On Thu, Dec 03, 2015 at 12:08:11PM +0000, Peter Rosin wrote: > Russell King wrote: > > On Thu, Dec 03, 2015 at 11:38:20AM +0000, Peter Rosin wrote: > > > Russell King wrote: > > > > On Thu, Dec 03, 2015 at 08:33:13AM +0000, Peter Rosin wrote: > > > > > I wrote: > > > > > > If I enable CONFIG_CPU_SW_DOMAIN_PAN, I sometimes (but not always) > > > > > > get the > > > > > > following (or very similar) on boot. > > > > > > > > > > I should have said "if I don't disable", as the option is "default y". > > > > > > > > > > Also, if it survives on boot, below is an example of later trouble > > > > > (after > > > > > 30+ minutes on this occasion). > > > > > > > > Please apply this patch so we (might) get a slightly better oops dump, > > > > and then try to reproduce. > > > > > > Sure thing, but it's still "DAC: 00000051"... > > > > Thanks, that confirms that something in the uaccess-with-memcpy code > > is clearing the DACR back to 0x51. > > > > This has come up several times before, and I really can't spot the > > problem in this code, so I've always said to disable the > > uaccess-with-memcpy code. Personally, I'd like to see the back > > of that code... > > Ok, but it's not me doing crazy things if that's what you are implying > (not saying that you are), because the sama5_defconfig has > > CONFIG_UACCESS_WITH_MEMCPY=y > > So, something needs to happen or sama5 remains default-broken.
I have no solution for this, other than saying that uaccess-with-memcpy seems to be (for some unknown reason) incompatible with SW PAN. Out of the two features, I'd go for SW PAN over uaccess-with-memcpy, but others will have a different opinion. The real solution is to track down what's going on and why, but I don't think anyone has the motivation to do that. I've looked into this problem, and I've been unable to identify what's going on here. I can see no reason for the DACR to be set to 0x51 in this code. The entry path into this code is via __copy_to_user(), which saves and sets the DACR to 0x55 before calling arm_copy_to_user(), which for uaccess-with-memcpy() is in arch/arm/lib/uaccess_with_memcpy.c. That tail-calls into __copy_to_user_memcpy(), which should run with the DACR set to 0x55. The only place that the DACR is changed is inside __put_user(), which saves the DACR before also setting it to 0x55, and then restores the old DACR value, which, because the old value was 0x55, will have no effect. So, I can see no way that the DACR should ever be 0x51 inside __copy_to_user_memcpy(), but you are seeing such a scenario. I've no idea how you could ever get a value of 0x51 out of the DACR within this code. -- FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
