Re: 2.4.1-ac5 - The loopback hang saga continues

From: Billy Harvey (
Date: Wed Feb 07 2001 - 20:02:08 EST

> It appears that the loopback-hang parasite is alive and well in 2.4.1-ac5.
> I've done several tests and I thus provide the following information:
> The bug is independent of UP or SMP configured.. it hung both ways, but the
> box itself is UP.
> It appears to hang when internal buffers get filled. The way I see it, copying
> files from disk to the loopback device (which is a file on the same disk)
> begins to read from the disk. When the internal read buffer is full, the
> kernel's queued writes start activating and the data gets copied to the
> loopback file. This process repeats over and over, as it should normally.
> Sometimes however, during a read from the disk, it fills up its buffers and
> then never makes the accompanying write. In fact, the entire device freezes on
> the read.
> I was able to lessen the frequency of hanging by using the -v flag and tapping
> ^S and ^Q to temporarily 'pause' copying. This ensures that the read buffer
> will never become full to the point where it could cause the hang, and appears
> to work -- until it came across the libc.a file. There was no way to pause it
> here because nothing is being outputted to the screen while it's copying
> libc.a. Unfortunately, it fills the buffer too quick and hangs 100% every time.
> The disk is totally nonresponsive at this point, and a hard reset is necessary.
> I hope this helps anyone who is still tracking down the loopback problem.
> Regards,
> Byron
> --
> Byron Stanoszek Ph: (330) 644-3059

I can confirm this. The system totally locks when this occurs. I let
it sit all night when it did this the last time, and it didn't

It requires a large file transfer to usually invoke it.

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