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uloop: Fix race condition in SIGCHLD handling

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When uloop_process_add() is called outside of uloop_run(), i.e. not
from a callback (which is the case of at least utrace and ujail),
child events can be missed. The reason is that when SIGCHILD handler
is installed in uloop_run(), after the uloop_process_add() is called,
then an initial signal could be missed.

Commit 4e3a47a ("uloop: use a waker for notifying sigchld and loop
cancel events", 2016-06-09) solved a similar problem and introduced
uloop_init() but forgot to move a call to uloop_setup_signals() there.
This is what this commit does.

Now, uloop_process_add() can be called any time after uloop_init()
without missing any event.

Signed-off-by: Michal Sojka <sojkam1@fel.cvut.cz>
Acked-by: Yousong Zhou <yszhou4tech@gmail.com>
This commit is contained in:
Michal Sojka 2017-09-12 13:12:31 +02:00 committed by Yousong Zhou
parent fd57eea9f3
commit 7a1057604e
1 changed files with 8 additions and 8 deletions
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16
uloop.c
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@ -116,6 +116,8 @@ static int waker_init(void)
return 0;
}
static void uloop_setup_signals(bool add);
int uloop_init(void)
{
if (uloop_init_pollfd() < 0)
@ -126,6 +128,8 @@ int uloop_init(void)
return -1;
}
uloop_setup_signals(true);
return 0;
}
@ -525,12 +529,7 @@ int uloop_run_timeout(int timeout)
int next_time = 0;
struct timeval tv;
/*
* Handlers are only updated for the first call to uloop_run() (and restored
* when this call is done).
*/
if (!uloop_run_depth++)
uloop_setup_signals(true);
uloop_run_depth++;
uloop_status = 0;
uloop_cancelled = false;
@ -553,14 +552,15 @@ int uloop_run_timeout(int timeout)
uloop_run_events(next_time);
}
if (!--uloop_run_depth)
uloop_setup_signals(false);
--uloop_run_depth;
return uloop_status;
}
void uloop_done(void)
{
uloop_setup_signals(false);
if (poll_fd >= 0) {
close(poll_fd);
poll_fd = -1;