();
return __kmap_local_page_prot(page, prot);
}
@@ -102,7 +106,11 @@ static inline void *kmap_atomic(struct page *page)
static inline void *kmap_atomic_pfn(unsigned long pfn)
{
- preempt_disable();
+ if (IS_ENABLED(CONFIG_PREEMPT_RT))
+ migrate_disable();
+ else
+ preempt_disable();
+
pagefault_disable();
return __kmap_local_pfn_prot(pfn, kmap_prot);
}
@@ -111,7 +119,10 @@ static inline void __kunmap_atomic(void *addr)
{
kunmap_local_indexed(addr);
pagefault_enable();
- preempt_enable();
+ if (IS_ENABLED(CONFIG_PREEMPT_RT))
+ migrate_enable();
+ else
+ preempt_enable();
}
unsigned int __nr_free_highpages(void);
@@ -179,7 +190,10 @@ static inline void __kunmap_local(void *addr)
static inline void *kmap_atomic(struct page *page)
{
- preempt_disable();
+ if (IS_ENABLED(CONFIG_PREEMPT_RT))
+ migrate_disable();
+ else
+ preempt_disable();
pagefault_disable();
return page_address(page);
}
@@ -200,7 +214,10 @@ static inline void __kunmap_atomic(void *addr)
kunmap_flush_on_unmap(addr);
#endif
pagefault_enable();
- preempt_enable();
+ if (IS_ENABLED(CONFIG_PREEMPT_RT))
+ migrate_enable();
+ else
+ preempt_enable();
}
static inline unsigned int nr_free_highpages(void) { return 0; }
--
2.32.0
