[PATCH v3] nodedev: ignore EINVAL from libudev in udevEventHandleThread

[christian.ehrhardt at canonical.com]

From: Christian Ehrhardt <christian.ehrhardt at canonical.com>

Certain udev entries might be of a size that makes libudev emit EINVAL
which right now leads to udevEventHandleThread exiting. Due to no more
handling events other elements of libvirt will start pushing for events
to be consumed which never happens causing a busy loop burning a cpu
without any gain.

After evaluation of the example case discussed in in #245 and a test
run ignoring EINVAL it was considered safe to add EINVAL to the ignored
errnos to not exit udevEventHandleThread giving it more resilience.

The root cause is in systemd and by now was discussed and fixed via
https://github.com/systemd/systemd/issues/24987, but hardening libvirt
to be able to better deal with EINVAL returned still is the right thing
to avoid the reported busy loops on systemd with older systemd versions.

Fixes: https://gitlab.com/libvirt/libvirt/-/issues/245

Signed-off-by: Christian Ehrhardt <christian.ehrhardt at canonical.com>
Reviewed-by: Daniel P. Berrangé <berrange at redhat.com>
---
 src/node_device/node_device_udev.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/node_device/node_device_udev.c b/src/node_device/node_device_udev.c
index 24ef1c25a9..2454cab8f8 100644
--- a/src/node_device/node_device_udev.c
+++ b/src/node_device/node_device_udev.c
@@ -1865,10 +1865,12 @@ udevEventHandleThread(void *opaque G_GNUC_UNUSED)
             }
 
             /* POSIX allows both EAGAIN and EWOULDBLOCK to be used
-             * interchangeably when the read would block or timeout was fired
+             * interchangeably when the read would block or timeout was fired.
+             * EINVAL might happen on too large udev entries, ignore those for
+             * the robustness of udevEventHandleThread.
              */
             VIR_WARNINGS_NO_WLOGICALOP_EQUAL_EXPR
-            if (errno != EAGAIN && errno != EWOULDBLOCK) {
+            if (errno != EAGAIN && errno != EWOULDBLOCK && errno != EINVAL) {
             VIR_WARNINGS_RESET
                 virReportSystemError(errno, "%s",
                                      _("failed to receive device from udev "
-- 
2.38.1