panic(9) vs. RB_NOSYNC

[Masao Uebayashi]

panic(9) (actually vpanic()) sets RB_NOSYNC when panicstr is already
set.  What is the reasoning of this?

My understanding is that panic() attempts VFS "sync" operation at
first.  If another panic() is triggered during that, give up VFS
"sync".  Is this correct?  If so, how reliable is this design?  I
wonder if attempting such a complex task like VFS "sync" after a panic
is a good idea.