Harald van Dijk wrote:
> On 19/12/2020 22:21, Steffen Nurpmeso wrote:
>> Steffen Nurpmeso wrote in
>> <20201219172838.1b-wb%stef...@sdaoden.eu>:
>> |Long story short, after falsely accusing BSD make of not working
>>
>> After dinner i shortened it a bit more, and attach it again, ok?
>> It is terrible, but now less redundant than before.
>> Sorry for being so terse, that problem crosses my head for about
>> a week, and i was totally mislead and if you bang your head
>> against the wall so many hours bugs or misbehaviours in a handful
>> of other programs is not the expected outcome.
>
> I think a minimal test case is simply
>
> all:
> $(SHELL) -c 'trap "echo TTOU" TTOU; set -m; echo all good'
>
> unless I accidentally oversimplified.
>
> The SIGTTOU is caused by setjobctl's xtcsetpgrp(fd, pgrp) call to make
> its newly started process group the foreground process group when job
> control is enabled, where xtcsetpgrp is a wrapper for tcsetpgrp. (That's
> in dash, the other variants may have some small differences.) tcsetpgrp
> has this little bit in its specification:
>
>Attempts to use tcsetpgrp() from a process which is a member of
>a background process group on a fildes associated with its con‐
>trolling terminal shall cause the process group to be sent a
>SIGTTOU signal. If the calling thread is blocking SIGTTOU sig‐
>nals or the process is ignoring SIGTTOU signals, the process
>shall be allowed to perform the operation, and no signal is
>sent.
>
> Ordinarily, when job control is enabled, SIGTTOU is ignored. However,
> when a trap action is specified for SIGTTOU, the signal is not ignored,
> and there is no blocking in place either, so the tcsetpgrp() call is not
> allowed.
>
> The lowest impact change to make here, the one that otherwise preserves
> the existing shell behaviour, is to block signals before calling
> tcsetpgrp and unblocking them afterwards. This ensures SIGTTOU does not
> get raised here, but also ensures that if SIGTTOU is sent to the shell
> for another reason, there is no window where it gets silently ignored.
>
> Another way to fix this is by not trying to make the shell start a new
> process group, or at least not make it the foreground process group.
> Most other shells appear to not try to do this.
This patch implements the blocking of SIGTTOU (and everything else)
while we call tcsetpgrp.
Reported-by: Steffen Nurpmeso
Signed-off-by: Herbert Xu
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
--
Email: Herbert Xu
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
