irq_work: Fix irq_work_claim() memory ordering

[mirror_ubuntu-jammy-kernel.git] / kernel / irq_work.c

diff --git a/kernel/irq_work.c b/kernel/irq_work.c
index df0dbf4d859b46eea8cdee40bbc05182f6f6b19f..255454a483464e483747952ebf286f57f3c7fbe3 100644 (file)
--- a/kernel/irq_work.c
+++ b/kernel/irq_work.c
@@ -29,24 +29,16 @@ static DEFINE_PER_CPU(struct llist_head, lazy_list);
  */
 static bool irq_work_claim(struct irq_work *work)
 {
-       int flags, oflags, nflags;
+       int oflags;
 
+       oflags = atomic_fetch_or(IRQ_WORK_CLAIMED, &work->flags);
        /*
-        * Start with our best wish as a premise but only trust any
-        * flag value after cmpxchg() result.
+        * If the work is already pending, no need to raise the IPI.
+        * The pairing atomic_xchg() in irq_work_run() makes sure
+        * everything we did before is visible.
         */
-       flags = atomic_read(&work->flags) & ~IRQ_WORK_PENDING;
-       for (;;) {
-               nflags = flags | IRQ_WORK_CLAIMED;
-               oflags = atomic_cmpxchg(&work->flags, flags, nflags);
-               if (oflags == flags)
-                       break;
-               if (oflags & IRQ_WORK_PENDING)
-                       return false;
-               flags = oflags;
-               cpu_relax();
-       }
-
+       if (oflags & IRQ_WORK_PENDING)
+               return false;
        return true;
 }