automount: don't pass non-blocking pipe to kernel.

Creating a pipe with O_NONBLOCK causes both the read and the write end to
be marked as non-blocking.
The "write" end is passed to the kernel autofs module, and it does not
expect a non-blocking pipe.  If it gets -EAGAIN when trying to write
(which is unlikely, but not completely impossible), it will close the
write end of the pipe, which leads to unexpected errors.

So change the code to only set O_NONBLOCK on the "read" end of the
pipe.  This is the only end that systemd interacts with, so the only end
it should be configuring.

diff --git a/src/core/automount.c b/src/core/automount.c
index 6db13ab08fa8becb9b81b1009c4f61c1da925281..6a8373920eac1d66ed01197ae4d52dee4def9107 100644 (file)
--- a/src/core/automount.c
+++ b/src/core/automount.c
@@ -578,10 +578,13 @@ static void automount_enter_waiting(Automount *a) {
                 goto fail;
         }
 
-        if (pipe2(p, O_NONBLOCK|O_CLOEXEC) < 0) {
+        if (pipe2(p, O_CLOEXEC) < 0) {
                 r = -errno;
                 goto fail;
         }
+        r = fd_nonblock(p[0], true);
+        if (r < 0)
+                goto fail;
 
         xsprintf(options, "fd=%i,pgrp="PID_FMT",minproto=5,maxproto=5,direct", p[1], getpgrp());
         xsprintf(name, "systemd-"PID_FMT, getpid_cached());