zig

commit a9b107045fb0592f813ffd9f5fef3e2cbfd2ac89 (tree)
parent 95def89c232acc53c926731fe5143ea093128d73
Author: Joran Dirk Greef <joran@ronomon.com>
Date:   Sat,  3 Oct 2020 14:34:42 +0200

Use load acquire semantics when reading the SQPOLL wakeup flag

Ensures that the wakeup flag is read after the tail pointer has been
written. It's important to use memory load acquire semantics for the
flags read, otherwise the application and the kernel might not agree on
the consistency of the wakeup flag, leading to I/O starvation.

Refs: https://github.com/axboe/liburing/commit/6768ddcc562adb6ea141cf508bccecb6be8ce666
Refs: https://github.com/axboe/liburing/issues/219

Diffstat:
M
lib/std/os/linux/io_uring.zig
 | 
2
+-

1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/lib/std/os/linux/io_uring.zig b/lib/std/os/linux/io_uring.zig
@@ -247,7 +247,7 @@ pub const IO_Uring = struct {
     pub fn sq_ring_needs_enter(self: *IO_Uring, submitted: u32, flags: *u32) bool {
         assert(flags.* == 0);
         if ((self.flags & linux.IORING_SETUP_SQPOLL) == 0 and submitted > 0) return true;
-        if ((@atomicLoad(u32, self.sq.flags, .Unordered) & linux.IORING_SQ_NEED_WAKEUP) != 0) {
+        if ((@atomicLoad(u32, self.sq.flags, .Acquire) & linux.IORING_SQ_NEED_WAKEUP) != 0) {
             flags.* |= linux.IORING_ENTER_SQ_WAKEUP;
             return true;
         }