[ViewVC] Diff of: cvs/libev/ev

Comparing libev/ev_linuxaio.c (file contents):
Revision 1.10 by root, Sun Jun 23 02:02:24 2019 UTC vs.
Revision 1.17 by root, Mon Jun 24 02:02:35 2019 UTC

       linuxaio_iocbps [fd]->io.aio_buf = 0;
       anfds [fd].events = 0;
       fd_change (EV_A_ fd, 0);
       /* feed events, we do not expect or handle POLLNVAL */
-      if (ecb_expect_false (res & POLLNVAL))
+      if (expect_false (res & POLLNVAL))
         fd_kill (EV_A_ fd);
       else
         fd_event (
           EV_A_
           fd,
 static int
 linuxaio_get_events_from_ring (EV_P)
 {
   struct aio_ring *ring = (struct aio_ring *)linuxaio_ctx;
-  unsigned head = ring->head;
+  /* the kernel reads and writes both of these variables, */
+  /* as a C extension, we assume that volatile use here */
+  /* both makes reads atomic and once-only */
+  unsigned head = *(volatile unsigned *)&ring->head;
   unsigned tail = *(volatile unsigned *)&ring->tail;
   if (head == tail)
     return 0;
   /* bail out if the ring buffer doesn't match the expected layout */
-  if (ecb_expect_false (ring->magic != AIO_RING_MAGIC)
+  if (expect_false (ring->magic != AIO_RING_MAGIC)
-                        || ring->incompat_features != AIO_RING_INCOMPAT_FEATURES
+                    || ring->incompat_features != AIO_RING_INCOMPAT_FEATURES
-                        || ring->header_length != sizeof (struct aio_ring)) /* TODO: or use it to find io_event[0]? */
+                    || ring->header_length != sizeof (struct aio_ring)) /* TODO: or use it to find io_event[0]? */
     return 0;
+  /* make sure the events up to tail are visible */
   ECB_MEMORY_FENCE_ACQUIRE;
   /* parse all available events, but only once, to avoid starvation */
   if (tail > head) /* normal case around */
     linuxaio_parse_events (EV_A_ ring->io_events + head, tail - head);
     {
       linuxaio_parse_events (EV_A_ ring->io_events + head, ring->nr - head);
       linuxaio_parse_events (EV_A_ ring->io_events, tail);
     }
-  ring->head = tail;
+  /* TODO: we only need a compiler barrier here, not a read fence */
+  ECB_MEMORY_FENCE_RELEASE;
+  /* as an extension to C, we hope that the volatile will make this atomic and once-only */
+  *(volatile unsigned *)&ring->head = tail;
+  /* make sure kernel can see our new head value - probably not required */
+  ECB_MEMORY_FENCE_RELEASE;
   return 1;
 }
 /* read at least one event from kernel, or timeout */
   /* which allows us to pinpoint the errornous iocb */
   for (submitted = 0; submitted < linuxaio_submitcnt; )
     {
       int res = ev_io_submit (linuxaio_ctx, linuxaio_submitcnt - submitted, linuxaio_submits + submitted);
-      if (ecb_expect_false (res < 0))
+      if (expect_false (res < 0))
         if (errno == EAGAIN)
           {
             /* This happens when the ring buffer is full, at least. I assume this means
              * that the event was queued synchronously during io_submit, and thus
              * the buffer overflowed.
             break;
           }
 #if EPOLL_FALLBACK
         else if (errno == EINVAL)
           {
-            /* This hapüpens for unsupported fds, officially, but in my testing,
+            /* This happens for unsupported fds, officially, but in my testing,
              * also randomly happens for supported fds. We fall back to good old
              * poll() here, under the assumption that this is a very rare case.
+             * See https://lore.kernel.org/patchwork/patch/1047453/ for evidence
+             * that the problem is known, but ignored.
              */
             struct iocb *iocb = linuxaio_submits [submitted];
             res = 1; /* skip this iocb */
             linuxaio_rearm_epoll (EV_A_ iocb, EPOLL_CTL_ADD);
   for (;;)
     {
       int idx;
       int res = epoll_wait (backend_fd, events, sizeof (events) / sizeof (events [0]), 0);
-      if (ecb_expect_false (res < 0))
+      if (expect_false (res < 0))
         ev_syserr ("(libev) linuxaio epoll_wait");
       else if (!res)
         break;
       for (idx = res; idx--; )
 int
 linuxaio_init (EV_P_ int flags)
 {
   /* would be great to have a nice test for IOCB_CMD_POLL instead */
   /* also: test some semi-common fd types, such as files and ttys in recommended_backends */
-  if (ev_linux_version () < 0x041200) /* 4.18 introduced IOCB_CMD_POLL */
+#if EPOLL_FALLBACK
+  /* 4.19 made epoll work */
+  if (ev_linux_version () < 0x041300)
     return 0;
+#else
+  /* 4.18 introduced IOCB_CMD_POLL */
+  if (ev_linux_version () < 0x041200)
+    return 0;
+#endif
   linuxaio_ctx = 0;
   if (ev_io_setup (EV_LINUXAIO_DEPTH, &linuxaio_ctx) < 0)
     return 0;
       return 0;
     }
   ev_io_init  (EV_A_ &linuxaio_epoll_w, linuxaio_epoll_cb, backend_fd, EV_READ);
   ev_io_start (EV_A_ &linuxaio_epoll_w);
+  ev_unref (EV_A); /* watcher should not keep loop alive */
 #endif
   backend_modify  = linuxaio_modify;
   backend_poll    = linuxaio_poll;
    ev_syserr ("(libev) linuxaio epoll_create");
   ev_io_stop  (EV_A_ &linuxaio_epoll_w);
   ev_io_init  (EV_A_ &linuxaio_epoll_w, linuxaio_epoll_cb, backend_fd, EV_READ);
   ev_io_start (EV_A_ &linuxaio_epoll_w);
-  ev_unref (EV_A); /* watcher should not keep loop alive */
 #endif
   fd_rearm_all (EV_A);
 }

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Comparing libev/ev_linuxaio.c (file contents): Revision 1.10 by root, Sun Jun 23 02:02:24 2019 UTC vs. Revision 1.17 by root, Mon Jun 24 02:02:35 2019 UTC

Diff Legend

Comparing libev/ev_linuxaio.c (file contents):
Revision 1.10 by root, Sun Jun 23 02:02:24 2019 UTC vs.
Revision 1.17 by root, Mon Jun 24 02:02:35 2019 UTC