Remove misguided HAVE_MUTEX_OWNER check, take 2

It is just plain unsafe to peek inside in-kernel
mutex structure and make assumptions about what kernel
does with those internal fields like owner.

Kernel is all too happy to stop doing the expected things
like tracing lock owner once you load a tainted module
like spl/zfs that is not GPL.

As such you will get instant assertion failures like this:

  VERIFY3(((*(volatile typeof((&((&zo->zo_lock)->m_mutex))->owner) *)&
      ((&((&zo->zo_lock)->m_mutex))->owner))) ==
     ((void *)0)) failed (ffff88030be28500 == (null))
  PANIC at zfs_onexit.c:104:zfs_onexit_destroy()
  Showing stack for process 3626
  CPU: 0 PID: 3626 Comm: mkfs.lustre Tainted: P OE ------------ 3.10.0-debug #1
  Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
  Call Trace:
  dump_stack+0x19/0x1b
  spl_dumpstack+0x44/0x50 [spl]
  spl_panic+0xbf/0xf0 [spl]
  zfs_onexit_destroy+0x17c/0x280 [zfs]
  zfsdev_release+0x48/0xd0 [zfs]

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Chunwei Chen <david.chen@osnexus.com>
Reviewed-by: Gvozden Neskovic <neskovic@gmail.com>
Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Closes #639
Closes #632

diff --git a/config/spl-build.m4 b/config/spl-build.m4
index 630d67c2d5daad0fa5c09e6ea82c82e026874f90..b2a50bf164b9908235587c6e00e786c5dc06583d 100644 (file)
--- a/config/spl-build.m4
+++ b/config/spl-build.m4
@@ -49,7 +49,6 @@ AC_DEFUN([SPL_AC_CONFIG_KERNEL], [
        SPL_AC_USLEEP_RANGE
        SPL_AC_KMEM_CACHE_ALLOCFLAGS
        SPL_AC_WAIT_ON_BIT
-       SPL_AC_MUTEX_OWNER
        SPL_AC_INODE_LOCK
        SPL_AC_GROUP_INFO_GID
        SPL_AC_KMEM_CACHE_CREATE_USERCOPY
@@ -1562,35 +1561,6 @@ AC_DEFUN([SPL_AC_WAIT_ON_BIT], [
        ])
 ])
 
-dnl #
-dnl # Check whether mutex has owner with task_struct type.
-dnl #
-dnl # Note that before Linux 3.0, mutex owner is of type thread_info.
-dnl #
-dnl # Note that in Linux 3.18, the condition for owner is changed from
-dnl # defined(CONFIG_DEBUG_MUTEXES) || defined(CONFIG_SMP) to
-dnl # defined(CONFIG_DEBUG_MUTEXES) || defined(CONFIG_MUTEX_SPIN_ON_OWNER)
-dnl #
-AC_DEFUN([SPL_AC_MUTEX_OWNER], [
-       AC_MSG_CHECKING([whether mutex has owner])
-       tmp_flags="$EXTRA_KCFLAGS"
-       EXTRA_KCFLAGS="-Werror"
-       SPL_LINUX_TRY_COMPILE([
-               #include <linux/mutex.h>
-               #include <linux/spinlock.h>
-       ],[
-               DEFINE_MUTEX(m);
-               struct task_struct *t __attribute__ ((unused));
-               t = m.owner;
-       ],[
-               AC_MSG_RESULT(yes)
-               AC_DEFINE(HAVE_MUTEX_OWNER, 1, [yes])
-       ],[
-               AC_MSG_RESULT(no)
-       ])
-       EXTRA_KCFLAGS="$tmp_flags"
-])
-
 dnl #
 dnl # 4.7 API change
 dnl # i_mutex is changed to i_rwsem. Instead of directly using

diff --git a/include/sys/mutex.h b/include/sys/mutex.h
index 8a98a92138d4497f5e5f6a59bf51e513ac9ac6c2..8cbab7c477ebc590910e4c528fb7893ab12d3700 100644 (file)
--- a/include/sys/mutex.h
+++ b/include/sys/mutex.h
@@ -40,10 +40,7 @@ typedef enum {
 typedef struct {
        struct mutex            m_mutex;
        spinlock_t              m_lock; /* used for serializing mutex_exit */
-#ifndef HAVE_MUTEX_OWNER
-       /* only when kernel doesn't have owner */
        kthread_t               *m_owner;
-#endif
 #ifdef CONFIG_LOCKDEP
        kmutex_type_t           m_type;
 #endif /* CONFIG_LOCKDEP */
@@ -54,28 +51,16 @@ typedef struct {
 static inline void
 spl_mutex_set_owner(kmutex_t *mp)
 {
-       /*
-        * kernel will handle its owner, so we don't need to do anything if it
-        * is defined.
-        */
-#ifndef HAVE_MUTEX_OWNER
        mp->m_owner = current;
-#endif
 }
 
 static inline void
 spl_mutex_clear_owner(kmutex_t *mp)
 {
-#ifndef HAVE_MUTEX_OWNER
        mp->m_owner = NULL;
-#endif
 }
 
-#ifdef HAVE_MUTEX_OWNER
-#define        mutex_owner(mp)         (ACCESS_ONCE(MUTEX(mp)->owner))
-#else
 #define        mutex_owner(mp)         (ACCESS_ONCE((mp)->m_owner))
-#endif
 #define        mutex_owned(mp)         (mutex_owner(mp) == current)
 #define        MUTEX_HELD(mp)          mutex_owned(mp)
 #define        MUTEX_NOT_HELD(mp)      (!MUTEX_HELD(mp))