Linux 4.8 compat: rw_semaphore atomic_long_t count

For non-rwsem-spinlocks the "count" member was changed from a "long" to "atomic_long_t" type. A configure check has been added to detect this change along with new versions of the _rwsem_tryupgrade() function and RWSEM_COUNT() macro. See torvalds/linux@8ee62b18 for complete details. Signed-off-by: Tim Chase <[email protected]> Signed-off-by: Chunwei Chen <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]> Closes openzfs#563
rtvd · Jul 29, 2016 · b7c7008 · b7c7008
1 parent d2f97b2
commit b7c7008
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Showing 3 changed files with 41 additions and 3 deletions.
diff --git a/config/spl-build.m4 b/config/spl-build.m4
@@ -40,6 +40,7 @@ AC_DEFUN([SPL_AC_CONFIG_KERNEL], [
  SPL_AC_SHRINK_CONTROL_STRUCT
  SPL_AC_RWSEM_SPINLOCK_IS_RAW
  SPL_AC_RWSEM_ACTIVITY
+ SPL_AC_RWSEM_ATOMIC_LONG_COUNT
  SPL_AC_SCHED_RT_HEADER
  SPL_AC_2ARGS_VFS_GETATTR
  SPL_AC_USLEEP_RANGE
@@ -1341,6 +1342,31 @@ AC_DEFUN([SPL_AC_RWSEM_ACTIVITY], [
  EXTRA_KCFLAGS="$tmp_flags"
 ])
 
+dnl #
+dnl # 4.8 API Change
+dnl #
+dnl # rwsem "->count" changed to atomic_long_t type
+dnl #
+AC_DEFUN([SPL_AC_RWSEM_ATOMIC_LONG_COUNT], [
+ AC_MSG_CHECKING(
+ [whether struct rw_semaphore has atomic_long_t member count])
+ tmp_flags="$EXTRA_KCFLAGS"
+ EXTRA_KCFLAGS="-Werror"
+ SPL_LINUX_TRY_COMPILE([
+ #include <linux/rwsem.h>
+ ],[
+ DECLARE_RWSEM(dummy_semaphore);
+ (void) atomic_long_read(&dummy_semaphore.count);
+ ],[
+ AC_MSG_RESULT(yes)
+ AC_DEFINE(HAVE_RWSEM_ATOMIC_LONG_COUNT, 1,
+ [struct rw_semaphore has atomic_long_t member count])
+ ],[
+ AC_MSG_RESULT(no)
+ ])
+ EXTRA_KCFLAGS="$tmp_flags"
+])
+
 dnl #
 dnl # 3.9 API change,
 dnl # Moved things from linux/sched.h to linux/sched/rt.h

diff --git a/include/linux/rwsem_compat.h b/include/linux/rwsem_compat.h
@@ -35,9 +35,12 @@
 #define SPL_RWSEM_SINGLE_WRITER_VALUE (RWSEM_ACTIVE_WRITE_BIAS)
 #endif
 
-/* Linux 3.16 change activity to count for rwsem-spinlock */
-#ifdef HAVE_RWSEM_ACTIVITY
+/* Linux 3.16 changed activity to count for rwsem-spinlock */
+#if defined(HAVE_RWSEM_ACTIVITY)
 #define RWSEM_COUNT(sem) sem->activity
+/* Linux 4.8 changed count to an atomic_long_t for !rwsem-spinlock */
+#elif defined(HAVE_RWSEM_ATOMIC_LONG_COUNT)
+#define RWSEM_COUNT(sem) atomic_long_read(&(sem)->count)
 #else
 #define RWSEM_COUNT(sem) sem->count
 #endif

diff --git a/module/spl/spl-rwlock.c b/module/spl/spl-rwlock.c
@@ -32,7 +32,7 @@
 
 #define DEBUG_SUBSYSTEM S_RWLOCK
 
-#ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
+#if defined(CONFIG_RWSEM_GENERIC_SPINLOCK)
 static int
 __rwsem_tryupgrade(struct rw_semaphore *rwsem)
 {
@@ -47,6 +47,15 @@ __rwsem_tryupgrade(struct rw_semaphore *rwsem)
  spl_rwsem_unlock_irqrestore(&rwsem->wait_lock, flags);
  return (ret);
 }
+#elif defined(HAVE_RWSEM_ATOMIC_LONG_COUNT)
+static int
+__rwsem_tryupgrade(struct rw_semaphore *rwsem)
+{
+ long val;
+ val = atomic_long_cmpxchg(&rwsem->count, SPL_RWSEM_SINGLE_READER_VALUE,
+ SPL_RWSEM_SINGLE_WRITER_VALUE);
+ return (val == SPL_RWSEM_SINGLE_READER_VALUE);
+}
 #else
 static int
 __rwsem_tryupgrade(struct rw_semaphore *rwsem)