sched: add wait_var_event_io()

It is not currently possible to wait wait_var_event for an io_schedule()
style wait.  This patch adds wait_var_event_io() for that purpose.

Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20240925053405.3960701-7-neilb@suse.de

diff --git a/include/linux/wait_bit.h b/include/linux/wait_bit.h
index 6aea10efca3d7b602e82174bb2769aee5029042e..6346e26fbfd17a39dd3934cb3a63516ac9db53e1 100644 (file)
--- a/include/linux/wait_bit.h
+++ b/include/linux/wait_bit.h
@@ -281,6 +281,9 @@ __out:      __ret;                                                          \
 #define __wait_var_event(var, condition)                               \
        ___wait_var_event(var, condition, TASK_UNINTERRUPTIBLE, 0, 0,   \
                          schedule())
+#define __wait_var_event_io(var, condition)                            \
+       ___wait_var_event(var, condition, TASK_UNINTERRUPTIBLE, 0, 0,   \
+                         io_schedule())
 
 /**
  * wait_var_event - wait for a variable to be updated and notified
@@ -306,6 +309,34 @@ do {                                                                       \
        __wait_var_event(var, condition);                               \
 } while (0)
 
+/**
+ * wait_var_event_io - wait for a variable to be updated and notified
+ * @var: the address of variable being waited on
+ * @condition: the condition to wait for
+ *
+ * Wait for an IO related @condition to be true, only re-checking when a
+ * wake up is received for the given @var (an arbitrary kernel address
+ * which need not be directly related to the given condition, but
+ * usually is).
+ *
+ * The process will wait on a waitqueue selected by hash from a shared
+ * pool.  It will only be woken on a wake_up for the given address.
+ *
+ * This is similar to wait_var_event(), but calls io_schedule() instead
+ * of schedule().
+ *
+ * The condition should normally use smp_load_acquire() or a similarly
+ * ordered access to ensure that any changes to memory made before the
+ * condition became true will be visible after the wait completes.
+ */
+#define wait_var_event_io(var, condition)                              \
+do {                                                                   \
+       might_sleep();                                                  \
+       if (condition)                                                  \
+               break;                                                  \
+       __wait_var_event_io(var, condition);                            \
+} while (0)
+
 #define __wait_var_event_killable(var, condition)                      \
        ___wait_var_event(var, condition, TASK_KILLABLE, 0, 0,          \
                          schedule())