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SubjectRe: atomic copy_from_user?
On Mon, Dec 22, 2003 at 03:55:06PM -0500, Rob Love wrote:
> On Mon, 2003-12-22 at 13:26, Joe Korty wrote:
>
> > Shouldn't the dec_prempt_count() in kunmap_atomic() be followed
> > by a preempt_check_resched()???
>
> Probably.
>
> Actually, dec_preempt_count() ought to call preempt_check_resched()
> itself. In the case of !CONFIG_PREEMPT, that call would simply optimize
> away.
>
> Attached patch is against 2.6.0.
>
> Rob Love
>
>
> linux/preempt.h | 1 +
> 1 files changed, 1 insertion(+)
>
> diff -urN include/linux/preempt.h.orig include/linux/preempt.h
> --- include/linux/preempt.h.orig 2003-12-22 15:53:11.329113296 -0500
> +++ include/linux/preempt.h 2003-12-22 15:53:51.314034664 -0500
> @@ -18,6 +18,7 @@
> #define dec_preempt_count() \
> do { \
> preempt_count()--; \
> + preempt_check_resched(); \
> } while (0)
>
> #ifdef CONFIG_PREEMPT


I am guessing that nowdays even when preemption is disabled one can
find preempt_count still being used somewhere. Otherwise it would be
better to replace all uses of inc_preempt_count() with
preempt_disable() and dec_preempt_count() with preempt_enable().

Joe

diff -ura base/arch/i386/mm/highmem.c new/arch/i386/mm/highmem.c
--- base/arch/i386/mm/highmem.c 2003-12-17 21:58:56.000000000 -0500
+++ new/arch/i386/mm/highmem.c 2003-12-22 16:16:27.000000000 -0500
@@ -30,7 +30,7 @@
enum fixed_addresses idx;
unsigned long vaddr;

- inc_preempt_count();
+ preempt_disable();
if (page < highmem_start_page)
return page_address(page);

@@ -53,7 +53,7 @@
enum fixed_addresses idx = type + KM_TYPE_NR*smp_processor_id();

if (vaddr < FIXADDR_START) { // FIXME
- dec_preempt_count();
+ preempt_enable();
return;
}

@@ -68,7 +68,7 @@
__flush_tlb_one(vaddr);
#endif

- dec_preempt_count();
+ preempt_enable();
}

struct page *kmap_atomic_to_page(void *ptr)
diff -ura base/arch/mips/mm/highmem.c new/arch/mips/mm/highmem.c
--- base/arch/mips/mm/highmem.c 2003-12-17 21:58:28.000000000 -0500
+++ new/arch/mips/mm/highmem.c 2003-12-22 16:17:28.000000000 -0500
@@ -40,7 +40,7 @@
enum fixed_addresses idx;
unsigned long vaddr;

- inc_preempt_count();
+ preempt_disable();
if (page < highmem_start_page)
return page_address(page);

@@ -63,7 +63,7 @@
enum fixed_addresses idx = type + KM_TYPE_NR*smp_processor_id();

if (vaddr < FIXADDR_START) { // FIXME
- dec_preempt_count();
+ preempt_enable();
return;
}

@@ -78,7 +78,7 @@
local_flush_tlb_one(vaddr);
#endif

- dec_preempt_count();
+ preempt_enable();
}

struct page *kmap_atomic_to_page(void *ptr)
diff -ura base/arch/sparc/mm/highmem.c new/arch/sparc/mm/highmem.c
--- base/arch/sparc/mm/highmem.c 2003-12-17 21:58:28.000000000 -0500
+++ new/arch/sparc/mm/highmem.c 2003-12-22 16:17:02.000000000 -0500
@@ -33,7 +33,7 @@
unsigned long idx;
unsigned long vaddr;

- inc_preempt_count();
+ preempt_disable();
if (page < highmem_start_page)
return page_address(page);

@@ -68,7 +68,7 @@
unsigned long idx = type + KM_TYPE_NR*smp_processor_id();

if (vaddr < fix_kmap_begin) { // FIXME
- dec_preempt_count();
+ preempt_enable();
return;
}

@@ -95,5 +95,5 @@
flush_tlb_all();
#endif
#endif
- dec_preempt_count();
+ preempt_enable();
}
diff -ura base/include/asm-ppc/highmem.h new/include/asm-ppc/highmem.h
--- base/include/asm-ppc/highmem.h 2003-12-17 21:59:45.000000000 -0500
+++ new/include/asm-ppc/highmem.h 2003-12-22 16:18:05.000000000 -0500
@@ -81,7 +81,7 @@
unsigned int idx;
unsigned long vaddr;

- inc_preempt_count();
+ preempt_disable();
if (page < highmem_start_page)
return page_address(page);

@@ -104,7 +104,7 @@
unsigned int idx = type + KM_TYPE_NR*smp_processor_id();

if (vaddr < KMAP_FIX_BEGIN) { // FIXME
- dec_preempt_count();
+ preempt_disable();
return;
}

@@ -118,7 +118,7 @@
pte_clear(kmap_pte+idx);
flush_tlb_page(0, vaddr);
#endif
- dec_preempt_count();
+ preempt_enable();
}

static inline struct page *kmap_atomic_to_page(void *ptr)
-
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