[PATCH 0/1] Fixup write permission of TLB on powerpc e500 core
a.p.zijlstra at chello.nl
Fri Jul 15 18:20:56 EST 2011
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:
>  353.990181: futex_lock_pi_atomic <-futex_lock_pi
>  353.990185: cmpxchg_futex_value_locked <-futex_lock_pi_atomic
>  353.990191: do_page_fault <-handle_page_fault
>  353.990192: bad_page_fault <-handle_page_fault
>  353.990193: search_exception_tables <-bad_page_fault
>  353.990199: get_user_pages <-fault_in_user_writeable
>  353.990208: mark_page_accessed <-follow_page
>  353.990222: futex_lock_pi_atomic <-futex_lock_pi
>  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?
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