x86/gup: Replace ACCESS_ONCE with READ_ONCE

borntraeger · borntraeger · commit 14cf3d977b80 · 2014-12-18T09:54:38.000+01:00
ACCESS_ONCE does not work reliably on non-scalar types. For example gcc 4.6 and 4.7 might remove the volatile tag for such accesses during the SRA (scalar replacement of aggregates) step (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145) Change the gup code to replace ACCESS_ONCE with READ_ONCE. Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c
@@ -15,7 +15,7 @@
 static inline pte_t gup_get_pte(pte_t *ptep)
 {
 #ifndef CONFIG_X86_PAE
-	return ACCESS_ONCE(*ptep);
+	return READ_ONCE(*ptep);
 #else
 	/*
 	 * With get_user_pages_fast, we walk down the pagetables without taking

Original file line number	Diff line number	Diff line change
`@@ -15,7 +15,7 @@`
`15`	`15`	`static inline pte_t gup_get_pte(pte_t *ptep)`
`16`	`16`	`{`
`17`	`17`	`#ifndef CONFIG_X86_PAE`
`18`		`- return ACCESS_ONCE(*ptep);`
	`18`	`+ return READ_ONCE(*ptep);`
`19`	`19`	`#else`
`20`	`20`	`/*`
`21`	`21`	`* With get_user_pages_fast, we walk down the pagetables without taking`