linux-kernel - [PATCH] enable interrupts in user path of page fault.

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Date:	Wed, 06 Jun 2007 23:34:04 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Linus Torvalds <torvalds@...l.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@...l.org>, Andi Kleen <ak@...e.de>
Subject: [PATCH] enable interrupts in user path of page fault.

This is a minor fix, but what is currently there is essentially wrong.
In do_page_fault, if the faulting address from user code happens to be
in kernel address space (int *p = (int*)-1; p = 0xbed;)  then the
do_page_fault handler will jump over the local_irq_enable with the

  goto bad_area_nosemaphore;

But the first line there sees this is user code and goes through the
process of sending a signal to send SIGSEGV to the user task. This whole
time interrupts are disabled and the task can not be preempted by a
higher priority task.

This patch always enables interrupts in the user path of the
bad_area_nosemaphore.

Signed-off-by: Steven Rostedt <rostedt@...dmis.org>

diff --git a/arch/i386/mm/fault.c b/arch/i386/mm/fault.c
index 29d7d61..1ecb3e4 100644
--- a/arch/i386/mm/fault.c
+++ b/arch/i386/mm/fault.c
@@ -458,6 +458,11 @@ bad_area:
 bad_area_nosemaphore:
 	/* User mode accesses just cause a SIGSEGV */
 	if (error_code & 4) {
+		/*
+		 * It's possible to have interrupts off here.
+		 */
+		local_irq_enable();
+
 		/* 
 		 * Valid to do another page fault here because this one came 
 		 * from user space.
diff --git a/arch/x86_64/mm/fault.c b/arch/x86_64/mm/fault.c
index bfb62a1..635e58d 100644
--- a/arch/x86_64/mm/fault.c
+++ b/arch/x86_64/mm/fault.c
@@ -476,6 +476,12 @@ bad_area:
 bad_area_nosemaphore:
 	/* User mode accesses just cause a SIGSEGV */
 	if (error_code & PF_USER) {
+
+		/*
+		 * It's possible to have interrupts off here.
+		 */
+		local_irq_enable();
+
 		if (is_prefetch(regs, address, error_code))
 			return;
 


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