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    • Tetsuo Handa's avatar
      profiling: remove profile=sleep support · b88f5538
      Tetsuo Handa authored
      
      The kernel sleep profile is no longer working due to a recursive locking
      bug introduced by commit 42a20f86 ("sched: Add wrapper for get_wchan()
      to keep task blocked")
      
      Booting with the 'profile=sleep' kernel command line option added or
      executing
      
        # echo -n sleep > /sys/kernel/profiling
      
      after boot causes the system to lock up.
      
      Lockdep reports
      
        kthreadd/3 is trying to acquire lock:
        ffff93ac82e08d58 (&p->pi_lock){....}-{2:2}, at: get_wchan+0x32/0x70
      
        but task is already holding lock:
        ffff93ac82e08d58 (&p->pi_lock){....}-{2:2}, at: try_to_wake_up+0x53/0x370
      
      with the call trace being
      
         lock_acquire+0xc8/0x2f0
         get_wchan+0x32/0x70
         __update_stats_enqueue_sleeper+0x151/0x430
         enqueue_entity+0x4b0/0x520
         enqueue_task_fair+0x92/0x6b0
         ttwu_do_activate+0x73/0x140
         try_to_wake_up+0x213/0x370
         swake_up_locked+0x20/0x50
         complete+0x2f/0x40
         kthread+0xfb/0x180
      
      However, since nobody noticed this regression for more than two years,
      let's remove 'profile=sleep' support based on the assumption that nobody
      needs this functionality.
      
      Fixes: 42a20f86 ("sched: Add wrapper for get_wchan() to keep task blocked")
      Cc: stable@vger.kernel.org # v5.16+
      Signed-off-by: default avatarTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      b88f5538
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