[PATCH 14/18] libxl: fork: Make SIGCHLD self-pipe nonblocking

[Ian Jackson <ian.jackson@eu.citrix.com>]

Use the new libxl__pipe_nonblock and _close functions, rather than
open coding the same logic.  Now the pipe is nonblocking, which avoids
a race which could result in libxl deadlocking in a multithreaded
program.

Reported-by: Jim Fehlig <jfehlig@suse.com>
Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>
Cc: Jim Fehlig <jfehlig@suse.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
---
 tools/libxl/libxl.c      |    6 +-----
 tools/libxl/libxl_fork.c |   12 +++---------
 2 files changed, 4 insertions(+), 14 deletions(-)

diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
index 4679b51..3730074 100644
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -171,11 +171,7 @@ int libxl_ctx_free(libxl_ctx *ctx)
      * them; we wish the application good luck with understanding
      * this if and when it reaps them. */
     libxl__sigchld_notneeded(gc);
-
-    if (ctx->sigchld_selfpipe[0] >= 0) {
-        close(ctx->sigchld_selfpipe[0]);
-        close(ctx->sigchld_selfpipe[1]);
-    }
+    libxl__pipe_close(ctx->sigchld_selfpipe);
 
     pthread_mutex_destroy(&ctx->lock);
 
diff --git a/tools/libxl/libxl_fork.c b/tools/libxl/libxl_fork.c
index 2432512..1d0017b 100644
--- a/tools/libxl/libxl_fork.c
+++ b/tools/libxl/libxl_fork.c
@@ -343,17 +343,11 @@ void libxl__sigchld_notneeded(libxl__gc *gc) /* non-reentrant, idempotent */
 
 int libxl__sigchld_needed(libxl__gc *gc) /* non-reentrant, idempotent */
 {
-    int r, rc;
+    int rc;
 
     if (CTX->sigchld_selfpipe[0] < 0) {
-        r = pipe(CTX->sigchld_selfpipe);
-        if (r) {
-            CTX->sigchld_selfpipe[0] = -1;
-            LIBXL__LOG_ERRNO(CTX, LIBXL__LOG_ERROR,
-                             "failed to create sigchld pipe");
-            rc = ERROR_FAIL;
-            goto out;
-        }
+        rc = libxl__pipe_nonblock(CTX, CTX->sigchld_selfpipe);
+        if (rc) goto out;
     }
     if (!libxl__ev_fd_isregistered(&CTX->sigchld_selfpipe_efd)) {
         rc = libxl__ev_fd_register(gc, &CTX->sigchld_selfpipe_efd,
-- 
1.7.10.4