linux-kernel - [PATCH 2/2] Introduce __cond_lock

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Date:   Tue, 19 Dec 2017 08:58:23 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     linux-kernel@...r.kernel.org,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>, linux-mm@...ck.org,
        Josh Triplett <josh@...htriplett.org>
Cc:     Matthew Wilcox <mawilcox@...rosoft.com>
Subject: [PATCH 2/2] Introduce __cond_lock_err

From: Matthew Wilcox <mawilcox@...rosoft.com>

The __cond_lock macro expects the function to return 'true' if the lock
was acquired and 'false' if it wasn't.  We have another common calling
convention in the kernel, which is returning 0 on success and an errno
on failure.  It's hard to use the existing __cond_lock macro for those
kinds of functions, so introduce __cond_lock_err() and convert the
two existing users.

Signed-off-by: Matthew Wilcox <mawilcox@...rosoft.com>
---
 include/linux/compiler_types.h | 2 ++
 include/linux/mm.h             | 9 ++-------
 mm/memory.c                    | 9 ++-------
 3 files changed, 6 insertions(+), 14 deletions(-)

diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index 6b79a9bba9a7..ff3c41c78efa 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -16,6 +16,7 @@
 # define __acquire(x)	__context__(x,1)
 # define __release(x)	__context__(x,-1)
 # define __cond_lock(x,c)	((c) ? ({ __acquire(x); 1; }) : 0)
+# define __cond_lock_err(x,c)	((c) ? 1 : ({ __acquire(x); 0; }))
 # define __percpu	__attribute__((noderef, address_space(3)))
 # define __rcu		__attribute__((noderef, address_space(4)))
 # define __private	__attribute__((noderef))
@@ -42,6 +43,7 @@ extern void __chk_io_ptr(const volatile void __iomem *);
 # define __acquire(x) (void)0
 # define __release(x) (void)0
 # define __cond_lock(x,c) (c)
+# define __cond_lock_err(x,c) (c)
 # define __percpu
 # define __rcu
 # define __private
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 94a9d2149bd6..2ccdc980296b 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1328,13 +1328,8 @@ static inline int follow_pte_pmd(struct mm_struct *mm, unsigned long address,
 			     unsigned long *start, unsigned long *end,
 			     pte_t **ptepp, pmd_t **pmdpp, spinlock_t **ptlp)
 {
-	int res;
-
-	/* (void) is needed to make gcc happy */
-	(void) __cond_lock(*ptlp,
-			   !(res = __follow_pte_pmd(mm, address, start, end,
-						    ptepp, pmdpp, ptlp)));
-	return res;
+	return __cond_lock_err(*ptlp, __follow_pte_pmd(mm, address, start, end,
+						    ptepp, pmdpp, ptlp));
 }
 
 static inline void unmap_shared_mapping_range(struct address_space *mapping,
diff --git a/mm/memory.c b/mm/memory.c
index cb433662af21..92d58309cf45 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4269,13 +4269,8 @@ int __follow_pte_pmd(struct mm_struct *mm, unsigned long address,
 static inline int follow_pte(struct mm_struct *mm, unsigned long address,
 			     pte_t **ptepp, spinlock_t **ptlp)
 {
-	int res;
-
-	/* (void) is needed to make gcc happy */
-	(void) __cond_lock(*ptlp,
-			   !(res = __follow_pte_pmd(mm, address, NULL, NULL,
-						    ptepp, NULL, ptlp)));
-	return res;
+	return __cond_lock_err(*ptlp, __follow_pte_pmd(mm, address, NULL, NULL,
+						    ptepp, NULL, ptlp));
 }
 
 /**
-- 
2.15.1