On Thu, 31 Mar 2016 14:59:51 -0230, Roger H Newell said:

I reverted the previous change, and applied the if(f) test in
file_free. There are no error messages in dmseg and I can mount the
USB device.

That's because Nick's patch is *still* wrong, as the *real* problem
appears to be a memory corruption issue elsewhere.  You don't see it
every mount because it only explodes if a new slab needs to be allocated
after the memory corruption has happened.
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