aio: clean up use of volatile

The reason to use volatile (before being copy pasted into other
places) is just to prevent the compiler from doing flag updates
piecemeal. Add a macro wrapper with a comment to make that clearer.

diff --git a/src/backend/storage/ipc/aio.c b/src/backend/storage/ipc/aio.c
index 9b19e92f513ab5ad9b1e99582d1cb8234c23b74c..7528b934b761b9760688431b1019c01c11b0101a 100644 (file)
--- a/src/backend/storage/ipc/aio.c
+++ b/src/backend/storage/ipc/aio.c
@@ -580,10 +580,17 @@ static int my_aio_id;
 /* FIXME: move into PgAioPerBackend / subsume into ->reaped */
 static dlist_head local_recycle_requests;
 
-
 /* io_uring local state */
 struct io_uring local_ring;
 
+
+/*
+ * Ensure that flags is written once, rather than potentially multiple times
+ * (e.g. once and'ing it, and once or'ing it).
+ */
+#define WRITE_ONCE_F(flags) *(volatile PgAioIPFlags*) &(flags)
+
+
 static Size
 AioCtlShmemSize(void)
 {
@@ -1126,7 +1133,7 @@ pgaio_complete_ios(bool in_error)
             * Set flag before calling callback, otherwise we could easily end
             * up looping forever.
             */
-           *(volatile PgAioIPFlags*) &io->flags |= PGAIOIP_SHARED_CALLBACK_CALLED;
+           WRITE_ONCE_F(io->flags) |= PGAIOIP_SHARED_CALLBACK_CALLED;
 
            finished = io_action_cbs[io->type].complete(io);
 
@@ -1138,10 +1145,10 @@ pgaio_complete_ios(bool in_error)
            }
            else
            {
-               Assert((*(volatile PgAioIPFlags*) &io->flags) & (PGAIOIP_SOFT_FAILURE | PGAIOIP_HARD_FAILURE));
+               Assert(io->flags & (PGAIOIP_SOFT_FAILURE | PGAIOIP_HARD_FAILURE));
 
                LWLockAcquire(SharedAIOCtlLock, LW_EXCLUSIVE);
-               *(volatile PgAioIPFlags*) &io->flags =
+               WRITE_ONCE_F(io->flags) =
                    (io->flags & ~(PGAIOIP_REAPED | PGAIOIP_IN_PROGRESS)) |
                    PGAIOIP_DONE |
                    PGAIOIP_SHARED_FAILED;
@@ -1160,7 +1167,7 @@ pgaio_complete_ios(bool in_error)
            dlist_delete_from(&my_aio->reaped, node);
 
            LWLockAcquire(SharedAIOCtlLock, LW_EXCLUSIVE);
-           *(volatile PgAioIPFlags*) &io->flags =
+           WRITE_ONCE_F(io->flags) =
                (io->flags & ~(PGAIOIP_REAPED | PGAIOIP_IN_PROGRESS)) |
                PGAIOIP_DONE |
                PGAIOIP_HARD_FAILURE |
@@ -1221,7 +1228,7 @@ pgaio_complete_ios(bool in_error)
 
                    pg_write_barrier();
 
-                   *(volatile PgAioIPFlags*) &cur->flags =
+                   WRITE_ONCE_F(cur->flags) =
                        (cur->flags & ~(PGAIOIP_REAPED | PGAIOIP_IN_PROGRESS)) |
                        PGAIOIP_DONE |
                        PGAIOIP_FOREIGN_DONE;
@@ -1230,7 +1237,7 @@ pgaio_complete_ios(bool in_error)
                }
                else
                {
-                   *(volatile PgAioIPFlags*) &cur->flags =
+                   WRITE_ONCE_F(cur->flags) =
                        (cur->flags & ~(PGAIOIP_REAPED | PGAIOIP_IN_PROGRESS)) |
                        PGAIOIP_DONE;
 
@@ -1626,7 +1633,7 @@ pgaio_io_prepare_submit(PgAioInProgress *io, uint32 ring)
 
        pg_write_barrier();
 
-       *(volatile PgAioIPFlags*) &cur->flags =
+       WRITE_ONCE_F(cur->flags) =
            (cur->flags & ~PGAIOIP_PENDING) | PGAIOIP_INFLIGHT;
 
        dlist_delete_from(&my_aio->pending, &cur->io_node);
@@ -2030,7 +2037,7 @@ pgaio_io_get(void)
    io->user_referenced = true;
    io->system_referenced = false;
 
-   *(volatile PgAioIPFlags*) &io->flags = PGAIOIP_IDLE;
+   WRITE_ONCE_F(io->flags) = PGAIOIP_IDLE;
 
    io->owner_id = my_aio_id;
 
@@ -2185,9 +2192,7 @@ pgaio_io_retry(PgAioInProgress *io)
 extern void
 pgaio_io_recycle(PgAioInProgress *io)
 {
-   uint32 init_flags = *(volatile PgAioIPFlags*) &io->flags;
-
-   Assert(init_flags & (PGAIOIP_IDLE | PGAIOIP_DONE));
+   Assert(io->flags & (PGAIOIP_IDLE | PGAIOIP_DONE));
    Assert(io->user_referenced);
    Assert(io->owner_id == my_aio_id);
    Assert(!io->system_referenced);
@@ -2986,7 +2991,7 @@ pgaio_uring_wait_one(PgAioContext *context, PgAioInProgress *io, uint64 ref_gene
                errhidestmt(true),
                errhidecontext(true));
 
-       flags = *(volatile PgAioIPFlags*) &io->flags;
+       flags = io->flags;
 
        pg_read_barrier();
 
@@ -3093,7 +3098,7 @@ pgaio_uring_io_from_cqe(PgAioContext *context, struct io_uring_cqe *cqe)
    Assert(io->flags & PGAIOIP_INFLIGHT);
    Assert(io->system_referenced);
 
-   *(volatile PgAioIPFlags*) &io->flags = (io->flags & ~PGAIOIP_INFLIGHT) | PGAIOIP_REAPED;
+   WRITE_ONCE_F(io->flags) = (io->flags & ~PGAIOIP_INFLIGHT) | PGAIOIP_REAPED;
    io->result = cqe->res;
 
    dlist_push_tail(&my_aio->reaped, &io->io_node);