1. 21 Apr, 2017 2 commits
    • Kirill A. Shutemov's avatar
      thp: fix MADV_DONTNEED vs clear soft dirty race · ef4c9628
      Kirill A. Shutemov authored
      commit 5b7abeae upstream.
      
      Yet another instance of the same race.
      
      Fix is identical to change_huge_pmd().
      
      See "thp: fix MADV_DONTNEED vs.  numa balancing race" for more details.
      
      Link: http://lkml.kernel.org/r/20170302151034.27829-5-kirill.shutemov@linux.intel.comSigned-off-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      ef4c9628
    • Tejun Heo's avatar
      cgroup, kthread: close race window where new kthreads can be migrated to non-root cgroups · 3144d81a
      Tejun Heo authored
      commit 77f88796 upstream.
      
      Creation of a kthread goes through a couple interlocked stages between
      the kthread itself and its creator.  Once the new kthread starts
      running, it initializes itself and wakes up the creator.  The creator
      then can further configure the kthread and then let it start doing its
      job by waking it up.
      
      In this configuration-by-creator stage, the creator is the only one
      that can wake it up but the kthread is visible to userland.  When
      altering the kthread's attributes from userland is allowed, this is
      fine; however, for cases where CPU affinity is critical,
      kthread_bind() is used to first disable affinity changes from userland
      and then set the affinity.  This also prevents the kthread from being
      migrated into non-root cgroups as that can affect the CPU affinity and
      many other things.
      
      Unfortunately, the cgroup side of protection is racy.  While the
      PF_NO_SETAFFINITY flag prevents further migrations, userland can win
      the race before the creator sets the flag with kthread_bind() and put
      the kthread in a non-root cgroup, which can lead to all sorts of
      problems including incorrect CPU affinity and starvation.
      
      This bug got triggered by userland which periodically tries to migrate
      all processes in the root cpuset cgroup to a non-root one.  Per-cpu
      workqueue workers got caught while being created and ended up with
      incorrected CPU affinity breaking concurrency management and sometimes
      stalling workqueue execution.
      
      This patch adds task->no_cgroup_migration which disallows the task to
      be migrated by userland.  kthreadd starts with the flag set making
      every child kthread start in the root cgroup with migration
      disallowed.  The flag is cleared after the kthread finishes
      initialization by which time PF_NO_SETAFFINITY is set if the kthread
      should stay in the root cgroup.
      
      It'd be better to wait for the initialization instead of failing but I
      couldn't think of a way of implementing that without adding either a
      new PF flag, or sleeping and retrying from waiting side.  Even if
      userland depends on changing cgroup membership of a kthread, it either
      has to be synchronized with kthread_create() or periodically repeat,
      so it's unlikely that this would break anything.
      
      v2: Switch to a simpler implementation using a new task_struct bit
          field suggested by Oleg.
      Signed-off-by: default avatarTejun Heo <tj@kernel.org>
      Suggested-by: default avatarOleg Nesterov <oleg@redhat.com>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Reported-and-debugged-by: default avatarChris Mason <clm@fb.com>
      Signed-off-by: default avatarTejun Heo <tj@kernel.org>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      3144d81a
  2. 18 Apr, 2017 19 commits
  3. 12 Apr, 2017 19 commits