"Darrick J. Wong" <[EMAIL PROTECTED]> writes: > Hi there, > > I'm seeing a driver hang with 2.6.22-rc3 while being slightly stupid > about offlining CPUs. I suspect that this problem extends beyond a > particular machine, as I've been able to replicate it with an IBM x3650 > and an IBM x3755. This is what I'm doing: > > 1) I tie an IRQ to a particular CPU via /proc/irq/XXX/smp_affinity (IRQ > 4341 is the network card and we're picking on CPU1 in this example): > echo 2 > /proc/irq/4341/smp_affinity > > 2) I then take CPU1 offline: > echo 0 > /sys/devices/system/cpu/cpu1/online > > 3) The kernel prints this: > [ 1101.968040] Breaking affinity for irq 4341 > [ 1102.074019] CPU 1 is now offline > [ 1102.081593] lockdep: not fixing up alternatives. > [ 1112.886919] nfs: server 9.47.66.169 not responding, still trying > > After step 2 the system never sees interrupts from the network card and > remains hung like that until CPU1 is brought back up. It looks as > though the kernel is trying to reroute the IRQ (or so I'm assuming from > the "Breaking affinity" message), but this doesn't ever happen, so the > the kernel stops seeing interrupts from the device. > > Granted, one should not be offlining the CPU that is currently > designated to handle an IRQ, but I suspect that the kernel ought at a > minimum to reject the offlining or route the IRQ to any online CPU > instead of screwing things up.
I agree. > There exists a similar scenario. Set the IRQ affinity to a bunch of > CPUs, watch /proc/interrupts to see which CPU is actually servicing the > interrupts, then offline that CPU. The kernel does not reroute the IRQ > to any of the other CPUs and the device also hangs. > > The furthest that I've dug is that it works on 2.6.17 and is broken in > 2.6.22-rc3 and 2.6.21. Will git-bisect further, but I wanted to know if > anyone else has seen this sort of problem. afaik, this seems to happen > with both IOAPIC and MSI interrupts, possibly more. Thanks for the bug report. I'm chuckling because I just submitted a patch to count that whole code path as broken, based on code review. It is trying to do something that the hardware can not reliably accomplish. Now I am surprised you were seeing this with MSI as well because the hardware should theoretically work in that case. However the irq_fixup code has enough issues that I wouldn't be surprised if it was just doing something stupid and wrong. Eric - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
