Linus Torvalds writes: (Summary) Not the clearest picture, and the "Code:" line in particular is
missing the interesting part, but at a guess it's taking a fault in
put_cred(), which inlines to
put_cred(), which inlines to
put_cred(), which inlines to
if (atomic_dec_and_test(&(cred)->usage))
__put_cred(cred);
and I think it's that "cred" pointer that may be NULL, which makes
"&(cred)->usage" be a NULL pointer too, and you get a page fault when
it tries to decrement the usage count.