1. 26 Jan, 2019 1 commit
    • Dmitry Safonov's avatar
      tty/ldsem: Wake up readers after timed out down_write() · d93216e5
      Dmitry Safonov authored
      commit 231f8fd0 upstream.
      
      ldsem_down_read() will sleep if there is pending writer in the queue.
      If the writer times out, readers in the queue should be woken up,
      otherwise they may miss a chance to acquire the semaphore until the last
      active reader will do ldsem_up_read().
      
      There was a couple of reports where there was one active reader and
      other readers soft locked up:
        Showing all locks held in the system:
        2 locks held by khungtaskd/17:
         #0:  (rcu_read_lock){......}, at: watchdog+0x124/0x6d1
         #1:  (tasklist_lock){.+.+..}, at: debug_show_all_locks+0x72/0x2d3
        2 locks held by askfirst/123:
         #0:  (&tty->ldisc_sem){.+.+.+}, at: ldsem_down_read+0x46/0x58
         #1:  (&ldata->atomic_read_lock){+.+...}, at: n_tty_read+0x115/0xbe4
      
      Prevent readers wait for active readers to release ldisc semaphore.
      
      Link: lkml.kernel.org/r/20171121132855.ajdv4k6swzhvktl6@wfg-t540p.sh.intel.com
      Link: lkml.kernel.org/r/20180907045041.GF1110@shao2-debian
      Cc: Jiri Slaby <jslaby@suse.com>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: stable@vger.kernel.org
      Reported-by: default avatarkernel test robot <rong.a.chen@intel.com>
      Signed-off-by: default avatarDmitry Safonov <dima@arista.com>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      d93216e5
  2. 16 Jan, 2019 39 commits