releases/3.11.6/ipc-sem.c-update-sem_otime-for-all-operations.patch

   1 From 0e8c665699e953fa58dc1b0b0d09e5dce7343cc7 Mon Sep 17 00:00:00 2001
   2 From: Manfred Spraul <manfred@colorfullife.com>
   3 Date: Mon, 30 Sep 2013 13:45:25 -0700
   4 Subject: ipc/sem.c: update sem_otime for all operations
   5
   6 From: Manfred Spraul <manfred@colorfullife.com>
   7
   8 commit 0e8c665699e953fa58dc1b0b0d09e5dce7343cc7 upstream.
   9
  10 In commit 0a2b9d4c7967 ("ipc/sem.c: move wake_up_process out of the
  11 spinlock section"), the update of semaphore's sem_otime(last semop time)
  12 was moved to one central position (do_smart_update).
  13
  14 But since do_smart_update() is only called for operations that modify
  15 the array, this means that wait-for-zero semops do not update sem_otime
  16 anymore.
  17
  18 The fix is simple:
  19 Non-alter operations must update sem_otime.
  20
  21 [akpm@linux-foundation.org: coding-style fixes]
  22 Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
  23 Reported-by: Jia He <jiakernel@gmail.com>
  24 Tested-by: Jia He <jiakernel@gmail.com>
  25 Cc: Davidlohr Bueso <davidlohr.bueso@hp.com>
  26 Cc: Mike Galbraith <efault@gmx.de>
  27 Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
  28 Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
  29 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  30
  31 ---
  32  ipc/sem.c |   42 +++++++++++++++++++++++++++++-------------
  33  1 file changed, 29 insertions(+), 13 deletions(-)
  34
  35 --- a/ipc/sem.c
  36 +++ b/ipc/sem.c
  37 @@ -918,6 +918,24 @@ again:
  38  }
  39
  40  /**
  41 + * set_semotime(sma, sops) - set sem_otime
  42 + * @sma: semaphore array
  43 + * @sops: operations that modified the array, may be NULL
  44 + *
  45 + * sem_otime is replicated to avoid cache line trashing.
  46 + * This function sets one instance to the current time.
  47 + */
  48 +static void set_semotime(struct sem_array *sma, struct sembuf *sops)
  49 +{
  50 +       if (sops == NULL) {
  51 +               sma->sem_base[0].sem_otime = get_seconds();
  52 +       } else {
  53 +               sma->sem_base[sops[0].sem_num].sem_otime =
  54 +                                                       get_seconds();
  55 +       }
  56 +}
  57 +
  58 +/**
  59   * do_smart_update(sma, sops, nsops, otime, pt) - optimized update_queue
  60   * @sma: semaphore array
  61   * @sops: operations that were performed
  62 @@ -967,17 +985,10 @@ static void do_smart_update(struct sem_a
  63                         }
  64                 }
  65         }
  66 -       if (otime) {
  67 -               if (sops == NULL) {
  68 -                       sma->sem_base[0].sem_otime = get_seconds();
  69 -               } else {
  70 -                       sma->sem_base[sops[0].sem_num].sem_otime =
  71 -                                                               get_seconds();
  72 -               }
  73 -       }
  74 +       if (otime)
  75 +               set_semotime(sma, sops);
  76  }
  77
  78 -
  79  /* The following counts are associated to each semaphore:
  80   *   semncnt        number of tasks waiting on semval being nonzero
  81   *   semzcnt        number of tasks waiting on semval being zero
  82 @@ -1839,12 +1850,17 @@ SYSCALL_DEFINE4(semtimedop, int, semid,
  83
  84         error = perform_atomic_semop(sma, sops, nsops, un,
  85                                         task_tgid_vnr(current));
  86 -       if (error <= 0) {
  87 -               if (alter && error == 0)
  88 +       if (error == 0) {
  89 +               /* If the operation was successful, then do
  90 +                * the required updates.
  91 +                */
  92 +               if (alter)
  93                         do_smart_update(sma, sops, nsops, 1, &tasks);
  94 -
  95 -               goto out_unlock_free;
  96 +               else
  97 +                       set_semotime(sma, sops);
  98         }
  99 +       if (error <= 0)
 100 +               goto out_unlock_free;
 101
 102         /* We need to sleep on this operation, so we put the current
 103          * task into the pending queue and go to sleep.