Messages in this thread | | | From | Bartlomiej Zolnierkiewicz <> | Subject | Re: Possible IRQ lock inversion from 2.6.29-Linus-03321-gbe0ea69 (2.6.29-git) | Date | Sat, 28 Mar 2009 14:36:09 +0100 |
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On Friday 27 March 2009, Jonathan Corbet wrote: > On Fri, 27 Mar 2009 13:54:35 +0100 > Bartlomiej Zolnierkiewicz <bzolnier@gmail.com> wrote: > > > I remember looking a bit more closely into the issue and not seeing > > the problem with the locking (though I could have missed something): > > > > file->f_lock is never taken in hard-irq or soft-irq context and in > > the only place where file->f_lock is taken with fasync_lock hold we're > > protected against IRQs by write_lock_irq(). > > I do think that the warning is spurious at this time. > > > [ Despite not being a problem now I think that changing spin_[un]lock() > > to *_irq() variants for file->f_lock could be (given that it really > > fixes the warning) more viable long-term solution than adding special > > lockdep handling (well, it could be that one day file->f_lock is used > > in soft-irq context and then the irq lock inversion issue will become > > a real one) and shouldn't incurr performance penalty since we hold it > > only for a very brief time. ] > > We could do that. When I made the change I'd verified that there were > no users in IRQ context, and I couldn't really see why there should > be. I'd rather avoid adding all those IRQ disables if I can avoid it. > > How about, instead, just reversing the order of lock acquisition in > fasync_helper()? That would increase the hold time for f_lock, but I > have a hard time seeing that being a real problem. I'm running with > the following now; all seems well. I'll send it up in a bit if nobody > gripes.
This is even better and works just fine here.
Thanks, Bart
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