Andreas Oberritter wrote: > Oliver Endriss wrote: > > ... > > @Andreas: > > Could you please explain in more detail what bad things might happen? > > To quote myself from the changelog: This fixes a deadlock discovered > by lockdep. I re-read the commit message, but it still does not ring any bells. Could you please post the lockdep output? > The lock is used in process context (e.g. DMX_START) and might also be > used from interrupt context (e.g. dvb_dmx_swfilter). Correct: - dvb_dmx_swfilter uses spin_lock (called from irq, tasklet, whatever) - DMX_START uses spin_lock_irq (called from process) -> ok (see below). > >From http://osdir.com/ml/kernel.janitors/2002-08/msg00022.html: > > "spin_lock_irq disables local interrupts and then takes the spin_lock. > If you know you're in process context and other users may be in > interrupt context, this is the correct call to make. > > spin_lock_irqsave saves local interrupt state into the flags variable, > disables interrupts, then takes the spin_lock. spin_unlock_irqrestore > restores the local state saved in the flags. Use this variant if you > don't know whether you're in interrupt or process context." > > So, if the assumtions above are correct, then spin_lock_irq must be > used by all functions called from process context and > spin_lock_irqsave must be used by all functions called from an unknown > context. Correct. [1] If you want to lock a process against an interrupt handler, - the process must use spin_lock_irq() - the interrupt can use spin_lock() A routine has to use spin_lock_irqsave if (and only if) process and irq call the routine concurrently. I do not see yet how this might happen. (Basically, the same happens when locking between tasklet and process context, except that it is sufficient to use spin_lock_bh instead of spin_lock_irq.) Regards Oliver -- ---------------------------------------------------------------- VDR Remote Plugin 0.4.0: http://www.escape-edv.de/endriss/vdr/ ---------------------------------------------------------------- -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
