RE: [PATCH diagnostic qspinlock] Diagnostics for excessive lock-drop wait loop time

[Jonas Oberhauser]

Hi Paul,

-----Original Message-----
From: Paul E. McKenney [mailto:paulmck@xxxxxxxxxx] 
> We see systems stuck in the queued_spin_lock_slowpath() loop that waits for the lock to become unlocked in the case where the current CPU has set pending state.

Interesting!
Do you know if the hangs started with a recent patch? What codepaths are active (virtualization/arch/...)? Does it happen extremely rarely? Do you have any additional information?

I saw a similar situation a few years ago in a proprietary kernel, but it only happened once ever and I gave up on looking for the reason after a few days (including some time combing through the compiler generated assembler).

Have fun,
jonas