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

[Gao feng]

On 11/09/2013 03:42 AM, Rich Felker wrote:
> 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.
> 

I post a patch to the glibc community, but I can't find my patch on the
mail list archive. the patch is attached. do you think this glibc patch
is needed or we just should add some bug tracker on manpage?


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