On 04/23/2018 04:44 PM, Balbir Singh wrote: > On Mon, Apr 23, 2018 at 8:33 PM, Mahesh Jagannath Salgaonkar > <mah...@linux.vnet.ibm.com> wrote: >> On 04/23/2018 12:21 PM, Balbir Singh wrote: >>> On Mon, Apr 23, 2018 at 2:59 PM, Mahesh J Salgaonkar >>> <mah...@linux.vnet.ibm.com> wrote: >>>> From: Mahesh Salgaonkar <mah...@linux.vnet.ibm.com> >>>> >>>> The current code extracts the physical address for UE errors and then >>>> hooks it up into memory failure infrastructure. On successful extraction >>>> of physical address it wrongly sets "handled = 1" which means this UE error >>>> has been recovered. Since MCE handler gets return value as handled = 1, it >>>> assumes that error has been recovered and goes back to same NIP. This >>>> causes >>>> MCE interrupt again and again in a loop leading to hard lockup. >>>> >>>> Also, initialize phys_addr to ULONG_MAX so that we don't end up queuing >>>> undesired page to hwpoison. >>>> >>>> Without this patch we see: >>>> [ 1476.541984] Severe Machine check interrupt [Recovered] >>>> [ 1476.541985] NIP: [000000001002588c] PID: 7109 Comm: find >>>> [ 1476.541986] Initiator: CPU >>>> [ 1476.541987] Error type: UE [Load/Store] >>>> [ 1476.541988] Effective address: 00007fffd2755940 >>>> [ 1476.541989] Physical address: 000020181a080000 >>>> [...] >>>> [ 1476.542003] Severe Machine check interrupt [Recovered] >>>> [ 1476.542004] NIP: [000000001002588c] PID: 7109 Comm: find >>>> [ 1476.542005] Initiator: CPU >>>> [ 1476.542006] Error type: UE [Load/Store] >>>> [ 1476.542006] Effective address: 00007fffd2755940 >>>> [ 1476.542007] Physical address: 000020181a080000 >>>> [ 1476.542010] Severe Machine check interrupt [Recovered] >>>> [ 1476.542012] NIP: [000000001002588c] PID: 7109 Comm: find >>>> [ 1476.542013] Initiator: CPU >>>> [ 1476.542014] Error type: UE [Load/Store] >>>> [ 1476.542015] Effective address: 00007fffd2755940 >>>> [ 1476.542016] Physical address: 000020181a080000 >>>> [ 1476.542448] Memory failure: 0x20181a08: recovery action for dirty LRU >>>> page: Recovered >>>> [ 1476.542452] Memory failure: 0x20181a08: already hardware poisoned >>>> [ 1476.542453] Memory failure: 0x20181a08: already hardware poisoned >>>> [ 1476.542454] Memory failure: 0x20181a08: already hardware poisoned >>>> [ 1476.542455] Memory failure: 0x20181a08: already hardware poisoned >>>> [ 1476.542456] Memory failure: 0x20181a08: already hardware poisoned >>>> [ 1476.542457] Memory failure: 0x20181a08: already hardware poisoned >>>> [...] >>>> [ 1490.972174] Watchdog CPU:38 Hard LOCKUP >>>> >>>> After this patch we see: >>>> >>>> [ 325.384336] Severe Machine check interrupt [Not recovered] >>> >>> How did you test for this? >> >> By injecting cache SUE using L2 FIR register (0x1001080c). >> >>> If the error was recovered, shouldn't the >>> process have gotten >>> a SIGBUS and we should have prevented further access as a part of the >>> handling >>> (memory_failure()). Do we just need a MF_MUST_KILL in the flags? >> >> We hook it up to memory_failure() through a work queue and by the time >> work queue kicks in, the application continues to restart and hit same >> NIP again and again. Every MCE again hooks the same address to memory >> failure work queue and throws multiple recovered MCE messages for same >> address. Once the memory_failure() hwpoisons the page, application gets >> SIGBUS and then we are fine. >> > > That seems quite broken and not recovered is very confusing. So effectively > we can never recover from a MCE UE.
By not setting handle = 1, the recovery code will fall through machine_check_exception()->opal_machine_check() and then SIGBUS is sent to this process to recover OR head to panic path for kernel UE. We have already hooked up the physical address to memory_failure() which will later hwpoison the page whenever work queue kicks in. This patch makes sure this happens. > I think we need a notion of delayed > recovery then? Where we do recover, but mark is as recovered with delays? Yeah, may be we can set disposition for userspace mce event as recovery in progress/delayed and then print the mce event again from work queue by looking at return value from memory_failure(). What do you think ? > We might want to revisit our recovery process and see if the recovery requires > to turn the MMU on, but that is for later, I suppose. > >> But in case of UE in kernel space, if early machine_check handler >> "machine_check_early()" returns as recovered then >> machine_check_handle_early() queues up the MCE event and continues from >> NIP assuming it is safe causing a MCE loop. So, for UE in kernel we end >> up in hard lockup. >> > > Yeah for the kernel, we need to definitely cause a panic for now, I've got > other > patches for things we need to do for pmem that would allow potential recovery. > > Balbir Singh >
