Re: [RFC][PATCHv4 6/6] printk: remove zap_locks() function

[Peter Zijlstra]

On Fri, Nov 25, 2016 at 04:01:13PM +0100, Petr Mladek wrote:
> On Fri 2016-10-28 00:49:33, Sergey Senozhatsky wrote:
> > 2) Since commit cf9b1106c81c ("printk/nmi: flush NMI messages on the
> >    system panic") panic attempts to zap the `logbuf_lock' spin_lock to
> >    successfully flush nmi messages to `logbuf'.
> 
> Note that the same code is newly used to flush also the printk_safe
> per-CPU buffers. It means that logbuf_lock is zapped also when
> flushing these new buffers.
> 

Note that (raw_)spin_lock_init() as done here and in
printk_nmi_flush_on_panic() can wreck the lock state and doesn't ensure
a subsequent spin_lock() of said lock will actually work.

The very best solution is to simply ignore the lock in panic situations
rather than trying to wreck it.