Commit a9b107045f

Joran Dirk Greef <joran@ronomon.com>
2020-10-03 14:34:42
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
master
1 parent 95def89
Changed files (1)
lib
std
os
linux
io_uring.zig
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;
         }