sh: Fix EINTR race condition in "wait" and "set -T" using sigsuspend().

When waiting for child processes using "wait" or if "set -T" is in effect, a
signal interrupts the wait. Make sure there is no window where the signal
handler may be invoked (setting a flag) just before going to sleep.

There is a similar race condition in the shell language, but scripts can
avoid it by exiting from the trap handler or enforcing synchronization using
a fifo.

If SIGCHLD is not trapped, a signal handler must be installed for it. Only
install this handler for the duration of the wait to avoid triggering
unexpected [EINTR] errors elsewhere.

Note that for some reason only SIGINT and SIGQUIT interrupt a "wait"
command. This remains the case.

1 files changed, 1 insertions, 0 deletions

diff --git a/bin/sh/trap.h b/bin/sh/trap.h
index bf1250a..61a17ec 100644
--- a/bin/sh/trap.h
+++ b/bin/sh/trap.h
@@ -41,6 +41,7 @@ void clear_traps(void);
 int have_traps(void);
 void setsignal(int);
 void ignoresig(int);
+int issigchldtrapped(void);
 void onsig(int);
 void dotrap(void);
 void setinteractive(int);