Linux 4.20 compat: Fix VERIFY(RW_READ_HELD(&hash->mh_contents))

[mirror_zfs.git] / include / spl / sys / rwlock.h

diff --git a/include/spl/sys/rwlock.h b/include/spl/sys/rwlock.h
index 0ac528e165fc204d8ab0bf528b1c7bd7e1319caf..a1c1fd469f9473f4817e2a1af291b6a6061b0089 100644 (file)
--- a/include/spl/sys/rwlock.h
+++ b/include/spl/sys/rwlock.h
@@ -148,16 +148,6 @@ spl_rw_lockdep_on_maybe(krwlock_t *rwp)                    \
 #define        spl_rw_lockdep_on_maybe(rwp)
 #endif /* CONFIG_LOCKDEP */
 
-static inline int
-RW_READ_HELD(krwlock_t *rwp)
-{
-       /*
-        * Linux 4.8 will set owner to 1 when read held instead of leave it
-        * NULL. So we check whether owner <= 1.
-        */
-       return (spl_rwsem_is_locked(SEM(rwp)) &&
-           (unsigned long)rw_owner(rwp) <= 1);
-}
 
 static inline int
 RW_WRITE_HELD(krwlock_t *rwp)
@@ -171,6 +161,51 @@ RW_LOCK_HELD(krwlock_t *rwp)
        return (spl_rwsem_is_locked(SEM(rwp)));
 }
 
+static inline int
+RW_READ_HELD(krwlock_t *rwp)
+{
+       if (!RW_LOCK_HELD(rwp))
+               return (0);
+
+       /*
+        * rw_semaphore cheat sheet:
+        *
+        * < 3.16:
+        * There's no rw_semaphore.owner, so use rwp.owner instead.
+        * If rwp.owner == NULL then it's a reader
+        *
+        * 3.16 - 4.7:
+        * rw_semaphore.owner added (https://lwn.net/Articles/596656/)
+        * and CONFIG_RWSEM_SPIN_ON_OWNER introduced.
+        * If rw_semaphore.owner == NULL then it's a reader
+        *
+        * 4.8 - 4.16.16:
+        * RWSEM_READER_OWNED added as an internal #define.
+        * (https://lore.kernel.org/patchwork/patch/678590/)
+        * If rw_semaphore.owner == 1 then it's a reader
+        *
+        * 4.16.17 - 4.19:
+        * RWSEM_OWNER_UNKNOWN introduced as ((struct task_struct *)-1L)
+        * (https://do-db2.lkml.org/lkml/2018/5/15/985)
+        * If rw_semaphore.owner == 1 then it's a reader.
+        *
+        * 4.20+:
+        * RWSEM_OWNER_UNKNOWN changed to ((struct task_struct *)-2L)
+        * (https://lkml.org/lkml/2018/9/6/986)
+        * If rw_semaphore.owner & 1 then it's a reader, and also the reader's
+        * task_struct may be embedded in rw_semaphore->owner.
+        */
+#if    defined(CONFIG_RWSEM_SPIN_ON_OWNER) && defined(RWSEM_OWNER_UNKNOWN)
+       if (RWSEM_OWNER_UNKNOWN == (struct task_struct *)-2L) {
+               /* 4.20+ kernels with CONFIG_RWSEM_SPIN_ON_OWNER */
+               return ((unsigned long) SEM(rwp)->owner & 1);
+       }
+#endif
+
+       /* < 4.20 kernel or !CONFIG_RWSEM_SPIN_ON_OWNER */
+       return (rw_owner(rwp) == NULL || (unsigned long) rw_owner(rwp) == 1);
+}
+
 /*
  * The following functions must be a #define and not static inline.
  * This ensures that the native linux semaphore functions (down/up)