Philippe Gerum wrote: > On Sun, 2006-12-03 at 16:05 +0100, Jan Kiszka wrote: >> Philippe Gerum wrote: >>> On Sun, 2006-12-03 at 15:13 +0100, Jan Kiszka wrote: >>>> Hi, >>>> >>>> I came across a few things in latest 2.6.19-i386-1.6-01 patch: >>>> >>>> The usage of __ipipe_pipelock in __ipipe_common_info_proc is broken (raw >>>> lock used as >>>> Linux lock here), and I do not see any volatile data it could protect >>>> anyway. So let's >>>> remove it. >>> The interrupt status word, and whether any virtual interrupt is >>> allocated or not, are the volatile data protected by this lock on a SMP >>> system. Since this is a common spinlock with no interrupt control >>> required which is only used over the Linux domain (/proc handler), you >>> don't need to go for the _hw() form of it. >> As far as I see, nothing prevents the other users of __ipipe_pipelock to >> be executed over non-root domain (IRQ registration in Xenomai context is >> allowed, no?). >> > > Indeed, this is also the sense of my second reply: > https://mail.gna.org/public/adeos-main/2006-12/msg00004.html > > Which means that our problem is more an issue regarding preemption by > interrupts. > >> But I have to re-check what data for __ipipe_common_info_proc actually >> can be released (I'm not considering inconsistency a problem here). I >> didn't see anything on first review. >> >> Still, this kind of merging of _hw with non-_hw spinlock operations is >> fishy in my eyes. >> > > It's not without interrupt control, provided you accept the possible > side-effects regarding kernel preemption, which /proc handlers do. What > would have been really problematic is a mismatch between > spin_lock_irqsave_hw and spinlock_irqsave forms, and what is really a > bug is the current lack of protection wrt interrupt.
I re-checked the code, and I can only repeat that I see ZERO need for this lock here. All we are reading is the control mask from static IRQ arrays + some bits from the related I-pipe domain. If there is actually something to protect, than it should be calling this proc handler vs. unregistering the domain (and it's proc entry) - but that is only feasible with something like synchronize_sched, i.e. waiting a grace period after unregistering so that all handlers are through. A really uncritical race which exists with a lot of /proc code. Jan
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