Description: Null pointer dereference in trace_writeback_dirty_page() 
References:
 https://bugzilla.redhat.com/show_bug.cgi?id=1306851 (not yet public)
Notes:
 bwh> Problematic call sequence removed by upstream commit appears to be:
 bwh> migrate_page_copy() -> __set_page_dirty_nobuffers()
 bwh> -> account_page_dirtied() -> trace_writeback_dirty_page()
Bugs:
upstream: released (4.4-rc1) [42cb14b110a5698ccf26ce59c4441722605a3743]
3.16-upstream-stable: released (3.16.36) [mm-migrate-dirty-page-without-clear_page_dirty_for_io-etc.patch]
3.2-upstream-stable: N/A ("Vulnerable code not present")
sid: released (4.4.2-1)
3.16-jessie-security: released (3.16.7-ckt25-2+deb8u1) [bugfix/all/mm-migrate-dirty-page-without-clear_page_dirty_for_io-etc.patch]
3.2-wheezy-security: N/A ("Vulnerable code not present")