From: Jonathan Creekmore Date: Thu, 27 Aug 2015 14:04:38 +0000 (-0500) Subject: libxenstore: prefer using the character device X-Git-Tag: archive/raspbian/4.8.0-1+rpi1~1^2~2600 X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=9c89dc95201ffed5fead17b35754bf9440fdbdc0;p=xen.git libxenstore: prefer using the character device With the addition of FMODE_ATOMIC_POS in the Linux 3.14 kernel, concurrent blocking file accesses to a single open file descriptor can cause a deadlock trying to grab the file position lock. If a watch has been set up, causing a read_thread to blocking read on the file descriptor, then future writes that would cause the background read to complete will block waiting on the file position lock before they can execute. This race condition only occurs when libxenstore is accessing the xenstore daemon through the /proc/xen/xenbus file and not through the unix domain socket, which is the case when the xenstore daemon is running as a stub domain or when oxenstored is passed --disable-socket. Accessing the daemon from the true character device also does not exhibit this problem. On Linux, prefer using the character device file over the proc file if the character device exists. Signed-off-by: Jonathan Creekmore Acked-by: Wei Liu Acked-by: Ian Campbell --- diff --git a/tools/xenstore/xs_lib.c b/tools/xenstore/xs_lib.c index af4f75a328..0c7744e80e 100644 --- a/tools/xenstore/xs_lib.c +++ b/tools/xenstore/xs_lib.c @@ -81,6 +81,8 @@ const char *xs_domain_dev(void) #if defined(__RUMPUSER_XEN__) || defined(__RUMPRUN__) return "/dev/xen/xenbus"; #elif defined(__linux__) + if (access("/dev/xen/xenbus", F_OK) == 0) + return "/dev/xen/xenbus"; return "/proc/xen/xenbus"; #elif defined(__NetBSD__) return "/kern/xen/xenbus";