mm/gup: Overload get_user_pages() functions

The concept here was a suggestion from Ingo.  The implementation
horrors are all mine.

This allows get_user_pages(), get_user_pages_unlocked(), and
get_user_pages_locked() to be called with or without the
leading tsk/mm arguments.  We will give a compile-time warning
about the old style being __deprecated and we will also
WARN_ON() if the non-remote version is used for a remote-style
access.

Doing this, folks will get nice warnings and will not break the
build.  This should be nice for -next and will hopefully let
developers fix up their own code instead of maintainers needing
to do it at merge time.

The way we do this is hideous.  It uses the __VA_ARGS__ macro
functionality to call different functions based on the number
of arguments passed to the macro.

There's an additional hack to ensure that our EXPORT_SYMBOL()
of the deprecated symbols doesn't trigger a warning.

We should be able to remove this mess as soon as -rc1 hits in
the release after this is merged.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Alexander Kuleshov <kuleshovmail@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Hansen <dave@sr71.net>
Cc: Dominik Dingel <dingel@linux.vnet.ibm.com>
Cc: Geliang Tang <geliangtang@163.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Leon Romanovsky <leon@leon.nu>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Mateusz Guzik <mguzik@redhat.com>
Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Xie XiuQi <xiexiuqi@huawei.com>
Cc: linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/20160212210155.73222EE1@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 64 insertions, 10 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index faf3b709eead..4c7317828fda 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1229,24 +1229,78 @@ long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
 			    unsigned long start, unsigned long nr_pages,
 			    int write, int force, struct page **pages,
 			    struct vm_area_struct **vmas);
-long get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
-		    unsigned long start, unsigned long nr_pages,
-		    int write, int force, struct page **pages,
-		    struct vm_area_struct **vmas);
-long get_user_pages_locked(struct task_struct *tsk, struct mm_struct *mm,
-		    unsigned long start, unsigned long nr_pages,
-		    int write, int force, struct page **pages,
-		    int *locked);
+long get_user_pages6(unsigned long start, unsigned long nr_pages,
+			    int write, int force, struct page **pages,
+			    struct vm_area_struct **vmas);
+long get_user_pages_locked6(unsigned long start, unsigned long nr_pages,
+		    int write, int force, struct page **pages, int *locked);
 long __get_user_pages_unlocked(struct task_struct *tsk, struct mm_struct *mm,
 			       unsigned long start, unsigned long nr_pages,
 			       int write, int force, struct page **pages,
 			       unsigned int gup_flags);
-long get_user_pages_unlocked(struct task_struct *tsk, struct mm_struct *mm,
-		    unsigned long start, unsigned long nr_pages,
+long get_user_pages_unlocked5(unsigned long start, unsigned long nr_pages,
 		    int write, int force, struct page **pages);
 int get_user_pages_fast(unsigned long start, int nr_pages, int write,
 			struct page **pages);
 
+/* suppress warnings from use in EXPORT_SYMBOL() */
+#ifndef __DISABLE_GUP_DEPRECATED
+#define __gup_deprecated __deprecated
+#else
+#define __gup_deprecated
+#endif
+/*
+ * These macros provide backward-compatibility with the old
+ * get_user_pages() variants which took tsk/mm.  These
+ * functions/macros provide both compile-time __deprecated so we
+ * can catch old-style use and not break the build.  The actual
+ * functions also have WARN_ON()s to let us know at runtime if
+ * the get_user_pages() should have been the "remote" variant.
+ *
+ * These are hideous, but temporary.
+ *
+ * If you run into one of these __deprecated warnings, look
+ * at how you are calling get_user_pages().  If you are calling
+ * it with current/current->mm as the first two arguments,
+ * simply remove those arguments.  The behavior will be the same
+ * as it is now.  If you are calling it on another task, use
+ * get_user_pages_remote() instead.
+ *
+ * Any questions?  Ask Dave Hansen <dave@sr71.net>
+ */
+long
+__gup_deprecated
+get_user_pages8(struct task_struct *tsk, struct mm_struct *mm,
+		unsigned long start, unsigned long nr_pages,
+		int write, int force, struct page **pages,
+		struct vm_area_struct **vmas);
+#define GUP_MACRO(_1, _2, _3, _4, _5, _6, _7, _8, get_user_pages, ...)	\
+	get_user_pages
+#define get_user_pages(...) GUP_MACRO(__VA_ARGS__,	\
+		get_user_pages8, x,			\
+		get_user_pages6, x, x, x, x, x)(__VA_ARGS__)
+
+__gup_deprecated
+long get_user_pages_locked8(struct task_struct *tsk, struct mm_struct *mm,
+		unsigned long start, unsigned long nr_pages,
+		int write, int force, struct page **pages,
+		int *locked);
+#define GUPL_MACRO(_1, _2, _3, _4, _5, _6, _7, _8, get_user_pages_locked, ...)	\
+	get_user_pages_locked
+#define get_user_pages_locked(...) GUPL_MACRO(__VA_ARGS__,	\
+		get_user_pages_locked8,	x,			\
+		get_user_pages_locked6, x, x, x, x)(__VA_ARGS__)
+
+__gup_deprecated
+long get_user_pages_unlocked7(struct task_struct *tsk, struct mm_struct *mm,
+		unsigned long start, unsigned long nr_pages,
+		int write, int force, struct page **pages);
+#define GUPU_MACRO(_1, _2, _3, _4, _5, _6, _7, get_user_pages_unlocked, ...)	\
+	get_user_pages_unlocked
+#define get_user_pages_unlocked(...) GUPU_MACRO(__VA_ARGS__,	\
+		get_user_pages_unlocked7, x,			\
+		get_user_pages_unlocked5, x, x, x, x)(__VA_ARGS__)
+
 /* Container for pinned pfns / pages */
 struct frame_vector {
 	unsigned int nr_allocated;	/* Number of frames we have space for */