1. 16 Jul, 2014 27 commits
  2. 15 Jul, 2014 12 commits
  3. 14 Jul, 2014 1 commit
    • Oleg Nesterov's avatar
      introduce for_each_thread() to replace the buggy while_each_thread() · e1790aea
      Oleg Nesterov authored
      commit 0c740d0a upstream.
      
      while_each_thread() and next_thread() should die, almost every lockless
      usage is wrong.
      
      1. Unless g == current, the lockless while_each_thread() is not safe.
      
         while_each_thread(g, t) can loop forever if g exits, next_thread()
         can't reach the unhashed thread in this case. Note that this can
         happen even if g is the group leader, it can exec.
      
      2. Even if while_each_thread() itself was correct, people often use
         it wrongly.
      
         It was never safe to just take rcu_read_lock() and loop unless
         you verify that pid_alive(g) == T, even the first next_thread()
         can point to the already freed/reused memory.
      
      This patch adds signal_struct->thread_head and task->thread_node to
      create the normal rcu-safe list with the stable head.  The new
      for_each_thread(g, t) helper is always safe under rcu_read_lock() as
      long as this task_struct can't go away.
      
      Note: of course it is ugly to have both task_struct->thread_node and the
      old task_struct->thread_group, we will kill it later, after we change
      the users of while_each_thread() to use for_each_thread().
      
      Perhaps we can kill it even before we convert all users, we can
      reimplement next_thread(t) using the new thread_head/thread_node.  But
      we can't do this right now because this will lead to subtle behavioural
      changes.  For example, do/while_each_thread() always sees at least one
      task, while for_each_thread() can do nothing if the whole thread group
      has died.  Or thread_group_empty(), currently its semantics is not clear
      unless thread_group_leader(p) and we need to audit the callers before we
      can change it.
      
      So this patch adds the new interface which has to coexist with the old
      one for some time, hopefully the next changes will be more or less
      straightforward and the old one will go away soon.
      Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
      Reviewed-by: default avatarSergey Dyasly <dserrg@gmail.com>
      Tested-by: default avatarSergey Dyasly <dserrg@gmail.com>
      Reviewed-by: default avatarSameer Nanda <snanda@chromium.org>
      Acked-by: default avatarDavid Rientjes <rientjes@google.com>
      Cc: "Eric W. Biederman" <ebiederm@xmission.com>
      Cc: Frederic Weisbecker <fweisbec@gmail.com>
      Cc: Mandeep Singh Baines <msb@chromium.org>
      Cc: "Ma, Xindong" <xindong.ma@intel.com>
      Cc: Michal Hocko <mhocko@suse.cz>
      Cc: "Tu, Xiaobing" <xiaobing.tu@intel.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      [ kamal: 3.13-stable for backport convenience ]
      Signed-off-by: default avatarKamal Mostafa <kamal@canonical.com>
      e1790aea