On Fri, Jul 17, 2020 at 09:28:48AM -0500, Seth Forshee wrote:
> On Fri, Jul 17, 2020 at 03:45:10PM +0200, Alberto Milone wrote:
> > On 17/07/2020 15:21, Sebastian Andrzej Siewior wrote:
> > > On 2020-07-17 14:33:31 [+0200], Alberto Milone wrote:
> > >> I checked and CONFIG_DEBUG_LOCK_ALLOC is not enabled in our kernels.
> > > The access to that variable is optimized away if not for debug. I made
> > > this:
> > > | #include <linux/module.h>
> > > | #include <linux/idr.h>
> > > |
> > > | static int le_init(void)
> > > | {
> > > | idr_preload_end();
> > > | return 0;
> > > | }
> > > | module_init(le_init);
> > > |
> > > | static void le_exit(void)
> > > | {
> > > | }
> > > | module_exit(le_exit);
> > > |
> > > | MODULE_DESCRIPTION("driver");
> > > | MODULE_LICENSE("prop");
> > >
> > > and it produced a .ko. Here the "idr_preload_end()" was reduced to
> > > "preempt_enable()" as intended. No access to
> > > "&radix_tree_preloads.lock".
> > >
> > > Sebastian
> > * Subscribing Seth
>
> Looks like the driver is not using idr_preload_end() though, it is
> calling radix_tree_preload_end() which uses radix_tree_preloads whether
> or not CONFIG_DEBUG_LOCK_ALLOC is enabled.
Sorry, I didn't dig deep enough. I see that radix_tree_preload_end() is
expected to opimize away that access too. I wonder if different
toolchains could be ending up with different reults.
Seth
