Re: memcpy of struct buf, or similar?

[Chris Gilbert <chris%dokein.co.uk@localhost>]

Chris Gilbert wrote:
> Simon Burge wrote:
>> Andrew Doran wrote:
>>
>>> I am trying to fix PR 38761.  [ ... ]
>> FWIW, just sticking a
>>
>>      KASSERT(mutex_owned(&bufcache_lock));
>>
>> before each time b_cflags is modified fails to reach single user when it
>> hits genfs_getpages():
>>
>> panic: kernel diagnostic assertion "mutex_owned(&bufcache_lock)" failed: 
>> file "../../../../miscfs/genfs/genfs_io.c", line 418
> 
> I think thats a false positive, getiobuf gives you a fresh clean buffer,
> which isn't known about to the buffer cache code (yet) Looking at the
> getiobuf it already sets cflags to BC_BUSY, so doing so genfs doesn't
> actually need to do so (and probably shouldn't anyway, otherwise people
> might thing cflags can be played with outside of the bufcache code)
> 
> I've also seen a similar hang.  I had a biolock and a biowait on the
> same  buffer, and bunch of tstiles.
> 
> The biowait was from an open call.  The biolock was from a close call.
> AFAIR the vnode was different, but the buf was the same.
> 
> show buf indicated that the buffer was flagged as done.
> 
> Since applying ad's patch to add a KASSERT for cv_has_waiters(or running
> LOCKDEBUG kernel) I've not been able to repro the issue, build.sh -j8
> (on a quad-core) runs to completion, even with raidframe rebuilding
> underneath it.

Doh, spoke too soon.  With raidframe having completed it's rebuild the
system dived straight into a panic on the next build.sh, with the
biodone KASSERT.  The biodone caller was rf_State_LastState.

Thanks,
Chris