On Thu, Dec 31, 2015 at 09:07:59PM +0200, Michael S. Tsirkin wrote:> This defines __smp_xxx barriers for arm, > for use by virtualization. > > smp_xxx barriers are removed as they are > defined correctly by asm-generic/barriers.h > > This reduces the amount of arch-specific boiler-plate code. > > Signed-off-by: Michael S. Tsirkin <mst at redhat.com> > Acked-by: Arnd Bergmann <arnd at arndb.de>In combination with patch 14, this looks like it should result in no change to the resulting code. Acked-by: Russell King <rmk+kernel at arm.linux.org.uk> My only concern is that it gives people an additional handle onto a "new" set of barriers - just because they're prefixed with __* unfortunately doesn't stop anyone from using it (been there with other arch stuff before.) I wonder whether we should consider making the smp memory barriers inline functions, so these __smp_xxx() variants can be undef'd afterwards, thereby preventing drivers getting their hands on these new macros? -- RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net.
On Sat, Jan 02, 2016 at 11:24:38AM +0000, Russell King - ARM Linux wrote:> On Thu, Dec 31, 2015 at 09:07:59PM +0200, Michael S. Tsirkin wrote: > > This defines __smp_xxx barriers for arm, > > for use by virtualization. > > > > smp_xxx barriers are removed as they are > > defined correctly by asm-generic/barriers.h > > > > This reduces the amount of arch-specific boiler-plate code. > > > > Signed-off-by: Michael S. Tsirkin <mst at redhat.com> > > Acked-by: Arnd Bergmann <arnd at arndb.de> > > In combination with patch 14, this looks like it should result in no > change to the resulting code. > > Acked-by: Russell King <rmk+kernel at arm.linux.org.uk> > > My only concern is that it gives people an additional handle onto a > "new" set of barriers - just because they're prefixed with __* > unfortunately doesn't stop anyone from using it (been there with > other arch stuff before.) > > I wonder whether we should consider making the smp memory barriers > inline functions, so these __smp_xxx() variants can be undef'd > afterwards, thereby preventing drivers getting their hands on these > new macros?That'd be tricky to do cleanly since asm-generic depends on ifndef to add generic variants where needed. But it would be possible to add a checkpatch test for this.> -- > RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/ > FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up > according to speedtest.net.
On Sun, Jan 03, 2016 at 11:12:44AM +0200, Michael S. Tsirkin wrote:> On Sat, Jan 02, 2016 at 11:24:38AM +0000, Russell King - ARM Linux wrote:> > My only concern is that it gives people an additional handle onto a > > "new" set of barriers - just because they're prefixed with __* > > unfortunately doesn't stop anyone from using it (been there with > > other arch stuff before.) > > > > I wonder whether we should consider making the smp memory barriers > > inline functions, so these __smp_xxx() variants can be undef'd > > afterwards, thereby preventing drivers getting their hands on these > > new macros? > > That'd be tricky to do cleanly since asm-generic depends on > ifndef to add generic variants where needed. > > But it would be possible to add a checkpatch test for this.Wasn't the whole purpose of these things for 'drivers' (namely virtio/xen hypervisor interaction) to use these? And I suppose most of virtio would actually be modules, so you cannot do what I did with preempt_enable_no_resched() either. But yes, it would be good to limit the use of these things.