svn commit: r185526 - in stable/7/sys: . ia64/include
wb at freebie.xs4all.nl
Mon Dec 1 14:03:05 PST 2008
Quoting Marcel Moolenaar, who wrote on Mon, Dec 01, 2008 at 05:40:57PM +0000 ..
> Author: marcel
> Date: Mon Dec 1 17:40:57 2008
> New Revision: 185526
> URL: http://svn.freebsd.org/changeset/base/185526
> MFC rev 179382:
> Work-around a compiler optimization bug, that broke libthr. Massive
> inlining resulted in constant propagation to the extend that cmpval
> was known to the compiler to be URWLOCK_WRITE_OWNER (= 0x80000000U).
> Unfortunately, instead of zero-extending the unsigned constant, it
> was sign-extended. As such, the cmpxchg instruction was comparing
> 0x0000000080000000LU to 0xffffffff80000000LU and obviously didn't
> perform the exchange.
> But, since the value returned by cmpxhg equalled cmpval (when zero-
> extended), the _thr_rtld_lock_release() function thought the exchange
> did happen and as such returned as if having released the lock. This
> was not the case. Subsequent locking requests found rw_state non-zero
> and the thread in question entered the kernel and block indefinitely.
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