Coding: Fix Sleep While Atomic (Slideshow)

Simple Spinlock Usage: spin_lock()

  • Replace struct mutex with spinlock_t

  • Use plain spin_lock()

  • Test

    • Two tight loops injecting events via ioctl()

    • Generate interrupts in parallel

    • ⟶ hang sooner or later

Discuss Call Chain, IRQ State

  • Event: spin lock taken from ISR directly, top-level

  • What if caller already holds a spinlock?

  • ⟶ spin_unlock() unconditionally reenables interrupts

  • ⟶ conversely, spin_lock() unconditionally disables interrupts

Enter spin_lock_irqsave(), spin_unlock_irqrestore()

  • Fix

  • Test

  • Gone

Ah, kmalloc()

  • event.c: still using GFP_KERNEL

    • Called from interrupt service routine!

  • CONFIG_DEBUG_ATOMIC_SLEEP would have complained loudly

    ../../../../../_images/menuconfig-lock-debugging1.png

Fix

  • Pass gfp_t parameter to my_event_list_add()