[Virtio-fs] [PATCH] virtiofsd: Add gettimeofday to the seccomp whitelist

[Masayoshi Mizuma]

On Wed, Jul 31, 2019 at 04:04:43PM +0100, Stefan Hajnoczi wrote:
> On Tue, Jul 30, 2019 at 05:50:00PM -0400, Masayoshi Mizuma wrote:
> > From: Masayoshi Mizuma <m.mizuma at jp.fujitsu.com>
> > 
> > When I run fsstress on the virtio filesystem, virtiofsd sometimes
> > exits abnormally because it receives SIGSYS.
> > 
> > >From strace:
> >   195852 15:07:47.799331 read(8, "\1\0\0\0\0\0\0\0", 8) = 8 <0.000011>
> >   195852 15:07:47.799379 gettimeofday( <unfinished ...>
> >   195852 15:07:53.354340 <... gettimeofday resumed> <unfinished ...>) = ?
> >   195852 15:07:53.400243 +++ killed by SIGSYS (core dumped) +++
> > 
> > That is because virtiofsd calls gettimeofday() system call but
> > the system call isn't in the seccomp whitelist.
> > 
> > virtiofsd doesn't call gettimeofday() directly. glib library
> > function may call g_get_current_time() and g_get_current_time()
> > calls the system call.
> > 
> > Add gettimeofday() to the seccomp whitelist.
> > 
> > Signed-off-by: Masayoshi Mizuma <m.mizuma at jp.fujitsu.com>
> > ---
> >  contrib/virtiofsd/seccomp.c | 1 +
> >  1 file changed, 1 insertion(+)
> 
> Have you checked that your guest is using the vdso gettimeofday()
> implementation?  gettimeofday() is implemented in userspace without a
> syscall using vdso to improve performance.  If your guest isn't using it
> then performance will be worse.  (There is a fallback code path in the
> vdso that invokes the syscall but I'm not sure it is taken in normal
> cases.)

Yes, my guest is using the vdso gettimeofday().
I'm not sure why virtiofsd calls gettimeofday(), probably the glib
library function calls g_get_current_time() and the glib function
calls gettimeofday().

> 
> The patch is fine though:
> 
> Reviewed-by: Stefan Hajnoczi <stefanha at redhat.com>

Thank you so much!

- Masa