On Thu, 7 Dec 2006, Linux Kernel Mailing List wrote:
Gitweb: http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=a866374aecc90c7d90619727ccd851ac096b2fc7
Commit: a866374aecc90c7d90619727ccd851ac096b2fc7
Parent: 6edaf68a87d17570790fd55f0c451a29ec1d6703
Author: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
AuthorDate: Wed Dec 6 20:32:20 2006 -0800
Committer: Linus Torvalds <torvalds@xxxxxxxxxxxxxx>
CommitDate: Thu Dec 7 08:39:21 2006 -0800
[PATCH] mm: pagefault_{disable,enable}()
Introduce pagefault_{disable,enable}() and use these where previously we did
manual preempt increments/decrements to make the pagefault handler do the
atomic thing.
Currently they still rely on the increased preempt count, but do not rely on
the disabled preemption, this might go away in the future.
(NOTE: the extra barrier() in pagefault_disable might fix some holes on
machines which have too many registers for their own good)
diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index a48d7f1..67918c2 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -1,8 +1,43 @@
#ifndef __LINUX_UACCESS_H__
#define __LINUX_UACCESS_H__
+#include <linux/preempt.h>
#include <asm/uaccess.h>
+/*
+ * These routines enable/disable the pagefault handler in that
+ * it will not take any locks and go straight to the fixup table.
+ *
+ * They have great resemblance to the preempt_disable/enable calls
+ * and in fact they are identical; this is because currently there is
+ * no other way to make the pagefault handlers do this. So we do
+ * disable preemption but we don't necessarily care about that.
+ */
+static inline void pagefault_disable(void)
+{
+ inc_preempt_count();
+ /*
+ * make sure to have issued the store before a pagefault
+ * can hit.
+ */
+ barrier();
+}
+
+static inline void pagefault_enable(void)
+{
+ /*
+ * make sure to issue those last loads/stores before enabling
+ * the pagefault handler again.
+ */
+ barrier();
+ dec_preempt_count();
+ /*
+ * make sure we do..
+ */
+ barrier();
+ preempt_check_resched();
+}
+
#ifndef ARCH_HAS_NOCACHE_UACCESS
static inline unsigned long __copy_from_user_inatomic_nocache(void *to,
This change causes lots of compile errors of the following form on m68k:
| linux-2.6.20-rc4/include/linux/uaccess.h: In function `pagefault_disable':
| linux-2.6.20-rc4/include/linux/uaccess.h:18: error: dereferencing pointer to incomplete type
| linux-2.6.20-rc4/include/linux/uaccess.h: In function `pagefault_enable':
| linux-2.6.20-rc4/include/linux/uaccess.h:33: error: dereferencing pointer to incomplete type
-> inc_preempt_count
-> add_preempt_count
-> preempt_count
-> current_thread_info
-> task_thread_info
which needs the definition of struct task_struct.
The patch below fixes it by including <linux/sched.h> in
include/linux/uaccess.h. But perhaps this is the right time to move
struct task_struct to its own include instead?
Signed-off-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index 67918c2..ae73f32 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -2,6 +2,7 @@
#define __LINUX_UACCESS_H__
#include <linux/preempt.h>
+#include <linux/sched.h>
#include <asm/uaccess.h>
/*
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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