Merge commit '5bc66170dc486556a1e36fd384463536573f4b82' into x86/urgent

From Borislav Petkov <bp@amd64.org>:

Below is a RAS fix which reverts the addition of a sysfs attribute
which we agreed is not needed, post-factum. And this should go in now
because that sysfs attribute is going to end up in 3.7 otherwise and
thus exposed to userspace; removing it then would be a lot harder.

This is done as a merge rather than a simple patch/cherry-pick since
the baseline for this patch was not in the previous x86/urgent.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

1 files changed, 18 insertions, 14 deletions

diff --git a/lib/spinlock_debug.c b/lib/spinlock_debug.c
index eb10578ae055..0374a596cffa 100644
--- a/lib/spinlock_debug.c
+++ b/lib/spinlock_debug.c
@@ -107,23 +107,27 @@ static void __spin_lock_debug(raw_spinlock_t *lock)
 {
         u64 i;
         u64 loops = loops_per_jiffy * HZ;
-        int print_once = 1;
 
-        for (;;) {
-                for (i = 0; i < loops; i++) {
-                        if (arch_spin_trylock(&lock->raw_lock))
-                                return;
-                        __delay(1);
-                }
-                /* lockup suspected: */
-                if (print_once) {
-                        print_once = 0;
-                        spin_dump(lock, "lockup suspected");
+        for (i = 0; i < loops; i++) {
+                if (arch_spin_trylock(&lock->raw_lock))
+                        return;
+                __delay(1);
+        }
+        /* lockup suspected: */
+        spin_dump(lock, "lockup suspected");
 #ifdef CONFIG_SMP
-                        trigger_all_cpu_backtrace();
+        trigger_all_cpu_backtrace();
 #endif
-                }
-        }
+
+        /*
+         * The trylock above was causing a livelock.  Give the lower level arch
+         * specific lock code a chance to acquire the lock. We have already
+         * printed a warning/backtrace at this point. The non-debug arch
+         * specific code might actually succeed in acquiring the lock.  If it is
+         * not successful, the end-result is the same - there is no forward
+         * progress.
+         */
+        arch_spin_lock(&lock->raw_lock);
 }
 
 void do_raw_spin_lock(raw_spinlock_t *lock)