On 06/01/2021 04:45, Herbert Xu wrote:
This patch implements the blocking of SIGTTOU (and everything else)
while we call tcsetpgrp.
Reported-by: Steffen Nurpmeso <steffen@xxxxxxxxxx>
Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
diff --git a/src/jobs.c b/src/jobs.c
index 516786f..809f37c 100644
--- a/src/jobs.c
+++ b/src/jobs.c
@@ -1512,7 +1512,13 @@ showpipe(struct job *jp, struct output *out)
STATIC void
xtcsetpgrp(int fd, pid_t pgrp)
{
- if (tcsetpgrp(fd, pgrp))
+ int err;
+
+ sigblockall(NULL);
+ err = tcsetpgrp(fd, pgrp);
+ sigclearmask();
+
+ if (err)
sh_error("Cannot set tty process group (%s)", strerror(errno));
}
#endif
While this is a step in the right direction, Jilles has already replied
with an explanation of why this is not enough: if the terminal is in
TOSTOP mode, it's not just tcsetpgrp() that needs to be handled, it's
any write as well that may occur while the shell is not in the
foreground process group. While it may be working according to design
for messages written when the shell is not supposed to be in the
foreground process group, it is another story when the shell is both
responsible for taking itself out of the foreground process group and
for writing a message. This is made worse by the fact that there is no
synchronisation with child processes on errors, so even forcibly
restoring the foreground process group may not be enough: unfortunate
scheduling may result in a child process immediately setting the
foreground process group to the child process after the parent process
attempted to restore it to itself. I have not yet seen a good solution
for this.
Cheers,
Harald van Dijk
