On Fri, Aug 02, 2024 at 03:34:48PM +0200, Stefano Brivio wrote:

Ed reported this:

# Error: pasta failed with exit code 1: # Couldn't drop cap 3 from bounding set # : No child processes

in a Podman CI run with tests being run in parallel. The error message itself, by the way, is fixed by commit 1cd773081f12 ("log: Drop newlines in the middle of the perror()-like messages"), but how can we possibly get ECHILD as failure code for prctl()?

Well, we don't, but if we exit early enough, pasta_child_handler() might run before we're even done with isolation steps, and it calls waitid(), which sets errno. We need to restore it before returning from the signal handler (if we return after calling functions that might set it), as signal-safety(7) also implies:

Fetching and setting the value of errno is async-signal-safe provided that the signal handler saves errno on entry and restores its value before returning.

Eventually, we'll probably need to switch to signalfd(2) the day we want to implement multithreading, but this will do for the moment.

Reported-by: Ed Santiago Link: https://github.com/containers/podman/issues/23478 Signed-off-by: Stefano Brivio

Ouch. errno, another of those awful APIs we're stuck with :/ Reviewed-by: David Gibson

--- pasta.c | 3 +++ 1 file changed, 3 insertions(+)

diff --git a/pasta.c b/pasta.c index 572048d..b4a3d99 100644 --- a/pasta.c +++ b/pasta.c @@ -61,6 +61,7 @@ int pasta_child_pid; */ void pasta_child_handler(int signal) { + int errno_save = errno; siginfo_t infop;

(void)signal; @@ -85,6 +86,8 @@ void pasta_child_handler(int signal)

waitid(P_ALL, 0, NULL, WEXITED | WNOHANG); waitid(P_ALL, 0, NULL, WEXITED | WNOHANG); + + errno = errno_save; }

/**

-- David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibson