Messages in this thread | | | Subject | RE: [PATCH 2.6.21-rc5] Flush MSI-X table writes (rev 3) | Date | Fri, 30 Mar 2007 13:49:20 -0700 | From | "Williams, Mitch A" <> |
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Eric W. Biederman wrote:
>The bug report would be phrased as someone seeing "No irq for vector" >on x86_64. Unless they are a skilled developer they are unlikely to >trace it down to not flushing posted writes to a MSI bar during irq >migration. It part it is a subtle hardware/software race. > >I have seen some unresolved bug reports described this way on machines >that have MSI-X capable hardware. The are against fedora core and I >can't haven't been able to get the reporters to try 2.6.21-rcX and >the other irq back ports don't work so well. > >I currently count 7 drivers in 2.6.21 that are susceptible to the race >this bug closes. > >This version of the patch seems to meet all of the criteria for being >obviously correct, and all it does is insert a stupid readl. Not >very dangerous. > >This fix removes a race between hardware and software that you likely >need to migrate MSI-X irqs a lot to trigger. Which can be the kind of >thing that bytes you after you have a month of uptime. This is a very >nasty condition to track down from bug reports. I'd rather not have a >known culprit out there.
Agreed, this is a subtle bug, and was a real hairball to track down. Even so, I'm surprised that nobody else has dug into this, since it should affect anybody running MSI-X. I originally thought I was seeing a hardware bug, which is why I dug more deeply into the issue.
If Eric is seeing bug reports related to "no vector for IRQ" in the wild, then I have to change my stance and agree that this should be pushed to -stable. Every one of those messages indicates that we hit the race condition.
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