The mongos crashed with a signal 11 after a lot of "killing old cursor".

I can see a
MessagingPort say send() errno:104 Connection reset by peer CLIENT:52821
Tue Jul 26 10:51:10 [conn177] DBException in process: socket exception
Tue Jul 26 10:51:10 [conn177] MessagingPort say send() errno:32 Broken pipe CLIENT:52821
Tue Jul 26 10:51:10 [conn177] unclean socket shutdown from: CLIENT:52821

just before the crash (see attachment)