Re: [git pull] scheduler fixes

Matthew Wilcox
2008-05-11T11:14:52Z

On Sun, May 11, 2008 at 05:03:06AM -0600, Matthew Wilcox wrote:
> This might be the problem that causes the missing wakeups. If you have a
> semaphore with n=2, and four processes calling down(), tasks A and B
> acquire the semaphore and tasks C and D go to sleep. Task A calls up()
> and wakes up C. Then task B calls up() and doesn't wake up anyone
> because C hasn't run yet. I think we need another wakeup when task C

Er, I mis-wrote there.

Task A calls up() and wakes up C. Then task B calls up() and wakes up C
again because C hasn't removed itself from the list yet. D never
receives a wakeup. The solution is for C to pass a wakeup along to the
next in line. (The solution remains the same).

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