Re: [patch] sys_sync livelock fix

[Andrew Morton <akpm@zip.com.au>]

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)
{
	return;
}

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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