bcachefs-tools: fix endian problems between bit spinlocks and futexes

[bcachefs-tools-debian] / include / linux / bit_spinlock.h

diff --git a/include/linux/bit_spinlock.h b/include/linux/bit_spinlock.h
index 62b91afaf9e0bb275f6cf5666ac53f77937a7a7d..873f08c2e24c8de10d15c800f97ebfb3dbca5263 100644 (file)
--- a/include/linux/bit_spinlock.h
+++ b/include/linux/bit_spinlock.h
@@ -6,38 +6,78 @@
 #include <linux/futex.h>
 #include <urcu/futex.h>
 
+/*
+ * The futex wait op wants an explicit 32-bit address and value. If the bitmap
+ * used for the spinlock is 64-bit, cast down and pass the right 32-bit region
+ * for the in-kernel checks. The value is the copy that has already been read
+ * from the atomic op.
+ *
+ * The futex wake op interprets the value as the number of waiters to wake (up
+ * to INT_MAX), so pass that along directly.
+ */
+static inline void do_futex(int nr, unsigned long *addr, unsigned long v, int futex_flags)
+{
+       u32 *addr32 = (u32 *) addr;
+       u32 *v32 = (u32 *) &v;
+       int shift = 0;
+
+       futex_flags |= FUTEX_PRIVATE_FLAG;
+
+#if BITS_PER_LONG == 64
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+       shift = (nr >= 32) ? 1 : 0;
+#else
+       shift = (nr < 32) ? 1 : 0;
+#endif
+#endif
+       if (shift) {
+               addr32 += shift;
+               v32 += shift;
+       }
+       /*
+        * The shift to determine the futex address may have cast away a
+        * literal wake count value. The value is capped to INT_MAX and thus
+        * always in the low bytes of v regardless of bit nr. Copy in the wake
+        * count to whatever 32-bit range was selected.
+        */
+       if (futex_flags == FUTEX_WAKE_PRIVATE)
+               *v32 = (u32) v;
+       futex(addr32, futex_flags, *v32, NULL, NULL, 0);
+}
+
 static inline void bit_spin_lock(int nr, unsigned long *_addr)
 {
-       u32 mask, *addr = ((u32 *) _addr) + (nr / 32), v;
+       unsigned long mask;
+       unsigned long *addr = _addr + (nr / BITS_PER_LONG);
+       unsigned long v;
 
-       nr &= 31;
-       mask = 1U << nr;
+       nr &= BITS_PER_LONG - 1;
+       mask = 1UL << nr;
 
        while (1) {
                v = __atomic_fetch_or(addr, mask, __ATOMIC_ACQUIRE);
                if (!(v & mask))
                        break;
 
-               futex(addr, FUTEX_WAIT|FUTEX_PRIVATE_FLAG, v, NULL, NULL, 0);
+               do_futex(nr, addr, v, FUTEX_WAIT);
        }
 }
 
 static inline void bit_spin_wake(int nr, unsigned long *_addr)
 {
-       u32 *addr = ((u32 *) _addr) + (nr / 32);
-
-       futex(addr, FUTEX_WAKE|FUTEX_PRIVATE_FLAG, INT_MAX, NULL, NULL, 0);
+       do_futex(nr, _addr, INT_MAX, FUTEX_WAKE);
 }
 
 static inline void bit_spin_unlock(int nr, unsigned long *_addr)
 {
-       u32 mask, *addr = ((u32 *) _addr) + (nr / 32);
+       unsigned long mask;
+       unsigned long *addr = _addr + (nr / BITS_PER_LONG);
 
-       nr &= 31;
-       mask = 1U << nr;
+       nr &= BITS_PER_LONG - 1;
+       mask = 1UL << nr;
 
        __atomic_and_fetch(addr, ~mask, __ATOMIC_RELEASE);
-       futex(addr, FUTEX_WAKE|FUTEX_PRIVATE_FLAG, INT_MAX, NULL, NULL, 0);
+       do_futex(nr, addr, INT_MAX, FUTEX_WAKE);
 }
 
 #endif /* __LINUX_BIT_SPINLOCK_H */