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SubjectRe: [patch] sys_sync livelock fix
Bill Davidsen wrote:
> Alan and/or Linus:
> Am I misreading this or is the Linux implementation of sync() based on
> making the shutdown scripts pause until disk i/o is done? Because I don't
> think commercial unices work that way, I think they work as SuS
> specifies. More reason to rethink this in 2.4 as well as 2.5 and get the
> possible live lock out of the kernel.

IMO, the SuS definition sucks. We really do want to do our best to
ensure that pending writes are committed to disk before sys_sync()
returns. As long as that doesn't involve waiting until mid-August.

For example, ext3 users get to enjoy rebooting with `sync ; reboot -f'
to get around all those silly shutdown scripts. This very much relies
upon the sync waiting upon the I/O.

I mean, according to SUS, our sys_sync() implementation could be

asmlinkage void sys_sync(void)

Because all I/O is already scheduled, thanks to kupdate.

But we want sync to be useful.

> If this were only a performance issue I wouldn't push for prompt
> implementation, but anything which can hang the system, particularly in
> shutdown, is bad.

If shutdown hangs, it's probably due to something else.

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