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   1 From foo@baz Sun Jun 17 12:07:34 CEST 2018
   2 From: Waiman Long <longman@redhat.com>
   3 Date: Tue, 15 May 2018 17:49:51 -0400
   4 Subject: locking/percpu-rwsem: Annotate rwsem ownership transfer by setting RWSEM_OWNER_UNKNOWN
   5
   6 From: Waiman Long <longman@redhat.com>
   7
   8 [ Upstream commit 5a817641f68a6399a5fac8b7d2da67a73698ffed ]
   9
  10 The filesystem freezing code needs to transfer ownership of a rwsem
  11 embedded in a percpu-rwsem from the task that does the freezing to
  12 another one that does the thawing by calling percpu_rwsem_release()
  13 after freezing and percpu_rwsem_acquire() before thawing.
  14
  15 However, the new rwsem debug code runs afoul with this scheme by warning
  16 that the task that releases the rwsem isn't the one that acquires it,
  17 as reported by Amir Goldstein:
  18
  19   DEBUG_LOCKS_WARN_ON(sem->owner != get_current())
  20   WARNING: CPU: 1 PID: 1401 at /home/amir/build/src/linux/kernel/locking/rwsem.c:133 up_write+0x59/0x79
  21
  22   Call Trace:
  23    percpu_up_write+0x1f/0x28
  24    thaw_super_locked+0xdf/0x120
  25    do_vfs_ioctl+0x270/0x5f1
  26    ksys_ioctl+0x52/0x71
  27    __x64_sys_ioctl+0x16/0x19
  28    do_syscall_64+0x5d/0x167
  29    entry_SYSCALL_64_after_hwframe+0x49/0xbe
  30
  31 To work properly with the rwsem debug code, we need to annotate that the
  32 rwsem ownership is unknown during the tranfer period until a brave soul
  33 comes forward to acquire the ownership. During that period, optimistic
  34 spinning will be disabled.
  35
  36 Reported-by: Amir Goldstein <amir73il@gmail.com>
  37 Tested-by: Amir Goldstein <amir73il@gmail.com>
  38 Signed-off-by: Waiman Long <longman@redhat.com>
  39 Acked-by: Peter Zijlstra <peterz@infradead.org>
  40 Cc: Andrew Morton <akpm@linux-foundation.org>
  41 Cc: Davidlohr Bueso <dave@stgolabs.net>
  42 Cc: Jan Kara <jack@suse.cz>
  43 Cc: Linus Torvalds <torvalds@linux-foundation.org>
  44 Cc: Matthew Wilcox <willy@infradead.org>
  45 Cc: Oleg Nesterov <oleg@redhat.com>
  46 Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
  47 Cc: Theodore Y. Ts'o <tytso@mit.edu>
  48 Cc: Thomas Gleixner <tglx@linutronix.de>
  49 Cc: Will Deacon <will.deacon@arm.com>
  50 Cc: linux-fsdevel@vger.kernel.org
  51 Link: http://lkml.kernel.org/r/1526420991-21213-3-git-send-email-longman@redhat.com
  52 Signed-off-by: Ingo Molnar <mingo@kernel.org>
  53 Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
  54 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  55 ---
  56  include/linux/percpu-rwsem.h |    6 +++++-
  57  include/linux/rwsem.h        |    6 ++++++
  58  kernel/locking/rwsem-xadd.c  |    2 ++
  59  3 files changed, 13 insertions(+), 1 deletion(-)
  60
  61 --- a/include/linux/percpu-rwsem.h
  62 +++ b/include/linux/percpu-rwsem.h
  63 @@ -133,7 +133,7 @@ static inline void percpu_rwsem_release(
  64         lock_release(&sem->rw_sem.dep_map, 1, ip);
  65  #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
  66         if (!read)
  67 -               sem->rw_sem.owner = NULL;
  68 +               sem->rw_sem.owner = RWSEM_OWNER_UNKNOWN;
  69  #endif
  70  }
  71
  72 @@ -141,6 +141,10 @@ static inline void percpu_rwsem_acquire(
  73                                         bool read, unsigned long ip)
  74  {
  75         lock_acquire(&sem->rw_sem.dep_map, 0, 1, read, 1, NULL, ip);
  76 +#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
  77 +       if (!read)
  78 +               sem->rw_sem.owner = current;
  79 +#endif
  80  }
  81
  82  #endif
  83 --- a/include/linux/rwsem.h
  84 +++ b/include/linux/rwsem.h
  85 @@ -44,6 +44,12 @@ struct rw_semaphore {
  86  #endif
  87  };
  88
  89 +/*
  90 + * Setting bit 0 of the owner field with other non-zero bits will indicate
  91 + * that the rwsem is writer-owned with an unknown owner.
  92 + */
  93 +#define RWSEM_OWNER_UNKNOWN    ((struct task_struct *)-1L)
  94 +
  95  extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
  96  extern struct rw_semaphore *rwsem_down_read_failed_killable(struct rw_semaphore *sem);
  97  extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
  98 --- a/kernel/locking/rwsem-xadd.c
  99 +++ b/kernel/locking/rwsem-xadd.c
 100 @@ -352,6 +352,8 @@ static inline bool rwsem_can_spin_on_own
 101         struct task_struct *owner;
 102         bool ret = true;
 103
 104 +       BUILD_BUG_ON(!rwsem_has_anonymous_owner(RWSEM_OWNER_UNKNOWN));
 105 +
 106         if (need_resched())
 107                 return false;
 108