Things Which Sleep

You can never call the following routines while holding a spinlock, as they may sleep. This also means you need to be in user context.

• Accesses to userspace:

  • copy_from_user()

  • copy_to_user()

  • get_user()

  • put_user()

• kmalloc(GFP_KERNEL)

• down_interruptible() and down()

  There is a down_trylock() which can be used inside interrupt context, as it will not sleep. up() will also never sleep.

printk() can be called in any context, interestingly enough.