alsactl: Fix race at creating a lock file

A race at creating a lock file in state_lock() was discovered
recently: namely, between the first open(O_RDWR) and the second
open(O_RDWR|O_CREAT|O_EXCL) calls, another alsactl invocation may
already create a lock file, then the second open() will return EEXIST,
which isn't handled properly and treated as a fatal error.

In this patch, we check EEXIST case and try again open() with O_RDWR.
This must succeed usually, and if it fails, handle finally as the
fatal error.

BugLink: https://bugzilla.opensuse.org/show_bug.cgi?id=1179904
Signed-off-by: Takashi Iwai <tiwai@suse.de>

alsactl/lock.c

@@ -63,10 +63,15 @@ static int state_lock_(const char *file, int lock, int timeout, int _fd)
 			if (fd < 0) {
 				if (errno == EBUSY || errno == EAGAIN) {
 					sleep(1);
-				} else {
-					err = -errno;
-					goto out;
+					continue;
 				}
+				if (errno == EEXIST) {
+					fd = open(nfile, O_RDWR);
+					if (fd >= 0)
+						break;
+				}
+				err = -errno;
+				goto out;
 			}
 		}
 	}