From 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sat, 16 Apr 2005 15:20:36 -0700 Subject: Linux-2.6.12-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! --- arch/x86_64/lib/dec_and_lock.c | 40 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 40 insertions(+) create mode 100644 arch/x86_64/lib/dec_and_lock.c (limited to 'arch/x86_64/lib/dec_and_lock.c') diff --git a/arch/x86_64/lib/dec_and_lock.c b/arch/x86_64/lib/dec_and_lock.c new file mode 100644 index 00000000000..ab43394dc77 --- /dev/null +++ b/arch/x86_64/lib/dec_and_lock.c @@ -0,0 +1,40 @@ +/* + * x86 version of "atomic_dec_and_lock()" using + * the atomic "cmpxchg" instruction. + * + * (For CPU's lacking cmpxchg, we use the slow + * generic version, and this one never even gets + * compiled). + */ + +#include +#include + +int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock) +{ + int counter; + int newcount; + +repeat: + counter = atomic_read(atomic); + newcount = counter-1; + + if (!newcount) + goto slow_path; + + asm volatile("lock; cmpxchgl %1,%2" + :"=a" (newcount) + :"r" (newcount), "m" (atomic->counter), "0" (counter)); + + /* If the above failed, "eax" will have changed */ + if (newcount != counter) + goto repeat; + return 0; + +slow_path: + spin_lock(lock); + if (atomic_dec_and_test(atomic)) + return 1; + spin_unlock(lock); + return 0; +} -- cgit v1.2.3-70-g09d2