Hello, On Thu, Oct 03, 2024 at 08:38:48AM -0600, Jens Axboe wrote: ... > >>> 3144 spin_lock(&iocg->ioc->lock); > >>> > >>> But why is this not spin_lock_irq()? I haven't analyzed this so maybe it's > >>> fine. > >> > >> That's a bug. > >> > > > > I could obviously write this patch but I feel stupid writing the > > commit message. My level of understanding is Monkey See Monkey do. > > Could you take care of this? > > Sure - or let's add Tejun who knows this code better. Ah he's already > added. Tejun? Yeah, that should be spin_lock_irq() for consistency but at the same time it doesn't look like anything is actually grabbing that lock (or blkcg->lock nesting outside of it) from an IRQ context, so no actual deadlock scenario exists and lockdep doesn't trigger. > > So somewhere we're taking a lock in the IRQ handler and this can lead > > to a deadlock? I thought this would have been caught by lockdep? > > It's nested inside blkcg->lock which is IRQ safe, that is enough. But > doing a quick scan of the file, the usage is definitely (widly) > inconsistent. Most times ioc->lock is grabbed disabling interrupts, but Hmm... the only place I see is the one Dan pointed out. > there are also uses that doesn't disable interrupts, coming from things > like seq_file show paths which certainly look like they need it. lockdep > should certainly warn about this, only explanation I have is that nobody > bothered to do that :-) The locks are intended to be IRQ-safe but it looks like they don't need to be at least for now. I'll send a patch to update the ioc_weight_write() pair. Thanks. -- tejun
