printk question:why release console_sem after logbuf_lock

[buyitian]

      in the patch 0b5e1c5255e7ee8670e077e8224e5c2281229a5b, it releases console_sem after logbuf_lock,  the description of this patch is as below: Release console_sem after unlocking the logbuf_lock so that we don't
generate wakeups while holding logbuf_lock. This avoids some lock
inversion troubles once we remove the lockdep_off bits between
logbuf_lock and rq->lock (prints while holding rq->lock vs doing
wakeups while holding logbuf_lock).There's of course still an actual deadlock where the printk()s under
rq->lock will issue a wakeup from the up() call, but lockdep won't
warn about that since semaphores are not tracked.         could you please give me a detail example about the issue it tries to fix? thanks. 		 	   		  
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