xfsdump explicitly ignores SIGCHLD in order to prevent librmt rsh
processes from becoming zombies. However, doing so interferes with the
ability for system() to determine a command's exit status.
Setting up a handler for SIGCHLD will not work either, since xfsdump is
now multi-threaded and the main thread (which handles signals) might
handle a child exit before the thread running system() can.
I also attempted to use waitpid() when tearing down a librmt session,
but this has the potential to block indefinitely if there is a problem
on the remote side. (And using WNOHANG tended to never catch the exit.)
In the end, I settled on just not touching SIGCHLD at all. There may be
a zombie rsh when librmt is used, but typically it will be alive until
the end of the backup and in any case will be cleaned up when
xfsdump/restore exits.
Signed-off-by: Bill Kendall <wkendall@xxxxxxx>
---
common/main.c | 11 +++++++----
1 files changed, 7 insertions(+), 4 deletions(-)
diff --git a/common/main.c b/common/main.c
index 5880723..c9a311b 100644
--- a/common/main.c
+++ b/common/main.c
@@ -507,6 +507,13 @@ main( int argc, char *argv[] )
* want to exit when a signal is received. otherwise, hold signals so
* they don't interfere with sys calls; they will be released at
* pre-emption points and upon pausing in the main loop.
+ *
+ * note that since we're multi-threaded, handling SIGCHLD causes
+ * problems with system()'s ability to obtain a child's exit status
+ * (because the main thread may process SIGCHLD before the thread
+ * running system() calls waitpid()). likewise explicitly ignoring
+ * SIGCHLD also prevents system() from getting an exit status.
+ * therefore we don't do anything with SIGCHLD.
*/
sigfillset(&sa.sa_mask);
@@ -514,13 +521,9 @@ main( int argc, char *argv[] )
/* always ignore SIGPIPE, instead handle EPIPE as part
* of normal sys call error handling.
- *
- * explicitly ignore SIGCHLD so that if librmt rsh sessions
- * exit early they do not become zombies.
*/
sa.sa_handler = SIG_IGN;
sigaction( SIGPIPE, &sa, NULL );
- sigaction( SIGCHLD, &sa, NULL );
if ( ! pipeline ) {
sigset_t blocked_set;
--
1.7.0.4
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