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Message-ID: <20061227212555.GA14947@elte.hu>
Date: Wed, 27 Dec 2006 22:25:55 +0100
From: Ingo Molnar <mingo@...e.hu>
To: Daniel Walker <dwalker@...sta.com>
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH -rt] update kmap_atomic on !HIGHMEM
* Daniel Walker <dwalker@...sta.com> wrote:
> I got some scheduling while atomic on x86-64 , and since x86-64
> doesn't seem to have HIGHMEM there's no workaround for kmap_atomic() .
>
> This patch adds the same as i386 HIGHMEM for !HIGHMEM.
the problem is that this does not disable pagefaulting while
kmap-atomic. Could you try the patch below, does it solve the assert?
Ingo
------------------------->
Subject: [patch] clean up the page fault disabling logic
From: Ingo Molnar <mingo@...e.hu>
decouple the pagefault-disabled logic from the preempt count.
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
arch/arm/mm/fault.c | 2 +-
arch/i386/mm/fault.c | 2 +-
arch/mips/mm/fault.c | 2 +-
arch/powerpc/mm/fault.c | 2 +-
arch/x86_64/mm/fault.c | 2 +-
include/linux/sched.h | 1 +
include/linux/uaccess.h | 33 +++------------------------------
kernel/fork.c | 1 +
mm/memory.c | 20 ++++++++++++++++++++
9 files changed, 30 insertions(+), 35 deletions(-)
Index: linux/arch/arm/mm/fault.c
===================================================================
--- linux.orig/arch/arm/mm/fault.c
+++ linux/arch/arm/mm/fault.c
@@ -230,7 +230,7 @@ do_page_fault(unsigned long addr, unsign
* If we're in an interrupt or have no user
* context, we must not take the fault..
*/
- if (in_atomic() || !mm)
+ if (in_atomic() || !mm || current->pagefault_disabled)
goto no_context;
/*
Index: linux/arch/i386/mm/fault.c
===================================================================
--- linux.orig/arch/i386/mm/fault.c
+++ linux/arch/i386/mm/fault.c
@@ -382,7 +382,7 @@ fastcall notrace void __kprobes do_page_
* If we're in an interrupt, have no user context or are running in an
* atomic region then we must not take the fault..
*/
- if (in_atomic() || !mm)
+ if (in_atomic() || !mm || current->pagefault_disabled)
goto bad_area_nosemaphore;
/* When running in the kernel we expect faults to occur only to
Index: linux/arch/mips/mm/fault.c
===================================================================
--- linux.orig/arch/mips/mm/fault.c
+++ linux/arch/mips/mm/fault.c
@@ -69,7 +69,7 @@ asmlinkage void do_page_fault(struct pt_
* If we're in an interrupt or have no user
* context, we must not take the fault..
*/
- if (in_atomic() || !mm)
+ if (in_atomic() || !mm || current->pagefault_disabled)
goto bad_area_nosemaphore;
down_read(&mm->mmap_sem);
Index: linux/arch/powerpc/mm/fault.c
===================================================================
--- linux.orig/arch/powerpc/mm/fault.c
+++ linux/arch/powerpc/mm/fault.c
@@ -196,7 +196,7 @@ int __kprobes notrace do_page_fault(stru
}
#endif /* !(CONFIG_4xx || CONFIG_BOOKE)*/
- if (in_atomic() || mm == NULL) {
+ if (in_atomic() || mm == NULL || current->pagefault_disabled) {
if (!user_mode(regs))
return SIGSEGV;
/* in_atomic() in user mode is really bad,
Index: linux/arch/x86_64/mm/fault.c
===================================================================
--- linux.orig/arch/x86_64/mm/fault.c
+++ linux/arch/x86_64/mm/fault.c
@@ -405,7 +405,7 @@ asmlinkage void __kprobes do_page_fault(
* If we're in an interrupt or have no user
* context, we must not take the fault..
*/
- if (unlikely(in_atomic() || !mm))
+ if (unlikely(in_atomic() || !mm || current->pagefault_disabled))
goto bad_area_nosemaphore;
again:
Index: linux/include/linux/sched.h
===================================================================
--- linux.orig/include/linux/sched.h
+++ linux/include/linux/sched.h
@@ -1147,6 +1147,7 @@ struct task_struct {
/* mutex deadlock detection */
struct mutex_waiter *blocked_on;
#endif
+ int pagefault_disabled;
#ifdef CONFIG_TRACE_IRQFLAGS
unsigned int irq_events;
int hardirqs_enabled;
Index: linux/include/linux/uaccess.h
===================================================================
--- linux.orig/include/linux/uaccess.h
+++ linux/include/linux/uaccess.h
@@ -6,37 +6,10 @@
/*
* 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.
+ * it will not take any MM locks and go straight to the fixup table.
*/
-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();
-}
+extern void pagefault_disable(void);
+extern void pagefault_enable(void);
#ifndef ARCH_HAS_NOCACHE_UACCESS
Index: linux/kernel/fork.c
===================================================================
--- linux.orig/kernel/fork.c
+++ linux/kernel/fork.c
@@ -1128,6 +1128,7 @@ static struct task_struct *copy_process(
p->hardirq_context = 0;
p->softirq_context = 0;
#endif
+ p->pagefault_disabled = 0;
#ifdef CONFIG_LOCKDEP
p->lockdep_depth = 0; /* no locks held yet */
p->curr_chain_key = 0;
Index: linux/mm/memory.c
===================================================================
--- linux.orig/mm/memory.c
+++ linux/mm/memory.c
@@ -2481,6 +2481,26 @@ unlock:
return VM_FAULT_MINOR;
}
+void pagefault_disable(void)
+{
+ current->pagefault_disabled++;
+ /*
+ * make sure to have issued the store before a pagefault
+ * can hit.
+ */
+ barrier();
+}
+
+void pagefault_enable(void)
+{
+ /*
+ * make sure to issue those last loads/stores before enabling
+ * the pagefault handler again.
+ */
+ barrier();
+ current->pagefault_disabled--;
+}
+
/*
* By the time we get here, we already hold the mm semaphore
*/
-
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