On Mon, May 13, 2024, at 06:03, Paul E. McKenney wrote: > On Mon, May 13, 2024 at 12:50:07PM +0900, Akira Yokosawa wrote: >> On Sun, 12 May 2024 07:44:25 -0700, Paul E. McKenney wrote: >> > On Sun, May 12, 2024 at 08:02:59AM +0200, John Paul Adrian Glaubitz wrote: >> > So why didn't the people running current mainline on pre-EV56 Alpha >> > systems notice? One possibility is that they are upgrading their >> > kernels only occasionally. Another possibility is that they are seeing >> > the failures, but are not tracing the obtuse failure modes back to the >> > change(s) in question. Yet another possibility is that the resulting >> > failures are very low probability, with mean times to failure that are >> > so long that you won't notice anything on a single system. >> >> Another possibility is that the Jensen system was booted into uni processer >> mode. Looking at the early boot log [1] provided by Ulrich (+CCed) back in >> Sept. 2021, I see the following by running "grep -i cpu": >> >> >> > [1] https://marc.info/?l=linux-alpha&m=163265555616841&w=2 >> >> [ 0.000000] Memory: 90256K/131072K available (8897K kernel code, 9499K rwdata, \ >> 2704K rodata, 312K init, 437K bss, 40816K reserved, 0K cma-reserved) [ 0.000000] \ >> random: get_random_u64 called from __kmem_cache_create+0x54/0x600 with crng_init=0 [ \ >> 0.000000] SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=1, Nodes=1 [ 0.000000] >> ^^^^^^ >> >> Without any concurrent atomic updates, the "broken" atomic accesses won't >> matter, I guess. > > True enough! On the other hand, you would get the same broken behavior on any SMP machine running a kernel that has support for EV5 or earlier enabled in a multiplatform kernel. It doesn't really matter if it's running on hardware that supports BWX or not as long as the compiler doesn't generate those instructions. If I understand it correctly, simply running rcutorture on a large alpha machine with a 'defconfig' kernel from the past two years should trigger some bugs even if you don't run into them that frequently on light usage, right? Arnd
