On Fri, Nov 04, 2022 at 02:53:28AM +0100, Stefano
Brivio wrote:
This happens about every third time on the
two_guests/basic test, and
on that test only: we clone() twice, first to spawn a child, then to
spawn a thread to check that we can enter the target network
namespace.
In this thread, we open a file descriptor associated to the target
namespace. It might happen that it doesn't exist yet: the kernel can
legitimately take its time to create one, after clone(). In this
case, at least on a 5.15 Linux kernel, trying to open that file again
always yields EACCES, and we get stuck there.
This only occurs if we spawn two instances of pasta very close
together, as it's done in the two_guests/basic case.
I couldn't figure out what the race condition is, yet, and especially
if it's a kernel issue or something we're doing wrong. However, if we
wait until the execvp() in the child is done, the issue disappears.
I'm not sure yet if it's just because of timing and this is hiding an
unrelated race condition.
The workaround consists of checking /proc/PID/exe against our own. If
it's different, that means execvp() already completed and we can
proceed. It's rather ugly, but much better than the alternative.
Leave a FIXME there for the moment being.
Signed-off-by: Stefano Brivio <sbrivio(a)redhat.com>
Weird and ugly, but seems like we need it.
Reviewed-by: David Gibson <david(a)gibson.dropbear.id.au>