printk: add comment about tricky check for text buffer size
printk: add comment about tricky check for text buffer size

There is no check for potential "text_len" overflow.  It is not needed
because only valid level is detected.  It took me some time to
understand why.  It would deserve a comment ;-)

Signed-off-by: Petr Mladek <9cbcfb1260d253e26a699647bd9cbee55818ea4a@suse.cz>
Cc: Steven Rostedt <43232e92d70cc7aa53504ad0397085ee47bad87f@goodmis.org>
Cc: Frederic Weisbecker <e8a1bf9163cb25e93cfd6540f223b3872ea7ee55@gmail.com>
Cc: Jan Kara <596727c8a0ea4db3ba2ceceedccbacd3d7b371b8@suse.cz>
Cc: Michal Hocko <829500b200af6c2a0eca4dfd5c388e6b8fbe8dc6@suse.cz>
Cc: Kay Sievers <e9264147b413746293e539868c8edff71715e1e3@vrfy.org>
Signed-off-by: Andrew Morton <5c1e68b099950c134891f0b6e179498a8ebe9cf9@linux-foundation.org>
Signed-off-by: Linus Torvalds <69652caca27c8b940640ad396ab71f93cacec34f@linux-foundation.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs