[libvirt] [PATCH] Avoid async signal safety problem in glibc's setxid
Daniel P. Berrange
berrange at redhat.com
Sat Nov 16 10:11:42 UTC 2013
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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