Re: kernel panic while copying files

On 0610T1150, Gary Jennejohn wrote:
> On Tue, 8 Jun 2021 17:54:05 +0200
> Gary Jennejohn <gljennjohn@gmail.com> wrote:
> 
> [big snip]

[..]

> So, I did ``git reset --hard 8dc96b74edb844bb621afeba38fe4af104b13120'',
> which was the penultimate commit made by trasz to clear CCBs on the stack
> after he committed 3394d4239b85b5577845d9e6de4e97b18d3dba58, the change
> to allocate CCBs in UMA.
> 
> Note that I only built the kernel and not world.
> 
> I tried to reset to 3394d4239b85b5577845d9e6de4e97b18d3dba58 itself,
> but without the following commits for CCBs on the stack the kernel
> paniced during startup in AHCI.
> 
> Anyway, this is the minimum set of changes relevant to the uma_ccbs
> story and also results in a panic identical to the one listed above
> when I set kern.cam.da.enable_uma_ccbs=1 and turn on the external USB
> disk.
> 
> So, Warner is probably right and at least the da_uma_ccbs commits
> should be reverted until more research can be done on why the panic
> happens.
> 
> The ada_uma_ccbs commits do not cause any problems in my experience and
> could probably be left in the kernel.

Thank you, I'm working on a fix.  Meanwhile - does the current code
cause any problems with set kern.cam.da.enable_uma_ccbs set to 0?
If it doesn't, it probably doesn't require backing off, since 0 is
the default, and will keep being the default until bugs such as this
one are fixed.