Date: Mon, 1 Dec 2008 17:40:57 +0000 (UTC) From: Marcel Moolenaar <marcel@FreeBSD.org> To: cvs-src-old@freebsd.org Subject: cvs commit: src/sys/ia64/include atomic.h Message-ID: <200812011741.mB1Hf3Hj089865@repoman.freebsd.org>
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marcel 2008-12-01 17:40:57 UTC
FreeBSD src repository
Modified files: (Branch: RELENG_7)
sys/ia64/include atomic.h
Log:
SVN rev 185526 on 2008-12-01 17:40:57Z by marcel
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.
The work-around is to zero-extend by casting to uint64_t.
Approved by: re (kensmith)
Revision Changes Path
1.11.2.2 +1 -1 src/sys/ia64/include/atomic.h
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