[RFC][PATCH 5/5] x86_64: lockless fault handler

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

[-- Attachment #1: fault-x86_64.patch --]
[-- Type: text/plain, Size: 2014 bytes --]

avoid taking the rw-sem

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
 arch/x86_64/mm/fault.c |   17 +++++------------
 1 file changed, 5 insertions(+), 12 deletions(-)

Index: linux-2.6/arch/x86_64/mm/fault.c
===================================================================
--- linux-2.6.orig/arch/x86_64/mm/fault.c
+++ linux-2.6/arch/x86_64/mm/fault.c
@@ -344,7 +344,6 @@ asmlinkage void __kprobes do_page_fault(
 
 	tsk = current;
 	mm = tsk->mm;
-	prefetchw(&mm->mmap_sem);
 
 	/* get the address */
 	__asm__("movq %%cr2,%0":"=r" (address));
@@ -423,14 +422,8 @@ asmlinkage void __kprobes do_page_fault(
 	 * source.  If this is invalid we can skip the address space check,
 	 * thus avoiding the deadlock.
 	 */
-	if (!down_read_trylock(&mm->mmap_sem)) {
-		if ((error_code & PF_USER) == 0 &&
-		    !search_exception_tables(regs->rip))
-			goto bad_area_nosemaphore;
-		down_read(&mm->mmap_sem);
-	}
 
-	vma = find_vma(mm, address);
+	vma = find_get_vma(mm, address);
 	if (!vma)
 		goto bad_area;
 	if (likely(vma->vm_start <= address))
@@ -486,7 +479,7 @@ good_area:
 		goto out_of_memory;
 	}
 
-	up_read(&mm->mmap_sem);
+	put_vma(vma);
 	return;
 
 /*
@@ -494,7 +487,7 @@ good_area:
  * Fix it, but check if it's kernel or user first..
  */
 bad_area:
-	up_read(&mm->mmap_sem);
+	put_vma(vma);
 
 bad_area_nosemaphore:
 	/* User mode accesses just cause a SIGSEGV */
@@ -579,7 +572,7 @@ no_context:
  * us unable to handle the page fault gracefully.
  */
 out_of_memory:
-	up_read(&mm->mmap_sem);
+	put_vma(vma);
 	if (is_init(current)) {
 		yield();
 		goto again;
@@ -590,7 +583,7 @@ out_of_memory:
 	goto no_context;
 
 do_sigbus:
-	up_read(&mm->mmap_sem);
+	put_vma(vma);
 
 	/* Kernel mode? Handle exceptions or die */
 	if (!(error_code & PF_USER))

-- 

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