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    SubjectRe: Fix unlock_buffer() to work the same way as bit_unlock()
    On Tue, 28 Mar 2006, Zoltan Menyhart wrote:

    > Why not to use separate bit operations for different purposes?
    >
    > - e.g. "test_and_set_bit_N_acquire()" for lock acquisition
    > - "test_and_set_bit()", "clear_bit()" as they are today
    > - "release_N_clear_bit()"...
    >

    That would force IA64 specifics onto all other architectures.

    Could we simply define these smb_mb__*_clear_bit to be noops
    and then make the atomic bit ops to have full barriers? That would satisfy
    Nick's objections.

    Index: linux-2.6.16/include/asm-ia64/bitops.h
    ===================================================================
    --- linux-2.6.16.orig/include/asm-ia64/bitops.h 2006-03-19 21:53:29.000000000 -0800
    +++ linux-2.6.16/include/asm-ia64/bitops.h 2006-03-28 15:45:08.000000000 -0800
    @@ -45,6 +45,7 @@
    old = *m;
    new = old | bit;
    } while (cmpxchg_acq(m, old, new) != old);
    + smb_mb();
    }

    /**
    @@ -65,7 +66,7 @@
    /*
    * clear_bit() has "acquire" semantics.
    */
    -#define smp_mb__before_clear_bit() smp_mb()
    +#define smp_mb__before_clear_bit() do { } while (0)
    #define smp_mb__after_clear_bit() do { /* skip */; } while (0)

    /**
    @@ -92,6 +93,7 @@
    old = *m;
    new = old & mask;
    } while (cmpxchg_acq(m, old, new) != old);
    + smp_mb();
    }

    /**
    @@ -128,6 +130,7 @@
    old = *m;
    new = old ^ bit;
    } while (cmpxchg_acq(m, old, new) != old);
    + smp_mb();
    }

    /**
    @@ -167,6 +170,7 @@
    old = *m;
    new = old | bit;
    } while (cmpxchg_acq(m, old, new) != old);
    + smp_mb();
    return (old & bit) != 0;
    }

    @@ -212,6 +216,7 @@
    old = *m;
    new = old & mask;
    } while (cmpxchg_acq(m, old, new) != old);
    + smp_mb();
    return (old & ~mask) != 0;
    }

    @@ -257,6 +262,7 @@
    old = *m;
    new = old ^ bit;
    } while (cmpxchg_acq(m, old, new) != old);
    + smp_mb();
    return (old & bit) != 0;
    }

    -
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