irq_work: Fix racy check on work pending flag

[karo-tx-linux.git] / kernel / irq_work.c

diff --git a/kernel/irq_work.c b/kernel/irq_work.c
index 57be1a6cd8daee78d49975a3860e671e6edaee00..64eddd59ed83852262b5655a56e8ebb284dcb119 100644 (file)
--- a/kernel/irq_work.c
+++ b/kernel/irq_work.c
@@ -34,15 +34,21 @@ static DEFINE_PER_CPU(struct llist_head, irq_work_list);
  */
 static bool irq_work_claim(struct irq_work *work)
 {
-       unsigned long flags, nflags;
+       unsigned long flags, oflags, nflags;
 
+       /*
+        * Start with our best wish as a premise but only trust any
+        * flag value after cmpxchg() result.
+        */
+       flags = work->flags & ~IRQ_WORK_PENDING;
        for (;;) {
-               flags = work->flags;
-               if (flags & IRQ_WORK_PENDING)
-                       return false;
                nflags = flags | IRQ_WORK_FLAGS;
-               if (cmpxchg(&work->flags, flags, nflags) == flags)
+               oflags = cmpxchg(&work->flags, flags, nflags);
+               if (oflags == flags)
                        break;
+               if (oflags & IRQ_WORK_PENDING)
+                       return false;
+               flags = oflags;
                cpu_relax();
        }