[libvirt] [PATCH] Avoid async signal safety problem in glibc's setxid

[Daniel P. Berrange]

On Fri, Nov 15, 2013 at 10:37:53AM -0700, Eric Blake wrote:
> On 11/15/2013 09:20 AM, Daniel P. Berrange wrote:
> > The glibc setxid is supposed to be async signal safe, but
> > libc developers confirm that it is not. This causes a problem
> > when libvirt_lxc starts the FUSE thread and then runs clone()
> > to start the container. If the clone() was done before the
> > FUSE thread has completely started up, then the container
> > will hang in setxid after clone().
> > 
> > The fix is to avoid creating any threads until after the
> > container has been clone()'d. By avoiding any threads in
> > the parent, the child is no longer required to run in an
> > async signal safe context, and we thus avoid the glibc
> > bug.
> > 
> > Signed-off-by: Daniel P. Berrange <berrange at redhat.com>
> > ---
> >  src/lxc/lxc_controller.c | 11 +++++++++--
> >  src/lxc/lxc_fuse.c       | 21 +++++++++++++++------
> >  src/lxc/lxc_fuse.h       |  1 +
> >  3 files changed, 25 insertions(+), 8 deletions(-)
> 
> I can review the code, but I'd feel better if this also got field
> testing as resolving the problem before you push it.
> 
> ACK.

I was able to reproduce the problem one time in 3 without the patch
and it appears gone after applying it.

Daniel
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