Re: kernel panic while copying files

From: Warner Losh <>
Date: Tue, 08 Jun 2021 15:46:47 UTC
On Tue, Jun 8, 2021 at 8:42 AM Gary Jennejohn <> wrote:

> On Tue, 8 Jun 2021 06:48:19 -0600
> Warner Losh <> wrote:
> > Sorry to reply to myself... had a thought as my brain rested while making
> > tea...
> >
> > I think we may need to consider reverting (or at least not yet enabling)
> > the uma stuff.
> >
> I tested and enabled the UMA CCB stuff immediately after trasz had
> committed it.  I was able to copy files panic-free over USB until
> recently AFAICR.
> I also have had the set since
> then and have never seen a problem there.  Only with USB.

Yes. This specific bug only affects SCSI. And it only affects it when
there's an error that requires a restart. I've not yet had the time to do
an audit for where else the copying is done...

> I'll try booting a new kernel with the uma_ccb sysctl's set to 0
> and see what happens.
> BTW I now have a kernel compiled with -O0 ready to test.