Re: [libvirt] [PATCH] LXC: make sure fuse thread start to run before we do clone

On Fri, Nov 08, 2013 at 01:30:09PM +0800, Daniel P. Berrange wrote: > On Thu, Nov 07, 2013 at 09:15:43PM +0800, Gao feng wrote: >> I met a problem that container blocked by seteuid/setegid >> which is call in lxcContainerSetID on UP system and libvirt >> compiled with --with-fuse=yes. >> >> I looked into the glibc's codes, and found setxid in glibc >> calls futex() to wait for other threads to change their >> setxid_futex to 0(see setxid_mark_thread in glibc). >> >> since the process created by clone system call will not >> share the memory with the other threads and the context >> of memory doesn't changed until we call execl.(COW) >> >> So if the process which created by clone is called before >> fuse thread being stated, the new setxid_futex of fuse >> thread will not be saw in this process, it will be blocked >> forever. >> >> Maybe this problem should be fixed in glibc, but I send >> this patch as a quick fix. > > Can you show a stack trace of the threads/processes deadlocking I think this is a symptom of setxid not being async-signal-safe like it's required to be. I'm not sure if we have a bug tracker entry for that; if not, it should be added. But if clone() is being used except in a fork-like manner, this is probably invalid application usage too.