Re: Negative "ios_in_flight" in the 2.4 kernel

From: Jens Axboe
Date: Wed Dec 22 2004 - 06:18:11 EST

On Tue, Dec 21 2004, M. Edward Borasky wrote:
> I've been looking at some "iostat" data from a 2.4.26 machine. The
> device utilizations are 100 percent, even when the disk is idle, which
> is mathematically impossible. By doing some digging, I discovered this
> is a kernel bug, caused by "hd->ios_in_flight" going negative. The
> relevant code appears to my untrained eyes to be in
> drivers/block/ll_rw_blk.c, specifically
> static inline void down_ios(struct hd_struct *hd)
> {
> disk_round_stats(hd);
> --hd->ios_in_flight;
> }
> static inline void up_ios(struct hd_struct *hd)
> {
> disk_round_stats(hd);
> ++hd->ios_in_flight;
> }
> Question: wouldn't a simple refusal to decrement ios_in_flight in
> "down_ios" if it's zero fix this, or am I missing something?

That would paper over the real bug, but it will work for you.

Jens Axboe

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