Re: [resend-without-rfc] powernv/kdump: Fix cases where the kdump kernel can get HMI's
From: Nicholas Piggin <npiggin@gmail.com>
Date: 2017-12-08 04:53:14
On Fri, 8 Dec 2017 14:35:33 +1100 Balbir Singh [off-list ref] wrote:
Certain HMI's such as malfunction error propagate through all threads/core on the system. If a thread was offline prior to us crashing the system and jumping to the kdump kernel, bad things happen when it wakes up due to an HMI in the kdump kernel. There are several possible ways to solve this problem 1. Put the offline cores in a state such that they are not woken up for machine check and HMI errors. This does not work, since we might need to wake up offline threads occasionally to handle TB errors 2. Ignore HMI errors, setup HMEER to mask HMI errors, but this still leads the window open for any MCEs and masking them for the duration of the dump might be a concern 3. Wake up offline CPUs, as in send them to crash_ipi_callback (not wake them up as in mark them online as seen by the scheduler). kexec does a wake_online_cpus() call, this patch does something similar, but instead sends an IPI and forces them to crash_ipi_callback Care is taken to enable this only for powenv platforms via crash_wake_offline (a global value set at setup time). The crash code sends out IPI's to all CPU's which then move to crash_ipi_callback and kexec_smp_wait(). We don't grab the pt_regs for offline CPU's. Signed-off-by: Balbir Singh <bsingharora@gmail.com> --- Nick reviewed the patches and asked if 1. We need to do anything on the otherside of the kernel? The answer is not clear at this point, but I don't want to block this patch as it fixes a critical problem with kdump in SMT=2/1 mode 2. We should do this for other platforms The answer is same as above, other platforms require testing and I can selectively enable them as needed as I test them
Yeah I didn't intend those as a nack for the patch... It's a bit annoying to have these selections between online cpus and present cpus depending on kdump. We don't want to do a full CPU online in the kdump path of course, but what if the crash code has a call that can IPI offline CPUs to get them into the crash callback, rather than put it in the general NMI IPI code?
quoted hunk ↗ jump to hunk
@@ -187,6 +188,14 @@ static void pnv_smp_cpu_kill_self(void) WARN_ON(lazy_irq_pending()); /* + * For kdump kernels, we process the ipi and jump to + * crash_ipi_callback. For more details see the description + * at crash_wake_offline + */ + if (kdump_in_progress()) + crash_ipi_callback(NULL); + + /* * If the SRR1 value indicates that we woke up due to * an external interrupt, then clear the interrupt. * We clear the interrupt before checking for the
I think you need to do this _after_ clearing the interrupt, otherwise you get a lost wakeup window, don't you? Thanks, Nick