On Fri, 2011-07-15 at 16:07 +0800, Shan Hai wrote:The following test case could reveal a bug in the futex_lock_pi()
BUG: On FUTEX_LOCK_PI, there is a infinite loop in the futex_lock_pi()
on Powerpc e500 core.
Cause: The linux kernel on the e500 core has no write permission on
the COW page, refer the head comment of the following test code.
ftrace on test case:
[000] 353.990181: futex_lock_pi_atomic<-futex_lock_pi
[000] 353.990185: cmpxchg_futex_value_locked<-futex_lock_pi_atomic
[snip]
[000] 353.990191: do_page_fault<-handle_page_fault
[000] 353.990192: bad_page_fault<-handle_page_fault
[000] 353.990193: search_exception_tables<-bad_page_fault
[snip]
[000] 353.990199: get_user_pages<-fault_in_user_writeable
[snip]
[000] 353.990208: mark_page_accessed<-follow_page
[000] 353.990222: futex_lock_pi_atomic<-futex_lock_pi
[snip]
[000] 353.990230: cmpxchg_futex_value_locked<-futex_lock_pi_atomic
[ a loop occures here ]
But but but but, that get_user_pages(.write=1, .force=0) should result
in a COW break, getting our own writable page.
What is this e500 thing smoking that this doesn't work?