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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /lib/dec_and_lock.c
downloadlinux-sh-1da177e4c3f41524e886b7f1b8a0c1fc7321cac2.tar.gz
Linux-2.6.12-rc2v2.6.12-rc2
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
Diffstat (limited to 'lib/dec_and_lock.c')
-rw-r--r--lib/dec_and_lock.c40
1 files changed, 40 insertions, 0 deletions
diff --git a/lib/dec_and_lock.c b/lib/dec_and_lock.c
new file mode 100644
index 000000000000..6658d81e1836
--- /dev/null
+++ b/lib/dec_and_lock.c
@@ -0,0 +1,40 @@
+#include <linux/module.h>
+#include <linux/spinlock.h>
+#include <asm/atomic.h>
+
+/*
+ * This is an architecture-neutral, but slow,
+ * implementation of the notion of "decrement
+ * a reference count, and return locked if it
+ * decremented to zero".
+ *
+ * NOTE NOTE NOTE! This is _not_ equivalent to
+ *
+ * if (atomic_dec_and_test(&atomic)) {
+ * spin_lock(&lock);
+ * return 1;
+ * }
+ * return 0;
+ *
+ * because the spin-lock and the decrement must be
+ * "atomic".
+ *
+ * This slow version gets the spinlock unconditionally,
+ * and releases it if it isn't needed. Architectures
+ * are encouraged to come up with better approaches,
+ * this is trivially done efficiently using a load-locked
+ * store-conditional approach, for example.
+ */
+
+#ifndef ATOMIC_DEC_AND_LOCK
+int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
+{
+ spin_lock(lock);
+ if (atomic_dec_and_test(atomic))
+ return 1;
+ spin_unlock(lock);
+ return 0;
+}
+
+EXPORT_SYMBOL(_atomic_dec_and_lock);
+#endif