On Sat, 1 Apr 2006, Nick Piggin wrote: > All bitop and atomic test_and_set, inc_return, etc etc (ie. everything > that modifies the operand and returns something) needs to be a full > barrier before and after too. Fix ia64 bitops: full barriers in bitops returning a value This fixes up bitops so that they provide a full barrier which are required according to Documentation/atomic_ops.txt. Bit operations use a cmpxchg with a prior load from a volatile pointer. This load is an acquire operation. I think we can simply make the cmpxchg have release semantics in order to produce a full acquire / release cycle. Note that this only fixes up the bit operations if used together with the earlier fix for the clear_bit barriers. We still need a fix for general atomic operations. Signed-off-by: Christoph Lameter <clameter@xxxxxxx> Index: linux-2.6.16-mm2/include/asm-ia64/bitops.h =================================================================== --- linux-2.6.16-mm2.orig/include/asm-ia64/bitops.h 2006-03-31 11:17:53.000000000 -0800 +++ linux-2.6.16-mm2/include/asm-ia64/bitops.h 2006-04-03 11:19:45.000000000 -0700 @@ -163,13 +163,14 @@ test_and_set_bit (int nr, volatile void volatile __u32 *m; CMPXCHG_BUGCHECK_DECL + /* Volatile load = acquire */ m = (volatile __u32 *) addr + (nr >> 5); bit = 1 << (nr & 31); do { CMPXCHG_BUGCHECK(m); old = *m; new = old | bit; - } while (cmpxchg_acq(m, old, new) != old); + } while (cmpxchg_rel(m, old, new) != old); return (old & bit) != 0; } @@ -208,13 +209,14 @@ test_and_clear_bit (int nr, volatile voi volatile __u32 *m; CMPXCHG_BUGCHECK_DECL + /* Volatile load = acquire */ m = (volatile __u32 *) addr + (nr >> 5); mask = ~(1 << (nr & 31)); do { CMPXCHG_BUGCHECK(m); old = *m; new = old & mask; - } while (cmpxchg_acq(m, old, new) != old); + } while (cmpxchg_rel(m, old, new) != old); return (old & ~mask) != 0; } @@ -253,13 +255,14 @@ test_and_change_bit (int nr, volatile vo volatile __u32 *m; CMPXCHG_BUGCHECK_DECL + /* Volatile load = acquire */ m = (volatile __u32 *) addr + (nr >> 5); bit = (1 << (nr & 31)); do { CMPXCHG_BUGCHECK(m); old = *m; new = old ^ bit; - } while (cmpxchg_acq(m, old, new) != old); + } while (cmpxchg_rel(m, old, new) != old); return (old & bit) != 0; } - : send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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